Medical Terminology

This glossary is provided by the Hypersomnia Foundation to help our community understand the information contained on our website. If you have suggestions for additions and/or changes to this glossary, please email us at .

 

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  • actigraphy
    Actigraphy is used to non-invasively measure body movement. An actigraph, which looks like an oversized watch, is typically worn on the nondominant wrist (that is, if you are right-handed, you would wear it on your left wrist). It contains an accelerometer and records movements, which are then downloaded from the device and analyzed offline. When combined with a sleep diary or sleep log, actigraphy can be used to measure sleep patterns and circadian rhythms.
  • adjunct
    In medicine, an adjunct is a supplement to another main therapeutic treatment.
  • agonist
    An agonist is a chemical that binds to and activates a receptor. The result is a biologic response — an action. (An antagonist is the opposite of an agonist.)
  • allele
    An allele is a variant form of a gene. Each gene resides at a specific locus (location on a chromosome) in two copies; one copy of the gene is inherited from each parent. The copies, however, are not necessarily identical. When the copies of a gene differ from each other, they are known as alleles. A given gene may have multiple different alleles, but only two alleles are present at the gene’s locus in any individual. (Read more HERE.)
  • allosteric modulator
    Allosteric modulators are substances that indirectly influence or modulate the effects of an agonist at a receptor. For example, with respect to the GABAA receptor, positive allosteric modulators increase the activity of the GABAA receptor protein in the central nervous system of mammals. (Examples of positive allosteric modulators include alcohol, benzodiazepines [such as Valium], benzodiazepine-receptor agonists [such as Ambien or Lunesta], anesthetic gases, and propofol.) In contrast, negative allosteric modulators inhibit or decrease the activity of the GABAA receptor protein. (Examples of negative allosteric modulators or inhibitors of GABAA activity are flumazenil, bicuculline, pentylenetetrazol, and gabazine.)
  • amphetamines
    Dextroamphetamine (Dexedrine, Zenzedi, ProCentra), amphetamine (Adzenys XR, Adzenys ER, Dyanavel XR, Evekeo), and combination dextroamphetamine-amphetamine (Adderall, Biphetamine, Mydayis) are central nervous system stimulants approved by the U.S. FDA for ADHD and narcolepsy. Other amphetamine derivatives include lisdexamfetamine (Vyvanse). They are more stimulating than methylphenidate (Ritalin), but all of them have potential side effects including dependence, aggressive behavior, dental problems and heart problems. Read more on HF’s Treatment web page HERE and at MedlinePlus.gov as follows: 1) amphetamine, 2) dextroamphetamine, 3) combination dextroamphetamine-amphetamine, and 4) lisdexamphetamine.
  • ANS
    The autonomic nervous system (ANS) controls several basic bodily functions, including heart rate, body temperature, breathing rate, digestion, skin sensation, bladder, sweat glands, and metabolism. The ANS regulates functions that are involuntary or that we usually cannot consciously influence. The ANS is made up of 3 parts: (1) sympathetic nervous system (responsible for the body's "fight or flight" response, by increasing the heart rate and releasing energy); (2) parasympathetic nervous system (responsible for controlling body processes during relaxation and other ordinary situations, including slowing down heart rate and reducing blood pressure); and (3) enteric nervous system (responsible for governing the function of the gastrointestinal system through a mesh-like system of neurons [also called nerve cells]).
  • antagonist
    An antagonist is a chemical that binds to and inactivates a receptor. The result is a blocking of a biologic response. (An antagonist is the opposite of an agonist.)
  • apathy
    Apathy refers to a lack of feeling, emotion, interest, or concern for self or others.
  • armodafinil
    Armodafinil (Nuvigil, Acronite, Armoda, Armod, Artivil, Neoresotyl, R-Modawake, Waklert, Modavital) is a non-stimulant wake-promoting medication. While it is not completely known how this medication works, it appears to influence the brain chemistry that increases wakefulness, particularly the neurotransmitter dopamine. Armodafinil is a single-isomer of modafinil (Provigil), another wake-promoting medication, and was approved by the U.S. FDA in 2007 to improve wakefulness in people with excessive sleepiness caused by narcolepsy, obstructive sleep apnea and shift work sleep disorder. Armodafinil can interact with hormonal birth control to make it less effective (learn more HERE), and can result in a life-threatening rash. In addition, armodafinil can sometimes result in headaches, which, if severe enough, can cause a user to reduce the dosage, thereby limiting the effectiveness of the medication. Read more about armodafinil at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • ARS
    Autonomic reflex screen (ARS) testing includes a variety of tests to measure how heart rate and blood pressure change in response to changes in position (e.g., tilt table testing) and breathing. The testing may also evaluate how the nerves that regulate sweat glands respond to stimulation.
  • atomoxetine
    Atomoxetine (Strattera, Attera, Attentin, Axepta, Axetra, Stramox, Tomoxetin) is a non-stimulant medication approved by the U.S. FDA in 2002 to treat attention-deficit hyperactivity disorder (ADHD). It belongs to the group of medicines called selective norepinephrine reuptake inhibitors (NRIs), and is believed to work by increasing norepinephrine and dopamine. It increases wakefulness, but generally less strongly than the medications which act directly on dopamine. A medication similar to atomoxetine is reboxetine, which is approved in Europe but is not currently approved in the U.S. However, reboxetine was granted Orphan Drug Designation (ODD) status by the FDA in October 2018 for the treatment of narcolepsy. Read more about atomoxetine at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • automatic behavior
    An automatic behavior is one that is performed without conscious self-control or memory. “Automatic behavior consists of purposeful but inappropriate activities that occur with the patient partially asleep. Patients relay stories of putting milk containers in the microwave oven, cereal bowls in the dryer, or even missing an exit on the highway.” Read more HERE.
  • autonomic nervous system
    The autonomic nervous system (ANS) controls several basic bodily functions, including heart rate, body temperature, breathing rate, digestion, skin sensation, bladder, sweat glands, and metabolism. The ANS regulates functions that are involuntary or that we usually cannot consciously influence. The ANS is made up of 3 parts: (1) sympathetic nervous system (responsible for the body's "fight or flight" response, by increasing the heart rate and releasing energy); (2) parasympathetic nervous system (responsible for controlling body processes during relaxation and other ordinary situations, including slowing down heart rate and reducing blood pressure); and (3) enteric nervous system (responsible for governing the function of the gastrointestinal system through a mesh-like system of neurons [also called nerve cells]).
  • autonomic reflex screen test
    Autonomic reflex screen (ARS) testing includes a variety of tests to measure how heart rate and blood pressure change in response to changes in position (e.g., tilt table testing) and breathing. The testing may also evaluate how the nerves that regulate sweat glands respond to stimulation.
  • b

  • baclofen
    Baclofen (Lioresal, Gablofen, Beklo, Baclodol, Flexibac, Kemstro, Liofen, Lyflex, Clofen, Muslofen, Baklofen, Sclerofen) is a gamma-aminobutyric acid (GABA) agonist used primarily as a muscle relaxant to relieve the painful and uncomfortable muscle spasms caused by a variety of conditions. It is known to be particularly useful in treating muscle spasticity (i.e., continuous contraction or tightness) associated with spinal cord injury, cerebral palsy, and multiple sclerosis. It was approved by the U.S. FDA in 1977 for the management of reversible spasticity. Some small studies suggest possible therapeutic potential for baclofen as a treatment for sleep disorders; however, a 2009 study by researchers in Taiwan, involving 26 teenagers with narcolepsy, found that while baclofen increased total sleep time and delta waves during sleep, it did not improve daytime sleepiness or cataplexy. Read more about baclofen at MedlinePlus.gov HERE.
  • BDI
    The Beck Depression Inventory (BDI) is a widely used 21-item questionnaire for measuring severity of depression.
  • Beck Depression Inventory
    The Beck Depression Inventory (BDI) is a widely used 21-item questionnaire for measuring severity of depression.
  • BeyondSleepy
    Our slogan “Let’s get #BeyondSleepy” is a metaphor intended to provoke a discussion or consideration of the many ways that idiopathic hypersomnia and related disorders affect people. We strive to “get beyond” all the life-altering symptoms, including “beyond sleepiness,” “get beyond” the stigma, “get beyond” the lack of understanding, “get beyond” misdiagnosis and length of time to a diagnosis, and “get beyond” off-label treatments.
  • biomarker
    A biomarker (which is a short for biological marker) is a substance that is found in blood, other body fluids, or tissues that indicates a normal or abnormal process, a condition or disease, or the effects of treatment.
  • bupropion
    Bupropion (Wellbutrin, Zyban, Forfivo, Aplenzin) is an antidepressant that is known to have wake-promoting effects. It is a norepinephrine-dopamine reuptake inhibitor (NDRI), unlike most other antidepressants which are selective serotonin reuptake inhibitor (SSRIs). It works by inhibiting the reabsorption of two important brain chemicals – norepinephrine and dopamine. Read more about bupropion at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • c

  • carnitine
    Carnitine is a substance that our bodies make in our liver and kidneys. It is then stored in our skeletal muscles, heart, brain, and sperm. Carnitine helps to turn fat into energy (via fatty-acid oxidation). Our bodies usually make enough carnitine to satisfy all of our needs, but some people don't have enough carnitine because their bodies either can’t make enough or can’t transport the carnitine into tissues so it can be used. In a 2013 study involving 30 people with NT1, researchers found that oral carnitine supplementation improved narcolepsy symptoms (including daytime sleepiness), possibly by increasing fatty-acid oxidation. Read more about carnitine on HF’s Treatment web page HERE.
  • cataplexy
    Cataplexy is a sudden and temporary episode of muscle weakness that is typically triggered by strong emotions (for example, laughing, crying, terror), during which the person remains fully conscious and aware.
  • CBT
    Cognitive behavioral therapy (CBT) is a form of therapy that is goal-oriented; it involves examining and changing your behavior and patterns of thoughts, with the guidance and coaching of a therapist specially trained in CBT. A number of clinical studies have shown CBT to be effective for many conditions, including depression and anxiety. Read more about Getting Support from a Mental Health Professional.
  • CCR1/CCR3
    The CCR1 and CCR3 (C-C chemokine receptor 1 and 3) genes are involved in regulating the body’s response to bacteria, viruses, and other substances that the body perceives to be harmful or not a part of itself (that is, “foreign”).
  • CDH
    The central disorders of hypersomnolence (CDH), as defined by the ICSD-3, include narcolepsy type 1, narcolepsy type 2, idiopathic hypersomnia, and Kleine-Levin syndrome. They also include insufficient sleep syndrome and hypersomnia caused by a medical condition, medication or substance, or psychiatric condition.
  • central disorders of hypersomnolence
    The central disorders of hypersomnolence (CDH), as defined by the ICSD-3, include narcolepsy type 1, narcolepsy type 2, idiopathic hypersomnia, and Kleine-Levin syndrome. They also include insufficient sleep syndrome and hypersomnia caused by a medical condition, medication or substance, or psychiatric condition.
  • cerebrospinal fluid
    Cerebrospinal fluid (CSF) is a clear, colorless liquid that bathes the brain and spinal cord. Its primary purpose is to protect the brain and spinal cord, acting as a barrier and shock absorber. This fluid also circulates nutrients and chemicals that are filtered from the blood and removes waste products, antibodies, chemicals, and disease-causing substances away from the brain and spinal-cord tissue into the bloodstream.
  • CGI
    There are two types of CGI (Clinical Global Impression) scales, which vary depending on the precise issue the professional or researcher is assessing. The first is the Clinical Global Impression-Severity (CGI-S) scale, which is a 7-point scale that healthcare professionals or researchers (clinicians) use to rate the patient’s severity of illness at the time of assessment, relative to the clinician’s past experience with patients who have the same diagnosis. Responses include: 1) normal or not at all ill; 2) borderline mentally ill; 3) mildly ill; 4) moderately ill; 5) markedly ill; 6) severely ill; or 7) among the most extremely ill patients. The second scale is the Clinical Global Impression-Improvement scale (CGI-I), which is a 7-point scale that requires the clinician to assess how much the patient's illness has improved or worsened relative to a baseline state at the beginning of an intervention. Responses include: 1) very much improved; 2) much improved; 3) minimally improved; 4) no change; 5) minimally worse; 6) much worse; or 7) very much worse.
  • chemokine receptor 1 and 3
    The CCR1 and CCR3 (C-C chemokine receptor 1 and 3) genes are involved in regulating the body’s response to bacteria, viruses, and other substances that the body perceives to be harmful or not a part of itself (that is, “foreign”).
  • clarithromycin
    Clarithromycin (Biaxin) is in a class of medications called macrolide antibiotics, and is derived from erythromycin. It works as an antibiotic by stopping the growth of bacteria, and was approved by the U.S. FDA in 1991 for treating certain infections. It has been shown in a small, randomized trial to improve daytime sleepiness and quality of life more than a placebo, in those people with primary hypersomnias related to excess activity of the GABA system. Read more about clarithromycin at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • Clinical Global Impression scales
    There are two types of CGI (Clinical Global Impression) scales, which vary depending on the precise issue the professional or researcher is assessing. The first is the Clinical Global Impression-Severity (CGI-S) scale, which is a 7-point scale that healthcare professionals or researchers (clinicians) use to rate the patient’s severity of illness at the time of assessment, relative to the clinician’s past experience with patients who have the same diagnosis. Responses include: 1) normal or not at all ill; 2) borderline mentally ill; 3) mildly ill; 4) moderately ill; 5) markedly ill; 6) severely ill; or 7) among the most extremely ill patients. The second scale is the Clinical Global Impression-Improvement scale (CGI-I), which is a 7-point scale that requires the clinician to assess how much the patient's illness has improved or worsened relative to a baseline state at the beginning of an intervention. Responses include: 1) very much improved; 2) much improved; 3) minimally improved; 4) no change; 5) minimally worse; 6) much worse; or 7) very much worse.
  • clinical trial
    A clinical trial is one of two main types of clinical studies, which are research studies involving human participants. A clinical trial tests (or tries out) an intervention – a potential drug, medical device, activity, or procedure. It also is referred to as an interventional clinical study. The other main type of clinical study is an observational study. In an observational study, researchers observe participants on their current treatment plan and track health outcomes. Read more HERE.
  • cognitive behavioral therapy
    Cognitive behavioral therapy (CBT) is a form of therapy that is goal-oriented; it involves examining and changing your behavior and patterns of thoughts, with the guidance and coaching of a therapist specially trained in CBT. A number of clinical studies have shown CBT to be effective for many conditions, including depression and anxiety. Read more about Getting Support from a Mental Health Professional.
  • comorbid
    The term comorbid refers to two or more different medical conditions, which may or may not be related, occurring at the same time.
  • complex sleep apnea
    Complex sleep apnea is a relatively rare sleep disorder in which central apneas either persist or emerge once obstructive sleep apnea is treated (usually with CPAP or BiPAP). The underlying cause of complex sleep apnea is not well understood but is thought to involve the peripheral chemoreceptors and brain stem responses. Read more about complex sleep apnea HERE.
  • control subject
    In an experiment or clinical trial, control subjects make up a group of participants who have characteristics similar to those of the treatment group, but they do not receive the treatment being studied. In an observational study, the control subjects have similar characteristics as those participants being studied, except that they do not have the symptom, disease, syndrome, or disorder being studied.
  • crossover study
    In a crossover study, each participant receives both the placebo and the active drug for a defined period of time. The order in which people receive the different treatments is determined randomly, and the responses that participants have to each of the different treatments are compared. Crossover studies can be double-blind, single-blind, or unblinded.
  • CSF
    Cerebrospinal fluid (CSF) is a clear, colorless liquid that bathes the brain and spinal cord. Its primary purpose is to protect the brain and spinal cord, acting as a barrier and shock absorber. This fluid also circulates nutrients and chemicals that are filtered from the blood and removes waste products, antibodies, chemicals, and disease-causing substances away from the brain and spinal-cord tissue into the bloodstream.
  • d

  • derealization
    Derealization is the repeated sense of feeling as if you are observing yourself from outside your body or that things around you aren't real, or both. Derealization has been recognized by researchers as one of the possible symptoms of certain sleep disorders, including idiopathic hypersomnia (IH) and Kleine-Levin syndrome (KLS).
  • Diagnostic and Statistical Manual of Mental Disorders
    The Diagnostic and Statistical Manual of Mental Disorders (DSM) is an authoritative volume produced by the APA (American Psychiatric Association) that defines and classifies mental disorders (including many neurological disorders) in order to improve diagnoses, treatment, and research. The 5th edition (DSM-5) is the 2013 update and a product of more than 10 years of effort by hundreds of international experts in all aspects of mental health.
  • differential diagnosis
    In medicine, the process of considering other diagnoses which have similar symptoms or signs.
  • dopamine
    Dopamine is a neurotransmitter that helps regulate movement, attention, and emotional responses, including reward-motivated behavior.
  • double-blind
    A double-blind trial or study is one in which neither the people who are doing the experiment nor the people who are the subjects of the experiment know which of the groups being studied is receiving the substance under investigation (active group) or is receiving the placebo (control group).
  • DSM
    The Diagnostic and Statistical Manual of Mental Disorders (DSM) is an authoritative volume produced by the APA (American Psychiatric Association) that defines and classifies mental disorders (including many neurological disorders) in order to improve diagnoses, treatment, and research. The 5th edition (DSM-5) is the 2013 update and a product of more than 10 years of effort by hundreds of international experts in all aspects of mental health.
  • dysautonomia
    Dysautonomia, or autonomic dysfunction, is a broad term that refers to any of a number of conditions that result from a problem or disturbance in the autonomic nervous system.
  • e

  • EDS
    Excessive daytime sleepiness (EDS) refers to persistent sleepiness that occurs despite adequate or even prolonged nighttime sleep.
  • EEG
    Electroencephalography (EEG) is the measurement and recording of the brain's electrical activity by a typically non-invasive monitoring method.
  • effector cell
    An effector cell is a muscle, gland or organ cell that is capable of responding to a stimulus.
  • electroencephalography
    Electroencephalography (EEG) is the measurement and recording of the brain's electrical activity by a typically non-invasive monitoring method.
  • EMA
    The European Medicines Agency (EMA), which was established in 1995, is a decentralized agency of the European Union, located in London. The Agency is responsible for the scientific evaluation of medicines developed by pharmaceutical companies for use in the European Union. (It is similar to the Food & Drug Administration [FDA] in the United States.)
  • encoding
    With respect to genetics, encoding means that our genes provide the blueprint or code for arranging amino acids so that they make proteins in our bodies.
  • endogenous

    An endogenous substance originates from or is produced within an organism (such as the human body), tissue or cell. (The opposite of endogenous is exogenous.)

  • Epworth Sleepiness Scale
    The Epworth Sleepiness Scale (ESS) is a set of questions that measures how likely you are to fall asleep in each of 8 situations. For example, you might respond to a question about dozing with an answer of 0 (would never doze), 1 (slight chance of dozing), 2 (moderate chance of dozing), or 3 (high chance of dozing). Your responses to all of the eight questions are combined for a final score, which can range between 0 and 24. Higher scores indicate higher levels of daytime sleepiness. Most doctors and scientists consider scores of 10 or higher to indicate abnormal sleepiness.
  • ESS
    The Epworth Sleepiness Scale (ESS) is a set of questions that measures how likely you are to fall asleep in each of 8 situations. For example, you might respond to a question about dozing with an answer of 0 (would never doze), 1 (slight chance of dozing), 2 (moderate chance of dozing), or 3 (high chance of dozing). Your responses to all of the eight questions are combined for a final score, which can range between 0 and 24. Higher scores indicate higher levels of daytime sleepiness. Most doctors and scientists consider scores of 10 or higher to indicate abnormal sleepiness.
  • etiology
    Etiology refers to the cause or basis of a disease or condition.
  • European Medicines Agency
    The European Medicines Agency (EMA), which was established in 1995, is a decentralized agency of the European Union, located in London. The Agency is responsible for the scientific evaluation of medicines developed by pharmaceutical companies for use in the European Union. (It is similar to the Food & Drug Administration [FDA] in the United States.)
  • excessive daytime sleepiness
    Excessive daytime sleepiness (EDS) refers to persistent sleepiness that occurs despite adequate or even prolonged nighttime sleep.
  • exogenous

    An exogenous substance originates from or is produced outside an organism (such as the human body), tissue or cell. (The opposite of exogenous is endogenous.)

  • f

  • FDA
    The United States Food and Drug Administration (FDA) is an agency within the U.S. Department of Health and Human Services. It is responsible for protecting the public health by ensuring the safety, effectiveness, quality, and security of human and veterinary drugs, vaccines, and other biologic products and medical devices. The FDA is also responsible for the safety and security of most of our nation’s food supply and of cosmetics.
  • flumazenil
    Flumazenil is a GABA receptor antagonist that is FDA-approved in the U.S. as an intravenous (IV) medication to reverse excessive or prolonged sedation suspected to be caused by benzodiazepines (e.g., Valium, Ambien, etc.). It is not FDA-approved for the treatment of IH or any other central disorder of hypersomnolence. However, as with any medication approved by the FDA, physicians can choose to prescribe flumazenil “off-label” for indications other than that for which it is approved. This includes the use of flumazenil for the treatment of IH and related sleep disorders. Because flumazenil is currently approved in liquid form for IV use, it must be formulated into a transdermal cream or lozenge (for topical or mucosal absorption, respectively) by a compounding pharmacy for use by people with IH and related disorders. Read more about flumazenil on HF’s Treatment web page HERE; also, see HF's FAQs about Flumazenil Access.
  • Food and Drug Administration
    The United States Food and Drug Administration (FDA) is an agency within the U.S. Department of Health and Human Services. It is responsible for protecting the public health by ensuring the safety, effectiveness, quality, and security of human and veterinary drugs, vaccines, and other biologic products and medical devices. The FDA is also responsible for the safety and security of most of our nation’s food supply and of cosmetics.
  • FOSQ
    The Functional Outcomes of Sleep Questionnaire (FOSQ) was developed in 1997 as a means to measure the impact of excessive daytime sleepiness on a person’s daily ability to function. The 30 questions are divided into five subscales – activity level, vigilance, intimacy and sexual relationships, general productivity, and social outcomes. A shorter version, FOSQ-10, is also available; this shorter version contains only 10 questions.
  • Functional Outcomes of Sleep Questionnaire
    The Functional Outcomes of Sleep Questionnaire (FOSQ) was developed in 1997 as a means to measure the impact of excessive daytime sleepiness on a person’s daily ability to function. The 30 questions are divided into five subscales – activity level, vigilance, intimacy and sexual relationships, general productivity, and social outcomes. A shorter version, FOSQ-10, is also available; this shorter version contains only 10 questions.
  • g

  • GABA
    γ-Aminobutyric acid (Gamma-aminobutyric) or GABA is the main inhibitory neurotransmitter in the central nervous system (brain and spinal cord) of mammals. Its primary role is to reduce the excitability or dampen the actions of cells throughout the nervous system. In humans, GABA is also directly responsible for regulating muscle tone.
  • GABA-related hypersomnia
    GABA-related hypersomnia occurs in people who have one of the central disorders of hypersomnolence (idiopathic hypersomnia, Kleine-Levin syndrome, narcolepsy, or hypersomnia due to a medical or psychiatric disorder) and have the somnogen in their cerebrospinal fluid (CSF).
  • genome-wide association study
    A genome-wide association study (GWAS) is a study that looks at people’s complete genetic material in order to identify DNA markers. It then compares the markers from people with a disease or trait to the markers for people without the disease or trait.
  • genotype
    Your genotype is your complete heritable genetic identity; it is your unique genome that would be revealed by personal genome sequencing. However, the word genotype can also refer just to a particular gene or set of genes carried by an individual.” Read more HERE.
  • GWAS
    A genome-wide association study (GWAS) is a study that looks at people’s complete genetic material in order to identify DNA markers. It then compares the markers from people with a disease or trait to the markers for people without the disease or trait.
  • h

  • HF
    Hypersomnia Foundation, a nonprofit 501(c)(3) organization, dedicated to improving the lives of people with idiopathic hypersomnia and related disorders by advocating on their behalf, providing support, educating the public and healthcare professionals, raising awareness, and funding research into effective treatments, better diagnostic tools, and, ultimately, a cure for these debilitating conditions. Read more about our mission HERE.
  • histamine
    Histamine is a substance produced in the body that acts as a neurotransmitter. It is an important part of the reticular activating system (the part of the brain that wakes people up). Histamine may serve as a biomarker for problems or dysfunction in the hypothalamus. It is also involved in a number of other bodily processes, including the immune and inflammatory responses and the regulation of gut function.
  • HLA DQB1*0602
    The HLA, or human leukocyte antigen, system or complex is the gene complex that encodes for proteins on the surface of white blood cells. These cell-surface proteins are responsible for regulating our immune systems and our ability to fight infection. The HLA gene complex resides within chromosome 6. Most people with type 1 narcolepsy carry the HLA-DQB1*0602 gene, and are thus referred to as being “HLA-DQB1*0602 positive.” (Note: people with type 2 narcolepsy [or narcolepsy without cataplexy] often do not carry this gene).
  • HLA typing
    The HLA, or human leukocyte antigen, system or complex is the gene complex that encodes for proteins on the surface of white blood cells. These cell-surface proteins are responsible for regulating our immune systems and our ability to fight infection. HLA typing is a test that identifies human leukocyte antigens (HLA) in your system. While HLA typing is often conducted before numerous types of transplant/transfer surgeries (such as organ transplants and bone marrow transfers) to ensure compatibility between the prospective donor and the recipient, HLA typing is not an appropriate test (on its own) for diagnosing type 1 narcolepsy. This is because, even though most people with type 1 narcolepsy carry the HLA-DQB1*0602 gene, 20% of the general population carry this same gene, too.
  • humoral

    A humoral substance is a body fluid, or a substance related to a body fluid, especially with regard to immune responses involving antibodies in body fluids (as distinct from cells). Many of the bacteria that cause infectious diseases in humans multiply in the extracellular spaces of the body, and these extracellular spaces are protected by the humoral immune response, in which antibodies produced by B cells cause the destruction of extracellular microorganisms and prevent the spread of intracellular infections.

  • hypersexuality
    Hypersexuality is a clinical diagnosis used to describe increased or extremely frequent sexual urges or behavior.
  • hypersomnia
    Hypersomnia refers to the condition of sleeping excessive amounts. However, in current medical terminology, both “hypersomnia” and the related word “hypersomnolence” are used more broadly to indicate long sleep durations, excessive daytime sleepiness, or both. In some classification systems (such as the ICSD-3, which the HF follows), “hypersomnia” is reserved to refer to specific disease entities, such as idiopathic hypersomnia and the related sleep disorders, while “hypersomnolence” refers to the symptoms of long sleep and/or excessive daytime sleepiness regardless of cause. For more details, see Classification of Hypersomnias.
  • hypersomnolence
    Hypersomnolence refers to the symptoms of long sleep and/or excessive daytime sleepiness. For more details, see Classification of Hypersomnias.
  • hypersomnolence disorder
    In general, anyone who meets ICSD-3 criteria for IH would meet DSM-5 criteria for hypersomnolence disorder, but not vice versa. The ICSD-3 also requires objective diagnostic measurements (e.g., MSLT, extended EEG recordings) and longer sleep times (11+ hours of sleep in the ICSD-3 vs. 9+ hours in DSM-5). Read more About IH.
  • hypnagogic

    Hypnagogic is the transition from wakefulness to falling asleep.

  • hypnagogic hallucinations
    Hypnagogic or hypnopompic hallucinations are sensory experiences involving the apparent perception of something that is not present, that occur at the transition from wakefulness to sleep (hypnagogic) or from sleep to wakefulness (hypnopompic). These hallucinations are typically visual in nature, but can affect other forms of sensation, such as hearing or touch.
  • hypnopompic
    Hypnopompic refers to the transition from sleep to wakefulness.
  • hypocretin
    Hypocretin, also known as orexin, is a neurotransmitter that regulates alertness, mood, and appetite. Hypocretin/orexin was discovered almost at the same time by two different groups of researchers in the late 1990s. One of the groups, headed by Dr. Masashi Yanagisawa at the University of Texas Southwestern in Dallas, was working on obesity and named the neurotransmitter orexin (orexis is Greek for appetite). The other group, based at Harvard, named it hypocretin, because it is produced in the hypothalamus and somewhat resembles secretin, a hormone found in the gut. For now, the naming controversy continues — both camps are firmly entrenched in their terminology and neither will budge. Whatever its name, high levels of this neurotransmitter are associated with increased appetite, improved mood, and enhanced wakefulness. Low or nonexistent levels of hypocretin are found in the cerebrospinal fluid of people with type 1 narcolepsy.
  • hypothalamus
    The hypothalamus is a very small part of the brain that has a number of very important functions: it controls the autonomic nervous system and processes and secretes neurohormones. These hormones regulate body temperature, hunger, thirst, sleep, fatigue, sex drive, mood, sleep, alertness, and circadian rhythms.
  • hypothesis
    In science, a hypothesis is an idea or explanation that researchers then test in an experiment.
  • i

  • ICSD
    The International Classification of Sleep Disorders (ICSD) is the authoritative clinical text for the diagnosis of sleep disorders, published by the American Academy of Sleep Medicine. The 3rd edition, ICSD-3, was published in 2014, replacing ICSD-2 (which had replaced ICSD-1 in 2005). The ICSD-3 groups sleep disorders into six major categories – 1) insomnia, 2) sleep-related breathing disorders, 3) central disorders of hypersomnolence, 4) circadian rhythm sleep-wake disorders, 5) parasomnias, and 6) sleep-related movement disorders. A seventh category is for “other sleep disorders” not captured by the six major categories. Sleep disorders including idiopathic hypersomnia, narcolepsy (both types 1 and 2), and Kleine-Levin syndrome are categorized as “central disorders of hypersomnolence.”
  • idiopathic hypersomnia
    Idiopathic hypersomnia (IH) is a neurological disorder characterized by excessive daytime sleepiness (often with associated cognitive dysfunction), despite getting a full night’s sleep or longer. People with IH may also experience difficulty awakening, sleep drunkenness, automatic behaviors, and symptoms related to the autonomic nervous system, such as feeling lightheaded when standing up quickly. Read more About IH.
  • IH
    Idiopathic hypersomnia (IH) is a neurological disorder characterized by excessive daytime sleepiness (often with associated cognitive dysfunction), despite getting a full night’s sleep or longer. People with IH may also experience difficulty awakening, sleep drunkenness, automatic behaviors, and symptoms related to the autonomic nervous system, such as feeling lightheaded when standing up quickly. Read more About IH.
  • in vitro
    In vitro means that something — for example, an experiment — takes place outside the body in an artificial environment.
  • inhibitory
    Inhibitory means hindering or preventing an action. For example, inhibitory neurotransmitters, such as GABA and serotonin, decrease the likelihood that a nerve cell will send its chemical message on to the next nerve cell.
  • International Classification of Sleep Disorders
    The International Classification of Sleep Disorders (ICSD) is the authoritative clinical text for the diagnosis of sleep disorders, published by the American Academy of Sleep Medicine. The 3rd edition, ICSD-3, was published in 2014, replacing ICSD-2 (which had replaced ICSD-1 in 2005). The ICSD-3 groups sleep disorders into six major categories – 1) insomnia, 2) sleep-related breathing disorders, 3) central disorders of hypersomnolence, 4) circadian rhythm sleep-wake disorders, 5) parasomnias, and 6) sleep-related movement disorders. A seventh category is for “other sleep disorders” not captured by the six major categories. Sleep disorders including idiopathic hypersomnia, narcolepsy (both types 1 and 2), and Kleine-Levin syndrome are categorized as “central disorders of hypersomnolence.”
  • k

  • Kleine-Levin syndrome
    Kleine-Levin syndrome (KLS) is a rare disorder in which affected people experience episodes at least once per year during which they sleep for at least 11 hours out of every day (but often for days at a time), eat excessively (megaphagia), have abnormal thinking and behavior, and are hypersexual. Between episodes, their alertness, behavior, and thinking are normal. Read more About Related Sleep Disorders.
  • KLS
    Kleine-Levin syndrome (KLS) is a rare disorder in which affected people experience episodes at least once per year during which they sleep for at least 11 hours out of every day (but often for days at a time), eat excessively (megaphagia), have abnormal thinking and behavior, and are hypersexual. Between episodes, their alertness, behavior, and thinking are normal. Read more About Related Sleep Disorders.
  • knockout mouse
    A knockout mouse is a mouse in which researchers have inactivated, or "knocked out," an existing gene in the animal by replacing the gene or disrupting it with a different piece of DNA.
  • l

  • LC-MS

    Liquid chromatography-mass spectrometry (LC-MS) is a chemical analysis technique used to separate, identify, measure, and analyze substances in a mixture. It combines the physical separation capabilities of liquid chromatography with the mass analysis capabilities of mass spectrometry. (While liquid chromatography separates the individual components of a mixture, mass spectrometry ionizes atoms or molecules to facilitate their separation and detection in accordance with their molecular masses and charges.) This tandem technique is used in a variety of fields, including biotechnology, pharmaceutical research and food processing, especially when the mixture is highly complex.

  • lead compound
    A lead compound is a peptide, small molecule, or other agent with pharmacological or biochemical properties, which may have therapeutic potential and value as a starting point for drug development.
  • levothyroxine
    Levothyroxine (Synthroid, Tirosint, Unithroid, Levo-T, Levoxyl) is an FDA-approved thyroid medication that replaces a hormone normally produced by the thyroid gland to regulate the body’s energy and metabolism. It is generally prescribed for people with hypothyroidism (an underactive thyroid gland), and while it has been suggested as a possible treatment for idiopathic hypersomnia, levothyroxine carries potential risks, including the risk of cardiac arrhythmia. Read more about levothyroxine at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • liquid chromatography-mass spectrometry

    Liquid chromatography-mass spectrometry (LC-MS) is a chemical analysis technique used to separate, identify, measure, and analyze substances in a mixture. It combines the physical separation capabilities of liquid chromatography with the mass analysis capabilities of mass spectrometry. (While liquid chromatography separates the individual components of a mixture, mass spectrometry ionizes atoms or molecules to facilitate their separation and detection in accordance with their molecular masses and charges.) This tandem technique is used in a variety of fields, including biotechnology, pharmaceutical research and food processing, especially when the mixture is highly complex.

  • longitudinal
    In a longitudinal study, researchers observe the same subjects and repeatedly gather data, or information, over a period of time.
  • LP
    A lumbar puncture (or LP) is a medical procedure in which a needle is inserted through the skin of the lower back between two vertebrae, or bones of the spinal column, into the spinal canal. A sample of the cerebrospinal fluid is then removed and sent to a laboratory for testing.
  • lumbar puncture
    A lumbar puncture (or LP) is a medical procedure in which a needle is inserted through the skin of the lower back between two vertebrae, or bones of the spinal column, into the spinal canal. A sample of the cerebrospinal fluid is then removed and sent to a laboratory for testing.
  • m

  • MAB
    The Hypersomnia Foundation’s Medical Advisory Board. Read more HERE.
  • magnetic resonance imaging
    MRI (magnetic resonance imaging) uses strong magnets and radio waves housed inside a specialized machine or scanner to make detailed 3-D pictures or images of organs and tissues within the body.
  • Maintenance of Wakefulness Test
    The purpose of the Maintenance of Wakefulness Test (MWT) is to see if you are able to stay awake during the daytime. The MWT takes place in a darkened, quiet, comfortable room. A technician places sensors on your head, face, and neck that can measure sleep. You recline in bed and try to stay awake during each of four measurement periods. The four measurement periods start about 9 or 10 am and last 40 minutes each. If you fall asleep, you are allowed to sleep for 90 seconds and are then awakened and kept awake until the next measurement period. If you don’t fall asleep within 40 minutes, that measurement period is ended. The measurement periods typically take place every two hours. This test is similar to the Multiple Sleep Latency Test (MSLT), but the MWT measures your likelihood of falling asleep when you are trying to stay awake. This is a subtle but important difference. Most people without sleep problems are able to stay awake for at least the first 8 minutes of each measurement period.
  • mazindol
    Mazindol is a stimulant that works similarly to amphetamines, in that it increases alertness and central nervous system stimulation, but, unlike amphetamines, it has little or no effect on mood or the cardiovascular system. It has dopamine and adrenergic blocking properties, and has been shown to be effective for the treatment of both excessive daytime sleepiness and cataplexy in humans, and in canine narcolepsy. While mazindol is not currently approved in the U.S., it was granted Orphan Drug Designation (ODD) status for the treatment of narcolepsy by the U.S. FDA in 2016, and granted ODD status by the European Commission in 2015. Read more about mazindol on HF’s Treatments page HERE.
  • megaphagia
    Megaphagia, also referred to as polyphagia or hyperphagia, is an excessive appetite or hunger and abnormally large intake of solid food.
  • melatonin
    Melatonin is a hormone that the body produces to regulate sleep. The production and release of melatonin is connected to the time of day – increasing when it is dark outside and decreasing when it is light. Melatonin production gradually decreases with age, and melatonin is available as a supplement, usually in the form of an oral tablet. It is often used to combat jet lag or insomnia, although one small study found that melatonin taken at bedtime relieved excessive daytime sleepiness in 50% of participants. Read more about methylphenidate at FamilyDoctor.org HERE and on HF’s Treatment web page HERE.
  • messenger RNA
    Messenger RNA (mRNA) is a subtype of RNA. An mRNA molecule is created during transcription to carry a portion of the DNA code (genetic information) to the ribosome (the site in the cell where proteins are made).
  • metabolite
    A metabolite is any substance produced during digestion or other chemical processes that occur in the body. Metabolite may also refer to the product that remains after a drug is broken down by the body.
  • methylphenidate
    Methylphenidate (Ritalin, Ritalin SR, Concerta, Daytrana, Quillivant XR, Aptensio XR, QuilliChew ER, Metadate ER, Cotempla XR-ODT, Methylin) is a central nervous stimulant medication used to treat attention deficit hyperactivity disorder (ADHD) and narcolepsy. It may be taken by mouth or applied to the skin. It works by changing the amounts of certain natural substances in the brain. Read more about methylphenidate at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • modafinil
    Modafinil (Provigil, Alertec, Modavigil) is a non-stimulant, wake-promoting drug that is approved by the U.S. FDA to improve wakefulness in adult patients with excessive sleepiness associated with narcolepsy, obstructive sleep apnea, and shift work disorder. It is similar to armodafinil (Nuvigil), another non-stimulant, wake-promoting medication. Modafinil has been studied in two placebo-controlled trials that included people with IH, and has been shown to help with sleepiness in people with IH. However, both modafinil and armodafinil can interact with hormonal birth control to make it less effective (learn more HERE) and can result in a threatening rash. In addition, modafinil and armodafinil can sometimes result in headaches which, if severe enough, can cause a user to reduce the dosage, thereby limiting the effectiveness of the medications. Read more about modafinil at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • MRI
    MRI (magnetic resonance imaging) uses strong magnets and radio waves housed inside a specialized machine or scanner to make detailed 3-D pictures or images of organs and tissues within the body.
  • mRNA
    Messenger RNA (mRNA) is a subtype of RNA. An mRNA molecule is created during transcription to carry a portion of the DNA code (genetic information) to the ribosome (the site in the cell where proteins are made).
  • MSLT
    The Multiple Sleep Latency Test (MSLT) measures how quickly you fall asleep in a quiet environment during the day. The MSLT typically consists of five scheduled naps, each nap opportunity lasting 20 minutes, separated by two-hour breaks. During each of the nap opportunities, you lie in bed in a darkened, quiet room and try to go to sleep. The time that it takes you to fall asleep is called the sleep latency. You will be allowed to sleep for a maximum of 15 minutes during each opportunity. (You will be awakened if you don’t wake up on your own). If you do not fall asleep within 20 minutes, the nap trial will end.
  • Multiple Sleep Latency Test
    The Multiple Sleep Latency Test (MSLT) measures how quickly you fall asleep in a quiet environment during the day. The MSLT typically consists of five scheduled naps, each nap opportunity lasting 20 minutes, separated by two-hour breaks. During each of the nap opportunities, you lie in bed in a darkened, quiet room and try to go to sleep. The time that it takes you to fall asleep is called the sleep latency. You will be allowed to sleep for a maximum of 15 minutes during each opportunity. (You will be awakened if you don’t wake up on your own). If you do not fall asleep within 20 minutes, the nap trial will end.
  • MWT
    The purpose of the Maintenance of Wakefulness Test (MWT) is to see if you are able to stay awake during the daytime. The MWT takes place in a darkened, quiet, comfortable room. A technician places sensors on your head, face, and neck that can measure sleep. You recline in bed and try to stay awake during each of four measurement periods. The four measurement periods start about 9 or 10 am and last 40 minutes each. If you fall asleep, you are allowed to sleep for 90 seconds and are then awakened and kept awake until the next measurement period. If you don’t fall asleep within 40 minutes, that measurement period is ended. The measurement periods typically take place every two hours. This test is similar to the Multiple Sleep Latency Test (MSLT), but the MWT measures your likelihood of falling asleep when you are trying to stay awake. This is a subtle but important difference. Most people without sleep problems are able to stay awake for at least the first 8 minutes of each measurement period.
  • n

  • narcolepsy
    Narcolepsy is a chronic neurological disorder that affects the brain’s ability to control sleep and wakefulness. The most typical symptoms are excessive daytime sleepiness, cataplexy, sleep paralysis, and hypnagogic or hypnopompic hallucinations. Additional symptoms of narcolepsy include fragmented sleep and insomnia, and automatic behaviors. Unlike people with IH, people with narcolepsy generally feel refreshed after taking a nap. There are two types of narcolepsy – type 1 narcolepsy (in which a person either has low levels of a brain hormone [hypocretin] or has cataplexy), and type 2 narcolepsy (in which a person does not have cataplexy or low hypocretin). Read more HERE.
  • NDRIs
    NDRIs (norepinephrine-dopamine reuptake inhibitors) are medications that block the reabsorption (reuptake) of specific neurotransmitters (norepinephrine and dopamine) after they have been excreted from a nerve cell. This inhibition of the reabsorption results in more activity of these specific neurotransmitters throughout the brain. NDRIs are commonly used to treat clinical depression, ADHD and narcolepsy. NDRI medications approved for use in the U.S. include methylphenidate (Ritalin), bupropion (Wellbutrin) and solriamfetol (Sunosi).
  • neocortex
    If you look at a human or mammal’s brain from the top or the sides, what you see is the neocortex. In humans, this part of the brain, which is about 2-4 mm thick (a thickness somewhere between the size of the point of a crayon and the eraser end of a pencil), forms ridges or deep grooves called sulci. The neocortex in humans controls sensory perception, generation of motor commands, spatial reasoning, conscious thought, and language.
  • neuroendocrine
    Neuroendocrine means both neural and endocrine in structure and function. Neuroendocrine cells are like nerve cells (neurons), but they also make hormones, like cells of the endocrine system (endocrine cells) do. Neuroendocrine cells receive neuronal input (neurotransmitters released by nerve cells) and, as a result of this input, release hormones into the bloodstream.
  • neuromodulator
    A neuromodulator is a chemical substance released from a neuron in the central nervous system (the brain or spinal cord), or in the periphery, that transmits information to other neurons, altering their activities. A neuromodulator affects not just a single cell, but groups of neurons or effector cells that have the appropriate receptors. Unlike a neurotransmitter, it may be released at sites other than synaptic sites, it often acts through second messengers, and it can produce long-lasting effects. The release may be local, so that only nearby neurons or effectors are influenced, or it may be more widespread.
  • neuron
    A neuron is simply a nerve cell. Neurons are specialized cells in the nervous system that transmit information to other nerve cells, muscle cells or gland cells.
  • neurotransmitter
    A neurotransmitter is a chemical “messenger” that allows nerve cells to “talk” with other nerve cells and with muscles, organs or other tissue. This chemical is released from one nerve cell, or neuron, at a specialized location (synaptic site), or junction. It then spreads, or diffuses, across a narrow gap, or cleft, to affect one or sometimes two other neurons on the other side of the cleft (postsynaptic), a muscle cell or another effector cell. A neurotransmitter influences a neuron in one of 3 ways: excitatory, inhibitory or modulatory.
  • non-rapid-eye-movement sleep
    Non-rapid-eye-movement sleep (NREM sleep) consists of sleep stages 1, 2 and 3, which typically makes up about 75% of your time asleep, while the REM stage makes up the other 25% of sleep. Read more about sleep stages HERE.
  • norepinephrine
    Norepinephrine a neurotransmitter that is responsible for mobilizing the brain and body for action, increasing focus, alertness and the retrieval of memory.
  • norepinephrine-dopamine reuptake inhibitors
    NDRIs (norepinephrine-dopamine reuptake inhibitors) are medications that block the reabsorption (reuptake) of specific neurotransmitters (norepinephrine and dopamine) after they have been excreted from a nerve cell. This inhibition of the reabsorption results in more activity of these specific neurotransmitters throughout the brain. NDRIs are commonly used to treat clinical depression, ADHD and narcolepsy. NDRI medications approved for use in the U.S. include methylphenidate (Ritalin), bupropion (Wellbutrin) and solriamfetol (Sunosi).
  • norepinephrine reuptake inhibitors
    NRIs (norepinephrine reuptake inhibitors) are medications that work by blocking the action of the norepinephrine transporter (NET). NRIs are commonly used to treat major depressive disorder (MDD), anxiety, panic disorder, narcolepsy, and ADHD. NRI medications approved for use in the U.S. include atomoxetine (Strattera). Although NRIs are sometimes noted to be selective NRIs, this term is not to be confused with SNRIs (serotonin and norepinephrine reuptake inhibitors).
  • NREM sleep
    Non-rapid-eye-movement sleep (NREM sleep) consists of sleep stages 1, 2 and 3, which typically makes up about 75% of your time asleep, while the REM stage makes up the other 25% of sleep. Read more about sleep stages HERE.
  • NRIs
    NRIs (norepinephrine reuptake inhibitors) are medications that work by blocking the action of the norepinephrine transporter (NET). NRIs are commonly used to treat major depressive disorder (MDD), anxiety, panic disorder, narcolepsy, and ADHD. NRI medications approved for use in the U.S. include atomoxetine (Strattera). Although NRIs are sometimes noted to be selective NRIs, this term is not to be confused with SNRIs (serotonin and norepinephrine reuptake inhibitors).
  • nucleotide
    A nucleotide is one of the structural components, or building blocks, of DNA and RNA. A nucleotide consists of one of four chemicals (adenine, thymine, guanine or cytosine), plus a molecule of sugar and a molecule of phosphoric acid.
  • o

  • obstructive sleep apnea
    Obstructive sleep apnea (OSA) is a sleep disorder characterized by repetitive partial and/or complete collapses of the upper airway, associated with arousals/awakenings and/or decreases in oxygen levels in the blood. The episodes last more than 10 seconds, by definition, but can last up to 30-60 seconds. Untreated sleep apnea may cause daytime sleepiness and increased risk of cardiovascular events, such as high blood pressure, heart attack and stroke.
  • ODD
    Orphan Drug Designation (ODD) in the U.S. means that a drug has been designated by the U.S. FDA as an "orphan drug" pursuant to the Orphan Drug Act of 1983. This law was passed to facilitate the development of drugs for rare diseases that affect small numbers of people living in the U.S. (which is defined as affecting less than 200,000 people in the U.S.). Orphan drug designation does not mean that the drug is safe or effective, and does not mean that it is legal to market or sell the drug in the U.S. Rather, the designation means only that the drug's sponsor qualifies for certain benefits from the U.S. government, including tax incentives and market exclusivity for 7 years. Orphan drugs normally follow the same regulatory approval process as other drugs (including dosing, safety and efficacy). However, some statistical requirements are lessened (such as not requiring the same number of patients in a Phase III clinical trial as would be required for a non-orphan drug), in order to try to provide a more streamlined process for gaining ultimate approval. Japan adopted a similar law in 1993; the European Union adopted a similar law in 2000.
  • off-label
    The term “off-label” means that a drug is prescribed for a condition other than that for which it has been officially approved.
  • Orphan Drug Designation
    Orphan Drug Designation (ODD) in the U.S. means that a drug has been designated by the U.S. FDA as an "orphan drug" pursuant to the Orphan Drug Act of 1983. This law was passed to facilitate the development of drugs for rare diseases that affect small numbers of people living in the U.S. (which is defined as affecting less than 200,000 people in the U.S.). Orphan drug designation does not mean that the drug is safe or effective, and does not mean that it is legal to market or sell the drug in the U.S. Rather, the designation means only that the drug's sponsor qualifies for certain benefits from the U.S. government, including tax incentives and market exclusivity for 7 years. Orphan drugs normally follow the same regulatory approval process as other drugs (including dosing, safety and efficacy). However, some statistical requirements are lessened (such as not requiring the same number of patients in a Phase III clinical trial as would be required for a non-orphan drug), in order to try to provide a more streamlined process for gaining ultimate approval. Japan adopted a similar law in 1993; the European Union adopted a similar law in 2000.
  • OSA
    Obstructive sleep apnea (OSA) is a sleep disorder characterized by repetitive partial and/or complete collapses of the upper airway, associated with arousals/awakenings and/or decreases in oxygen levels in the blood. The episodes last more than 10 seconds, by definition, but can last up to 30-60 seconds. Untreated sleep apnea may cause daytime sleepiness and increased risk of cardiovascular events, such as high blood pressure, heart attack and stroke.
  • oxidation

    Oxidation is the chemical process by which oxygen combines with an element, causing the element to undergo a change. Specifically, oxidation is the loss of electrons – it occurs whenever an element is combined with oxygen, thereby giving away electrons. [Common examples of oxidation are (1) when iron reacts with oxygen, and changes the iron to rust, and (2) when cut fruit is exposed to oxygen and turns brown.)] Sleep researchers have examined whether people with narcolepsy symptoms might have reduced oxidation of their fatty acids, which are vital for cellular energy. Some of these researchers have advocated for L-carnitine supplementation in order to increase this fatty acid oxidation in people with narcolepsy.

  • p

  • PAAC
    The PAAC is the Hypersomnia Foundation's Patient Advisory and Advocacy Council (PAAC). This council consists of patient and supporter volunteers who meet monthly by phone conference to offer feedback to HF and share the needs of the hypersomnia community. They play a very valuable role for HF and the hypersomnia community at large. Interested in joining the PAAC? It requires commitment to a monthly conference call, with possible email correspondence in-between. Members have IH or a related sleep disorder, or have a loved one with one of these rare disorders. The group is small so that all members can join in the discussion, and members typically rotate after a period of time. If you are interested in volunteering, please send an email to with the subject line “PAAC.”
  • periprocedural
    Periprocedural means occurring soon before, during, or soon after the performance of a medical procedure, such as a surgery.
  • PET
    A positron emission tomography (PET) scan creates computerized images of chemical changes that take place in tissue. In this test, various radioactive materials (tracers) and substances are injected into patients’ veins. The patient is then scanned in a special machine or scanner. Radiologists can then identify activity in certain parts of the brain by measuring blood flow and oxygen and glucose metabolism in the tissues of the working brain.
  • phenotype
    A phenotype is a physical appearance, such as height, or a biochemical characteristic, such as blood type, of an organism. Most phenotypes are influenced by both genotype and the environment. Read more HERE.
  • pitolisant
    Pitolisant (Wakix) is a non-stimulant wake-promoting medication that was approved in August 2019 by the FDA and approved in 2016 in Europe. It is a selective histamine 3 (H3) receptor antagonist/inverse agonist that works through a novel mechanism of action to increase the synthesis and release of histamine, a wake-promoting neurotransmitter in the brain. Read more about pitolisant on HF’s Treatment web page HERE.
  • placebo
    A placebo is an inactive (or sham) substance that is designed to look like the substance or drug that is being studied. A placebo is used as a control in clinical trials and does not contain any active materials.
  • placebo-controlled
    A placebo-controlled trial or study is one in which the effect of a drug is compared with the effect of a placebo. In placebo-controlled trials, participants receive either the drug being studied or a placebo. The results of the drug group and the placebo group are then compared to see if the drug is more effective in treating the condition than is the placebo.
  • polysomnography
    Polysomnography (PSG), also called a sleep study, uses multiple electrodes and devices (multi-channel) to gather information about a patient during sleep. A standard in-laboratory study records brain waves, eye movements, oxygen levels in the blood, jaw movement, heart rate, breathing rate, airflow, respiratory effort, sound, and limb movements. Taken as a total picture, the results of these recordings allow a calculation of sleep stages and provide data that can help diagnose disorders of sleep. In contrast, limited-channel sleep studies usually take place outside of the sleep laboratory.
  • positron emission tomography
    A positron emission tomography (PET) scan creates computerized images of chemical changes that take place in tissue. In this test, various radioactive materials (tracers) and substances are injected into patients’ veins. The patient is then scanned in a special machine or scanner. Radiologists can then identify activity in certain parts of the brain by measuring blood flow and oxygen and glucose metabolism in the tissues of the working brain.
  • postural orthostatic tachycardia syndrome
    Postural orthostatic tachycardia syndrome (POTS), also known as postural tachycardia syndrome, is a disorder of the autonomic nervous system characterized by an excessive increase in heart rate upon standing.
  • POTS
    Postural orthostatic tachycardia syndrome (POTS), also known as postural tachycardia syndrome, is a disorder of the autonomic nervous system characterized by an excessive increase in heart rate upon standing.
  • PSG
    Polysomnography (PSG), also called a sleep study, uses multiple electrodes and devices (multi-channel) to gather information about a patient during sleep. A standard in-laboratory study records brain waves, eye movements, oxygen levels in the blood, jaw movement, heart rate, breathing rate, airflow, respiratory effort, sound, and limb movements. Taken as a total picture, the results of these recordings allow a calculation of sleep stages and provide data that can help diagnose disorders of sleep. In contrast, limited-channel sleep studies usually take place outside of the sleep laboratory.
  • psychomotor vigilance task
    The Psychomotor Vigilance Task (PVT) is a tool used to measure sustained attention and alertness. It measures the speed with which subjects respond to a visual stimulus. In the most common PVT tasks, an individual must press a button in response to a light appearing randomly on a handheld device.
  • PVT
    The Psychomotor Vigilance Task (PVT) is a tool used to measure sustained attention and alertness. It measures the speed with which subjects respond to a visual stimulus. In the most common PVT tasks, an individual must press a button in response to a light appearing randomly on a handheld device.
  • PWH
    PWH is an acronym for a person with a hypersomnia (or people with hypersomnias).
  • PWIH
    PWIH is an acronym for a person (or people) with idiopathic hypersomnia.
  • PWN
    PWN is an acronym for a person (or people) with narcolepsy.
  • r

  • randomized
    In a randomized controlled clinical trial, participants or subjects are assigned randomly (i.e., by chance) to separate groups that receive different treatments or other interventions. Using chance to divide people into groups means that the groups will be similar and that the effects of the treatments they receive can be compared more fairly.
  • reboxetine
    Reboxetine (Davedex, Edronax, Irenor, Norebox, Prolift, Solvex, Yeluoshu, Zuolexin) belongs to a group of medicines called norepinephrine reuptake inhibitors (NRIs), and is marketed as an antidepressant for the use in the treatment of major depression. Reboxetine is very similar to atomoxetine. Although reboxetine is approved for use in Europe and elsewhere, it is not currently approved in the U.S. However, in October 2018, the U.S. FDA granted Orphan Drug Designation (ODD) status to Axsome Therapeutics’ AXS-12 (reboxetine) for the treatment of narcolepsy symptoms. Read more about reboxetine on HF’s Treatment web page HERE.
  • related sleep disorder
    In people with certain disorders other than IH, excessive daytime sleepiness and/or long sleep times are commonly present and can be very similar to that seen in idiopathic hypersomnia. These disorders include narcolepsy types 1 and 2, Kleine-Levin syndrome, and hypersomnias associated with certain other disorders. Because current treatments for these disorders are very similar, and current research indicates that there may  be significant overlap among them, it is important to address and research them together. For more details, please see About Related Sleep Disorders and Classification of Hypersomnias.
  • REM sleep
    Rapid eye movement (REM) sleep is one of the two basic states of sleep. REM sleep, also known as dream sleep, is characterized by rapid eye movements and more irregular breathing and heart rate compared to non-REM (NREM) sleep, the other basic state of sleep (which has several numbered stages).
  • research study
    Research studies include clinical studies, which include clinical trials and observational clinical studies (with human participants). However, research studies may also involve animals, basic research at the cellular level, or other types of research that do not involve the testing of treatments or other interventions in people. New treatments are first tested in animals or in other ways before being tried in humans. Read more HERE.
  • ribosome
    A ribosome is a minute particle that is present in large numbers in all living cells. It serves as the site in the cell where proteins are made.
  • ritanserin
    Ritanserin is a serotonin receptor antagonist which has been shown in humans to increase deep slow-wave sleep and to improve symptoms in a variety of psychiatric disorders, including OCD, acute mania, and schizophrenia. While it is not currently available in the U.S., it is available in Europe. In a 2003 study of 134 persons with narcolepsy, adding ritanserin to their usual narcolepsy treatment resulted in a significant increase in nocturnal slow-wave deep sleep and significantly reduced non-REM Stage 1 percentage during daytime sleep. Read more about ritanserin on HF’s Treatment web page HERE.
  • s

  • SAB
    The Hypersomnia Foundation’s Scientific Advisory Board. Read more HERE.
  • selective serotonin reuptake inhibitors
    SSRIs (selective serotonin reuptake inhibitors) work by limiting, rather than blocking, the serotonin transporter (SERT). Essentially they work by increasing the levels of serotonin in the brain. They are typically used to treat MDD and anxiety disorders. SSRI medications approved for use in the U.S. include fluoxetine (Prozac) and sertraline (Zoloft).
  • selegiline
    Selegiline (Emsam, Eldepryl, Zelapar) is in a group of medications called monoamine oxidase type B (MAO-B) inhibitors, which means that it works by slowing the breakdown of certain substances in the brain (mostly dopamine). Selegiline was approved by the U.S. FDA in 1989 for the treatment of Parkinson’s disease, to help control the difficulties with movement, muscle control and balance. Even though selegiline has been reported to decrease excessive daytime sleepiness, it is usually not prescribed for narcolepsy because of the high dosage required. Read more about selegiline at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • sensitivity
    The sensitivity of a diagnostic test indicates how often the test will be positive if a person truly has the disease (true positive rate). In other words, if the test is highly sensitive and the test result is negative, you can be nearly certain that the person doesn’t have the disease for which they’re being tested. A sensitive test helps rule out disease (when the result is negative). Read more HERE.
  • serotonin-norepinephrine reuptake inhibitors
    SNRIs (serotonin-norepinephrine reuptake inhibitors) are medications that block the reabsorption (reuptake) of the neurotransmitters serotonin and norepinephrine in the brain. Most SNRIs treat depression, anxiety and long-term pain (especially nerve pain). SNRIs approved for use in the U.S. include desvenlafaxine (Pristiq), duloxetine (Cymbalta) and Venlafaxine (Effexor XR).
  • SF-36
    The SF-36 (or Short-Form Health Survey) is a questionnaire developed by RAND as a part of the Medical Outcomes Study to explain variations in patient outcomes. It is a 36-item, patient-reported survey of generic, coherent, and easily administered quality-of-life questions. The SF-36 is made up of eight scales that are summed to reach the total score. These scales include vitality, physical functioning, bodily pain, general health perceptions, physical role functioning, emotional role functioning, social role functioning, and mental health. The SF-36 does not include a scale to assess sleep.
  • single nucleotide polymorphism
    A single nucleotide polymorphism (SNP) is a DNA variation in which one nucleotide (the building block of DNA) differs from what is generally observed in the population. SNPs occur normally throughout a person’s DNA — usually about once in every 300 nucleotides. These variations are typically found in the DNA between genes. They can act as markers, helping scientists locate genes that are associated with a specific disease. When SNPs appear within a gene or in a regulatory region near a gene, they may play a more direct role in disease by affecting the function of a gene.
  • single-photon emission computed tomography
    Single-photon emission computed tomography (SPECT) is similar to positron emission tomography (PET) in that it uses a radioactive substance (tracer) and a special camera to create 3-D pictures of an internal organ of the body. Like PET, SPECT is particularly useful for looking at blood flow to an organ, such as the heart or brain. The primary difference between the two tests is that the tracers used in SPECT last longer than those used in PET, allowing for a longer time to view the organ at work.
  • sleep diary

    A sleep diary is a record of your sleep patterns, including the time you go to sleep and wake up, over an extended period of time (usually at least two weeks). A sleep diary can be extremely useful in helping doctors make a diagnosis of a sleep disorder or make a better determination of whether to refer a person for a sleep study.

  • sleep drunkenness
    Sleep drunkenness (i.e., severe sleep inertia) is an extreme and prolonged difficulty fully awakening, associated with an uncontrollable desire to go back to sleep, which can be accompanied by automatic behavior (performing tasks without conscious self-control and not remembering what or if it was done), disorientation, confusion, irritability, and poor coordination.
  • sleep efficiency
    Sleep efficiency is the percentage of time spent asleep while in bed. It is calculated by dividing the amount of time spent asleep (in minutes) by the total amount of time in bed (in minutes). A normal sleep efficiency is considered to be 85% or higher.
  • sleep inertia
    Sleep inertia includes feelings of grogginess and sleepiness that occur upon awakening, which can result in impaired alertness and may interfere with the ability to perform mental or physical tasks. A form of severe sleep inertia, commonly found in idiopathic hypersomnia, is called sleep drunkenness.
  • sleep latency
    Sleep latency is the amount of time it takes for a person to go from being fully awake to being asleep.
  • sleep onset REM period
    Sleep onset REM periods (SOREMPs) are REM sleep periods that occur within 15 minutes of sleep onset. SOREMPs are considered to support the diagnosis of narcolepsy.
  • sleep paralysis

    Sleep paralysis is a transitional state between wakefulness and sleep, in which one is aware but cannot move, speak, or react.

  • sleep stages
    Sleep is made up of four stages – stages 1, 2, 3 and REM (rapid eye movement). Stages 1, 2 and 3 are generally non-rapid-eye-movement (NREM), which typically makes up about 75% of your time asleep, while the REM stage makes up the other 25% of sleep. As you progress from wakefulness to deep sleep, you usually pass through progressively deeper stages, from stage 1 (the lightest) to stage 3, or slow wave sleep (the deepest stage, in which critical substances, such as human growth hormone, are released), and finally into REM sleep (during which the body doesn’t move and dreaming occurs). It is not uncommon for a person to move back and forth between stages 2 and 3 before moving into REM sleep. A typical 4-stage sleep cycle lasts about 90-110 minutes, and then the sleep cycle repeats with Stage 1. More stage 3 sleep occurs earlier in the sleep period, while more REM sleep occurs later in the sleep period. For example, the first period of REM sleep generally lasts about 10 minutes, with each later REM stage getting longer – and the final REM stage may last up to an hour.
  • SNP
    A single nucleotide polymorphism (SNP) is a DNA variation in which one nucleotide (the building block of DNA) differs from what is generally observed in the population. SNPs occur normally throughout a person’s DNA — usually about once in every 300 nucleotides. These variations are typically found in the DNA between genes. They can act as markers, helping scientists locate genes that are associated with a specific disease. When SNPs appear within a gene or in a regulatory region near a gene, they may play a more direct role in disease by affecting the function of a gene.
  • SNRIs
    SNRIs (serotonin-norepinephrine reuptake inhibitors) are medications that block the reabsorption (reuptake) of the neurotransmitters serotonin and norepinephrine in the brain. Most SNRIs treat depression, anxiety and long-term pain (especially nerve pain). SNRIs approved for use in the U.S. include desvenlafaxine (Pristiq), duloxetine (Cymbalta) and Venlafaxine (Effexor XR).
  • sodium oxybate
    Sodium oxybate (Xyrem) is a medication taken at bedtime (and usually again during the night) that promotes deep sleep and improves daytime sleepiness in people with narcolepsy (although its effects in those with idiopathic hypersomnia are not as well characterized). It was approved by the U.S. FDA in 2002 for both cataplexy and excessive daytime sleepiness (the first generic version was approved in 2017). It is a central nervous system depressant, and is the sodium salt of gamma hydroxybutyric (GHB) which is an endogenous compound and a metabolite of the neurotransmitter GABA. Read more about sodium oxybate at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • solriamfetol
    Solriamfetol (Sunosi) is a non-stimulant wake-promoting medication that was approved in March 2019 by the U.S. FDA for the treatment of sleepiness caused by narcolepsy and obstructive sleep apnea. It is the first dual-acting dopamine and norepinephrine reuptake inhibitor (NDRI) approved to treat excessive daytime sleepiness in adults. Read more about solriamfetol at MedlinePlus.gov HERE and on HF’s Treatment web page HERE.
  • somnogen

    A somnogen is any substance that causes or induces sleepiness.

  • SOREMP
    Sleep onset REM periods (SOREMPs) are REM sleep periods that occur within 15 minutes of sleep onset. SOREMPs are considered to support the diagnosis of narcolepsy.
  • specificity
    The specificity of a diagnostic test indicates how often the test will be negative if a person does not have the disease (true negative rate). In other words, if the test result for a highly specific test is positive, you can be nearly certain that the person actually has the disease for which they’re being tested. A very specific test rules in disease with a high degree of confidence. Read more HERE.
  • SPECT
    Single-photon emission computed tomography (SPECT) is similar to positron emission tomography (PET) in that it uses a radioactive substance (tracer) and a special camera to create 3-D pictures of an internal organ of the body. Like PET, SPECT is particularly useful for looking at blood flow to an organ, such as the heart or brain. The primary difference between the two tests is that the tracers used in SPECT last longer than those used in PET, allowing for a longer time to view the organ at work.
  • SSRIs
    SSRIs (selective serotonin reuptake inhibitors) work by limiting, rather than blocking, the serotonin transporter (SERT). Essentially they work by increasing the levels of serotonin in the brain. They are typically used to treat MDD and anxiety disorders. SSRI medications approved for use in the U.S. include fluoxetine (Prozac) and sertraline (Zoloft).
  • striatum
    The striatum is a section of the brain that lies beneath the front part of the cortex. This area of the brain has a number of functions, including planning and executing movement and controlling the reward system. The striatum looks as if it has grey and white stripes, and thus the name striae or stripe.
  • susceptibility gene
    A susceptibility gene is a permanent change in a gene (mutation) that increases a person’s susceptibility to or likelihood of developing a certain disease or disorder. When such a mutation is passed from a biological parent to a child, symptoms of the disease or disorder are more likely to occur, but it is not certain that the symptoms will occur.
  • t

  • T1N
    The International Classification of Sleep Disorders, third edition, divides narcolepsy into type 1 and type 2 (the previous edition used the terms narcolepsy with and without cataplexy). The new criteria for T1N require a combination of hypersomnolence and either low hypocretin levels in the cerebrospinal fluid or cataplexy plus short average sleep latency (≤ 8 minutes) and 2 or more sleep-onset REM periods (SOREMPs) on the Multiple Sleep Latency Test (MSLT). A SOREMP (within 15 minutes) of sleep onset on polysomnography (or PSG, a sleep study) may replace one of the SOREMPs on the MSLT. Read more About Related Sleep Disorders.
  • T2N
    The International Classification of Sleep Disorders, third edition, divides narcolepsy into type 1 and type 2 (the previous edition used the terms narcolepsy with and without cataplexy). Type 2 narcolepsy refers to narcolepsy without cataplexy. Read more About Related Sleep Disorders.
  • tilt table test
    A tilt table test is typically performed in individuals with significant fainting spells and/or dizziness of unknown cause. The test monitors an individual’s heart rate, blood pressure, and symptoms while lying flat on a table and then standing upright for a defined period of time. Diagnoses rendered after a tilt table test may include orthostatic hypotension, reflex syncope, and postural orthostatic tachycardia syndrome (POTS).
  • transcription
    Transcription is the process in which RNA is made from DNA. In transcription, the DNA sequence of a gene is transcribed (copied) to make an RNA molecule.
  • type 1 narcolepsy
    The International Classification of Sleep Disorders, third edition, divides narcolepsy into type 1 and type 2 (the previous edition used the terms narcolepsy with and without cataplexy). The new criteria for T1N require a combination of hypersomnolence and either low hypocretin levels in the cerebrospinal fluid or cataplexy plus short average sleep latency (≤ 8 minutes) and 2 or more sleep-onset REM periods (SOREMPs) on the Multiple Sleep Latency Test (MSLT). A SOREMP (within 15 minutes) of sleep onset on polysomnography (or PSG, a sleep study) may replace one of the SOREMPs on the MSLT. Read more About Related Sleep Disorders.
  • type 2 narcolepsy
    The International Classification of Sleep Disorders, third edition, divides narcolepsy into type 1 and type 2 (the previous edition used the terms narcolepsy with and without cataplexy). Type 2 narcolepsy refers to narcolepsy without cataplexy. Read more About Related Sleep Disorders.
  • v

  • vigilance
    Vigilance refers to the state of being alert and attentive.

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