Ask the Sleep Experts

Common sleep questions answered by our team of sleep experts.

Meet the Sleep Team

Alcibiades Rodriguez, MD

Tatyana Mollayeva

Tatyana Mollayeva, MD, PhD

Dr. Ravi Gupta

Ravi Gupta, MD, PhD

Dr. Marta

Marta Azevedo Gonçalves, MD

Dr. Lyshova

Olga Lyshova, PhD

Click a category of questions to begin.

Disclaimer: The following answers are for informational purposes only and not intended as a substitute for medical diagnosis, advice or treatment. Contact your physician or a qualified health provider with questions regarding a medical condition. [Full Disclaimer]

Basic Sleep Questions

What does healthy sleep look like?

Healthy sleep is sleep which restores and energizes a person, so he or she feels wide awake, dynamic and energetic all day long. Health and disease are opposites, and therefore, when disease (disorder) of sleep does exist, sleep investigation is worded to identify and treat it. Sleep disorders are not rare, and they can cause serious problems, if left untreated.

How many hours of sleep should a person really get?

The optimal sleep duration requirement is largely determined by heredity. However, large large surveys show that the average sleep duration for adult person is about 7 to 8 hours.

Reference: Liu Y, Wheaton AG, Chapman DP, Cunningham TJ, Lu H, Croft JB. Prevalence of Healthy Sleep Duration among Adults–United States, 2014. MMWR Morb Mortal Wkly Rep. 2016 Feb 19;65(6):137-41

From the Press Release: “One of the most frequently asked questions that our sleep specialists receive is: ‘What is the perfect amount of sleep?’” said Dr. Clete Kushida, President of World Sleep Society, which hosts World Sleep Day each year. “The short answer is at least 7 hours in length, but a truly restorative sleep depends on duration as well as continuity and depth. Understanding the impact of sleep on physical and mental health is more important than ever before. Share our commitment and amplify our mission to advance sleep health worldwide.”

What is involved in a sleep study?

Sleep study is a clinical investigation of sleep disorders performed in a facility dedicated to sleep investigations. The patient is scheduled to arrive for sleep study 60-90 minutes before his/her usual bedtime. Before electrode application, the technologist offers an explanation of sleep study procedure. Usually, a sleep study is 6-8 hours, depending on the specific sleep problem. When the patient wakes in the morning, the technologist obtains the patient’s impression of the night’s sleep; this information will be linked to the sleep study results. In some patients, the presence of overwhelming daytime sleepiness requires adequate daytime assessment, which would require for a patient to remain in a facility the day following overnight sleep study.

What are healthy sleep habits?

A restorative sleep depends on duration of sleep, depth of sleep and continuity. A few guidelines for healthier sleep:

  • Allow for an adequate amount of sleep every night (sleep duration).
  • Establish a regular sleep and wake up schedules. Start by selecting a bedtime when you can fall asleep easily; keep your rising time constant; if you feel you are not getting enough sleep, try to go to bed earlier.
  • Ensure your sleep is continuous by eliminating as many sleep disturbances as you can (sleep continuity).
  • If you changed your usual sleep schedule, try to return to your regular schedule as soon as possible.

How can I get on a regular sleep schedule?

Maintain a regular sleep schedule by going to bed at the same time every night and waking up at the same time every day, seven days a week. Regularity is important for stabilizing your internal biological clock, allowing you to fall asleep and maintain uninterrupted sleep.

References: Giannotti F, Cortesi F, Sebastiani T, Ottaviano S. Circadian preference, sleep and daytime behaviour in adolescence. J Sleep Res. 2002 Sep;11(3):191-9

Mollayeva T, Mollayeva S, Shapiro CM, Cassidy JD, Colantonio A. Insomnia in workers with delayed recovery from mild traumatic brain injury. Sleep Med. 2016 Mar;19:153-61

Can you really get a sleep deficit?

Yes. Chronic sleep deficits are common and occur when a person does not obtain the needed amount of sleep on a permanent basis. There are numerous causes of it, including shift work and other environmental demands (occupational or family responsibilities such as caregiving for children or elderly, desire for social life, recreation, etc.), medical and sleep disorders (including sleep apnea, insomnia, movements disorders among others) that impair sleep architecture and increase nocturnal wakefulness, and the modern twenty-four hour lifestyle expectation. If you are getting less than seven hours of sleep each night, feel sleepy or tired during the day, fall asleep instantly, and/or do not feel rested upon awakening, you most likely live in a sleep deficit, and should seek professional advice.

I’ve heard if you have a healthy sleep cycle you do not need an alarm clock. Is that true?

This is an interesting question. One study investigated healthy sleepers’ ability to estimate the amount of time that has elapsed during sleep (time estimation ability; TEA) which would enable them to wake up at a predetermined time without referring to a watch or alarm clock. The time estimation ratio (TER, ratio of the subjective estimated time interval to actual time interval) was accurate for slow wave sleep (believed to be the most restorative stage of sleep), suggesting that it is SWS that supports accurate time estimation, irrespective of healthy sleepers ‘circadian phase’ during experiment, with no other sleep parameters influencing time estimation ability. Slow wave sleep activity changes across the lifespan, with a major increase during childhood and adolescence and decrease thereafter. Therefore, a majority of us may need an alarm clock, nonetheless.

References: Aritake-Okada S, Uchiyama M, Suzuki H, Tagaya H, Kuriyama K, Matsuura M, Takahashi K, Higuchi S, Mishima K. Time estimation during sleep relates to the amount of slow wave sleep in humans. Neurosci Res. 2009 Feb;63(2):115-21

What happens if you don’t dream while you sleep?

Dreaming is a mental activity that occurs in sleep and has been linked to physiology. Disturbed sleep physiology due to disorders of sleep or wakefulness has been shown to affect dream recall and content, supporting the arousal-retrieval model of dreaming. At the same time, one recent study highlighted the specific role of activated mesolimbic dopaminergic system in heightened dream recall, the reward-activation model of dreaming. Regardless of the theory, if you are healthy, absence of recall of dreams might suggest that your sleep is continuous, free of interruptions, and you are in an emotionally stable state during wakefulness. Most of us dream every night. It is normal not to remember our dreams.

References: Pérusse AD, De Koninck J, Pedneault-Drolet M, Ellis JG, Bastien CH. REM dream activity of insomnia sufferers: a systematic comparison with good sleepers. Sleep Med. 2016 Apr;20:147-54

De Gennaro L, Lanteri O, Piras F, Scarpelli S, Assogna F, Ferrara M, Caltagirone C, Spalletta G. Dopaminergic system and dream recall: An MRI study in Parkinson’s disease patients. Hum Brain Mapp. 2016 Mar;37(3):1136-47

Types of Sleep

What is REM sleep?

REM sleep is frequently referred to as paradoxical sleep, because EEG activity consists of desynchronized low-voltage activity similar to that of wakefulness. Muscles are paralyzed in REM sleep, and this sleep stage is frequently associated with dreaming. Neuroimaging studies have reported increased brain activity in REM sleep compared to nonREM sleep; however activation of cortices involved in logical thought processes is reduced compared to wakefulness.

What is the best type of sleep pattern for humans? (monophasic, biphasic, triphasic, etc.)

Sleep over 24 hours can be organized either in one block, named monophasic sleep, or in several (two or more sleep episodes over 24 hours), called biphasic or polyphasic sleep. Animal studies suggest great diversity in sleep patterns between species. Little is known about variation in organizational patterns of sleep in humans, but it is expected that monophasic sleep is present in a majority of healthy adults across the globe, with some cultures historically holding habits of napping during the day (i.e., biphasic pattern). Given the limited knowledge on the topic, the best type of sleep pattern is the one that ensures you get adequate sleep duration and best possible quality of sleep, achieved with either a single sleep episode (monophasic pattern) or with more than one (biphasic or polyphasic). It is important to point out that not every person can fall asleep at specified times throughout the day- research has shown that biphasic and polyphasic sleep patterns are present in 7 and 1% of the evaluated population, respectively. An ability to fall asleep during the day can be the result of a genetic predisposition, i.e., morningness or eveningness type, the latter of which is found to be more frequently associated with chronic sleep deprivation. If this is the case, than a biphasic sleep pattern can be viewed as an adaptation to get desired amount of sleep.

What is microsleep?

Microsleep refers to short lapses in responsiveness lasting between 0.5 and 15 seconds, associated with partial or full eye closure, preceding drowsiness, and lack of responsiveness to the external world. This is highly relevant to high risk occupations that require high alertness and immediate responsiveness such as in pilots, air-traffic controllers, and truck and car drivers.

References: Peiris MT, Jones RD, Davidson PR, Carroll GJ, Bones PJ. Frequent lapses of responsiveness during an extended visuomotor tracking task in non-sleep-deprived subjects. J Sleep Res. 2006 Sep;15(3):291-300

Impacts on Sleep

How can exercise impact your sleep?

Physical exercise is considered an effective, non-pharmacological approach to improve sleep. A recent systematic review and meta-analysis suggested that adolescents with higher subjective and objective physical activity are more likely to experience good sleep subjectively and objectively. Likewise, among adult patients with obstructive sleep apnea, physical exercise as the sole intervention was associated with improved sleep outcomes. The National Sleep Foundation has amended its sleep recommendations for good sleepers to encourage exercise without any caveat as to time of day as long as this is not at the expense of sleep duration.

References: Aiello KD, Caughey WG, Nelluri B, Sharma A, Mookadam F, Mookadam M. Effect of exercise training on sleep apnea: A systematic review and meta-analysis. Respir Med. 2016 Jul;116:85-92

Lang C, Kalak N, Brand S, Holsboer-Trachsler E, Pühse U, Gerber M. The relationship between physical activity and sleep from mid adolescence to early adulthood. A systematic review of methodological approaches and meta-analysis. Sleep Med Rev. 2016 Aug;28:32-45

Chennaoui M, Arnal PJ, Sauvet F, Léger D. Sleep and exercise: a reciprocal issue? Sleep Med Rev. 2015 Apr;20:59-72

How does alcohol affect sleep?

Alcohol is a sedative, which can help induce sleep, however, it will cause more fragmented sleep and awakenings during the night. In addition, alcohol can worsen Obstructive Sleep Apnea. Self-reported sleep problems are highly prevalent among alcohol users with rates of clinical insomnia ranging between 35 and 70%, depending on the setting and stage of use. Similarly, published studies utilizing polysomnography show that sleep latency is prolonged during periods of drinking, acute withdrawal (e.g., 1- 2 weeks of abstinence), and during post-acute withdrawal (e.g., up to 8 weeks). Evidence also points to disturbances in sleep architecture, with alcohol significantly reducing slow wave sleep time (believed to be most restorative sleep) and REM sleep time with chronic use.

Reference: Angarita GA, Emadi N, Hodges S, Morgan PT. Sleep abnormalities associated with alcohol, cannabis, cocaine, and opiate use: a comprehensive review. Addict Sci Clin Pract. 2016 Apr 26;11(1):9

How does caffeine affect sleep?

Caffeine is a central nervous system stimulator. It prolongs sleep latency, reduces total sleep time and sleep efficiency, and worsens perceived sleep quality. Slow-wave sleep is typically reduced, whereas wakefulness, transitional stage of sleep (N21 sleep) and arousals are increased. A recent systematic review reported on dose- and timing-response relationships between caffeine intake and sleep. It has been reported that older adults’ sleep may be more sensitive to caffeine than younger adults’. Earlier research also reported on genetic vulnerability due to variation in adenosine neurotransmission and metabolism.

References: Clark I, Landolt HP. Coffee, caffeine, and sleep: A systematic review of epidemiological studies and randomized controlled trials. Sleep Med Rev. 2017 Feb;31:70-78

Huang ZL, Zhang Z, Qu WM. Roles of adenosine and its receptors in sleep-wake regulation. Int Rev Neurobiol. 2014;119:349-71

Is it good to nap during the day?

This would depend on whether nocturnal sleep is of good quality and is sufficient in duration. Of course, if you feel sleepy during the day, the first step is to investigate your nocturnal sleep, and ensure everything is done to ensure it is adequate in terms of continuity, architecture and duration. Remember, healthy sleep is sleep which makes you fully alert throughout the day, so you will not need a nap. However, if napping is the only way for you to bear with chronic sleep deprivation arising from inability to get either an adequate amount of sleep due to societal responsibilities, or sleep quality due to various external and internal influences that bear on sleep function, then the pros for napping may outweigh the cons. A recent study which utilized polysomnography to investigate effect of a month-long, daily 1-hour nap regimen in a group of healthy older men and women reported that napping enhanced waking function without negatively affecting nighttime sleep.

Reference: Campbell SS, Stanchina MD, Schlang JR, Murphy PJ. Effects of a month-long napping regimen in older individuals. J Am Geriatr Soc. 2011 Feb;59(2):224-32


What is insomnia?

Insomnia is defined as difficulties to fall and stay asleep or early awakenings when you have the appropriate opportunity to do so.

How can I tell if I have insomnia?

You may have insomnia if you have:

  • Difficulty falling or staying asleep
  • Early awakenings
  • Inability to get a minimum of 7 hours of sleep every night
  • Symptoms of fatigue, sleepiness and/or difficulties with attention and concentration the next day

What are symptoms of insomnia?

Fatigue, sleepiness, difficulties with attention, concentration and memory difficulties.

What causes insomnia?

Insomnia usually runs in families and there is a strong genetic component. However, certain medications and health conditions can predispose it. Approximately 50% of patients with insomnia have a mood disorder such as depression and/or anxiety.

How does age affect insomnia?

As we get older, the slow wave sleep or deep sleep decreases, which means sleep gets lighter. Therefore, insomnia may worsen with age. It also can start in 10-15% of postmenopausal women.

How common is insomnia?

Up to 30% of people may have intermittent or some episodes of insomnia. Chronic insomnia may affect 10-15% of persons.

Do sleeping pills help insomnia?

Sleeping pills do have a role insomnia, however, these are not the only treatment. The treatment of insomnia should include Cognitive Behavioral Therapy (CBT) alone or in conjunction with sleeping pills.

How is insomnia treated?

Insomnia treatment such as Cognitive Behavioral Therapy (CBT) alone or in conjunction with sleeping pills if insomnia is the main cause. There are secondary causes such as medications, a medical disorder or a sleep disorder (for example, Restless Legs Syndrome) that may need other treatments. For primary insomnia, Cognitive Behavioral Therapy (CBT) must be part of the treatment with or without medications and a good sleep hygiene. If the patient has a psychiatric disorder, it must be addressed concomitantly.

Is insomnia genetic?

Yes, there is a strong genetic predisposition. Insomnia runs in families.

Who is at risk for insomnia?

The elderly, women, patients with family history or insomnia, patients with substance abuse problems and patients with a psychiatric disorder such as depression and/or anxiety.

What are common comorbidities of insomnia?

Mood disorders are the main comorbidity of insomnia — especially depression and anxiety disorders. Also, substance abuse disorders.

How long does insomnia last?

As a general rule, the longer the insomnia goes untreated, the more difficult it will be to control. Chronic insomnia is defined as insomnia lasting more than 3 months. The first evaluation by a sleep physician should rule out secondary causes of insomnia such as medications.

Do I have to do a sleep study to diagnose insomnia?

Most of the time, a sleep study is not needed. However, a case of Chronic insomnia, which is difficult to control, requires a sleep study to be sure we do not miss another sleep disorder, for example, Periodic Limb Movements of Sleep (PLMS).

How serious is insomnia?

If you do not sleep enough, you will have problems with fatigue, attention, concentration memory. New studies have shown link between lack of sleep and systemic hypertension and diabetes. In addition, insufficient sleep can make other conditions such as migraine headaches worse.

Sleep Apnea

What’s the difference between obstructive sleep apnea (OSA) and other categories of sleep apnea?

Obstructive sleep apnea is a common breathing disorder characterized by repetitive narrowing and closure of the upper airway during sleep. Patients typically present with loud habitual snoring, witnessed apneas and excessive daytime sleepiness.

How common is sleep apnea?

The prevalence of sleep apnea in the adult population aged 30 to 70 years is approximately 26% to 34% in men and 17% to 28% in women. Racial and ethnic factors play a significant role in specific population groups. It is known about the high prevalence of sleep apnea among Asians, among Latin American population of the USA, and also in Spain, especially among women.

How can you tell if you have sleep apnea?

The typical patient with sleep apnea is characterized by complaints.

Complaints during sleep:

  • snoring
  • reported apneas
  • choking
  • nocturia
  • sleep is unrefreshing
  • night sweating
  • bed-wetting

Complaints during wakefulness:

  • morning headaches
  • dry mouth upon waking up
  • excessive sleepiness
  • fatigue
  • lack of energy
  • acid reflux
  • irritability and mood changes
  • trouble concentrating during the day
  • a decline in memory
  • erectile dysfunction and/or low sex drive

If you snore does that mean you have sleep apnea?

Snoring may be present as an isolated phenomenon without sleep apnea, which is a social nuisance rather than a clinical disorder. Snoring is the result of tissues in the throat relaxing enough that they partially block the airway and vibrate, creating a sound. Depending on an individual’s anatomy and other lifestyle factors such as alcohol consumption and body weight, the sound of the vibration can be louder or softer.

Can children have sleep apnea?

It’s estimated than 1% to 4% of children suffer from sleep apnea, many of them being between 2 and 8 years old. Risk factors include enlarged tonsils and/or adenoids (lymph nodes in the throat behind the nose), obesity, small jaw or midface, larger-than-usual tongue, less muscle tone (such as in children with Down syndrome, cerebral palsy, and/or neuromuscular disorders).

Reference: International Classification of Sleep Disorders – Third Edition (ICSD-3)

What’s the prevalence of sleep apnea in women compared to men?

Sleep apnea used to be thought of as a “male” disease, but recent studies in the general population demonstrate that this condition have 50% of women aged 20-70 years. Of those aged 55-70 years, 14% had severe sleep apnea, in obese women this figure increases to 31%. In women, the detectability of sleep apnea rises in the postmenopausal period. The prevalence of sleep apnea in the adult population aged 30 to 70 years is approximately 26% to 34% in men and 17% to 28% in women.

Why is sleep apnea dangerous? How dangerous/serious is it?

Sleep apnea literally means “without breath during sleep”. Untreated sleep apnea has been linked to several chronic diseases, mood disorders and anxiety, risk for perioperative complications and more. Poor sleep effects every aspect of life, including one’s vitality and general outlook. Symptoms of excessive daytime sleepiness predispose the growth of traffic accidents, traumatism in the workplace and the development of mental illness.

What options do I have for treatment of sleep apnea?

Treatment for sleep apnea may include: lifestyle changes (low-calorie diet, avoidance of alcohol and sleeping pills, sufficient and appropriately timed sleep, general exercise and training of upper airway muscles), positional therapy, treatment of comorbidities, oral breathing devices or other devices (such as nasal dilators), positive airway pressure devices (gold standard); surgical treatment of pharyngeal anomalies, retrognathia or obesity.

How does weight affect sleep apnea?

There seems to be a relationship between obesity and sleep apnea. However, we have to point out that not every obese patient by body mass index has sleep apnea. A good test to do is to measure neck circumference. In men, if the neck circumference is 17 inches or higher, there’s a good chance of obstructive sleep apnea. In females, it’s 16 inches or higher.

What causes the airway to close during OSA?

When you are awake, your throat muscles keep your airway open so you can breathe. When your fall asleep, your muscles relax which narrows the throat. If your have OSA the breathing passage becomes partly or fully obstructed. The airway to close during OSA because of skeletal malformations, fat deposition, fluid accumulation and structural or functional changes of dilating muscles.

What is a CPAP and how does it work?

Continuous Positive Airway Pressure (CPAP) therapy is gently blow pressurized air through your airway at a constant pressure that keeps the throat from collapsing. CPAP machines are very basic and easy to use and are composed of three major parts: motor, hoses, mask.

Do I need a sleep study to confirm sleep apnea?

If you have symptoms of sleep apnea, your doctor may ask you to have a sleep study, called a polysomnogram. This may be done in a sleep disorder center or even at home.

What are some comorbidities of sleep apnea?

Association of sleep apnea and comorbidities may magnify the cardiovascular risk factors aggravating mortality. Comorbidities of sleep apnea are drug-resistant hypertension, congestive heart failure, diabetes, acute coronary syndrome, atrial fibrillation, stroke, pulmonary hypertension, sudden cardiac death, cancer and chronic respiratory disease.

Does sleeping on your back make sleep apnea worse?

Yes, body position plays an important role during sleep and can often make the difference between having a good night’s sleep or not. This is a particular problem as several studies have found that individuals who sleep on the back are more likely to snore or have increased apneas than those who sleep on the side. The physiological mechanism for this is most probably due to the effects of gravity on the upper airway.

Does the sleep apnea mouthpiece work as well as a CPAP machine?

CPAP machine is the mainstay for treatment of moderate to severe sleep apnea, whereas the use of sleep apnea mouthpiece has been proved beneficial for mild to moderate sleep apnea.

How is bradycardia related to sleep apnea? And what effect can that have on your health?

In some patients, simultaneous occurrence of episodes of apnea and episodes of bradycardia with a heart rate of less than 60 per minute can be recorded during sleep, which is caused by disturbances in gas exchange. This is a protective mechanism, but at the same time bradycardia increases the risk of hypoxic organ damage.

Is sleep apnea genetic?

Sleep apnea is not a genetic disease, but the pathophysiological mechanisms influenced by genetic factors include the morphology of the craniofacial and upper respiratory tracts, as well as differences in the distribution of fat deposits and in the management of breathing may be.

Other Sleep Disorder Questions

What causes snoring?

Snore is produced by vibration of the soft palate, other pharyngeal structures, or sometimes of the vocal cord, during sleep. Snoring is frequently associated with a narrowing of the upper airway, and is usually loudest and most frequent during slow wave sleep.

How can you stop snoring?

Anything that narrows the upper airway, increases nasal resistance or decreases upper airway muscle tone worsens snoring. Simple snoring can be eliminated by avoiding sleep in supine position, eradicating nasal congestion and avoiding alcohol and hypnotics. Sometimes, surgical interventions are performed if snoring is severe enough. However, snoring can also be a sign of a serious disorder, sleep apnea, which requires evaluation and treatment.

Can people sleep too much? What are the side effects of sleeping too much?

Large research studies have shown that sleep duration is widely distributed: some people sleep five hours, while others need twice that. These studies point to a genetic determination of sleep duration. Interestingly, many recent systematic reviews reported on a “ U-shape “ association between sleep duration (both short and long sleep, 7-8 hours regarded as optimal) and important outcomes, including risk of falls, stroke events and stroke mortality and mortality overall. Some have questioned the relationship between sleep duration and mortality, pointing to the fact that most studies have employed survey measures of sleep duration, which are not highly correlated with estimates based on physiologic measures.

References: Wu L, Sun D. Sleep duration and falls: a systemic review and meta-analysis of observational studies. J Sleep Res. 2017 Feb 21. doi: 10.1111/jsr.12505

Li W, Wang D, Cao S, Yin X, Gong Y, Gan Y, Zhou Y, Lu Z. Sleep duration and risk of stroke events and stroke mortality: A systematic review and meta-analysis of prospective cohort studies. Int J Cardiol. 2016 Nov 15;223:870-876

Kurina LM, McClintock MK, Chen JH, Waite LJ, Thisted RA, Lauderdale DS. Sleep duration and all-cause mortality: a critical review of measurement and associations. Ann Epidemiol. 2013 Jun;23(6):361-70

What is a shift work sleep disorder?

Shift work sleep disorder belongs to a category of circadian rhythm sleep disorders. It is characterized by recurrent complaints of insomnia and/or excessive sleepiness over the course of at least one month that is related to a work schedule that overlaps with the usual time for sleep, and which is not better explained by another medical or sleep disorder; and sleep log/actigraphy monitoring for at least one week shows sleep-time misalignment.

Reference: Handbook of Sleep Medicine, second edition 2011 Lippincott Williams &Wilkins (editors Avidan & Zee)

Is it bad for a person who works the night shift to constantly switch their sleep schedule over the weekend back to day?

While it is expected that maintaining a regular sleep schedule for the duration of the week to maintain the dynamics of circadian systems would be ideal for shift workers during days off, there is little research supporting this contention. In fact, results of the research highlight that under normal conditions, only a small minority (3%) of permanent night workers (males and females) show evidence of “complete” adjustment of their endogenous melatonin rhythm to night work, pointing to the potential value of following the natural environmental day-night schedule on days off.

References: Folkard S. Do permanent night workers show circadian adjustment? A review based on the endogenous melatonin rhythm. Chronobiol Int. 2008 Apr;25(2):215-24

Postnova S, Layden A, Robinson PA, Phillips AJ, Abeysuriya RG. Exploring sleepiness and entrainment on permanent shift schedules in a physiologically based model. J Biol Rhythms. 2012 Feb;27(1):91-102

Is narcolepsy genetic?

Narcolepsy has a genetic component, although monozygotic twin concordance (5/16 pairs) is low.

References: Segal NL. Highlights from the 15th International Congress of Twin Studies/Twin Research: Differentiating MZ Co-twins Via SNPs; Mistaken Infant Twin-Singleton Hospital Registration; Narcolepsy With Cataplexy; Hearing Loss and Language Learning/Media Mentions: Broadway Musical Recalls Conjoined Hilton Twins; High Fashion Pair; Twins Turn 102; Insights From a Conjoined Twin Survivor. Twin Res Hum Genet. 2015 Feb;18(1):108-15. doi: 10.1017/thg.2014.84.

How common is narcolepsy?

There is a low prevalence of familial cases. The risk of narcolepsy type 1 (narcolepsy-cataplexy) in first-degree relatives of affected individuals is approximately 1% to 2%, which is tenfold to forty-fold increased compared to the general population.

Reference: International Classification of Sleep Disorders – Third Edition (ICSD-3)

How common is restless leg syndrome?

The overall prevalence of RLS has been estimated at 5% to 10% in European and North American population-based studies. In Asian countries, lower prevalence was reported.

Reference: International Classification of Sleep Disorders – Third Edition (ICSD-3)

What age groups are commonly affected by RLS?

Onset of RLS symptoms occurs at all ages, from childhood to late adult life. Early-onset RLS (prior to age 45 years) is more familial and associated with slower progression than late-onset RLS.

Reference: International Classification of Sleep Disorders – Third Edition (ICSD-3)

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