Herbie Murray
Non-24-hour sleep-wake disorder, formerly called free-running rhythm disorder or hypernychthemeral syndrome, is a serious, chronic circadian rhythm sleep disorder that disrupts a person's sleep-wake cycle. It is characterised by an inability to entrain to the 24-hour environment, resulting in a constant daily shift in the times when the body expects to sleep and be awake. This disorder is more common in blind people, affecting up to 70% of the totally blind, but it can also affect sighted people. Treatment options include chronotherapy, phototherapy, melatonin therapy, and the FDA-approved therapy HETLIOZ® (tasimelteon).
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What You'll Learn
- Non-24 sleep-wake disorder is a chronic circadian rhythm sleep disorder
- It is characterised by an inability to entrain to a 24-hour environment
- The condition is more common in blind people, affecting up to 70% of the totally blind
- Non-24 sleep-wake disorder can be caused by a lack of light perception
- Treatment options include phototherapy, melatonin therapy, and chronotherapy
Non-24 sleep-wake disorder is a chronic circadian rhythm sleep disorder
Non-24-hour sleep-wake disorder, also known as Non-24, N24SWD, or N24, is a chronic circadian rhythm sleep disorder. It is characterised by a desynchronisation between an individual's body clock and the external environment, resulting in a disrupted sleep-wake cycle. This disorder typically leads to difficulties in falling asleep at night and staying awake during the day.
Non-24 is one of six intrinsic circadian rhythm sleep disorders, primarily caused by internal factors. It is distinct from other sleep disorders like jet lag or shift work, which are largely influenced by external factors. The intrinsic nature of Non-24 means that the sleep-wake cycle is determined by internal mechanisms rather than external cues.
The disorder is marked by a misalignment between an individual's endogenous circadian rhythm and the natural light-dark cycle in their environment. This misalignment results in a daily shift in the circadian rhythm, affecting peak alertness times, body temperature, metabolism, and hormone secretion. The sleep-wake cycle gradually delays, causing individuals to experience sleepiness during the day and insomnia at night.
Non-24 can affect both blind and sighted individuals, although it is more prevalent among the blind population, with up to 70% of totally blind people affected. In blind individuals, the absence of light perception makes it challenging for the internal body clock to synchronise with the 24-hour day-night cycle. For sighted people, light acts as the main environmental cue to reset their body clock, but in rare cases, neurological factors or head injuries can also contribute to the development of Non-24.
The diagnosis of Non-24 typically involves the use of sleep logs, actigraphy, and wrist-worn devices like actigraphs to track sleep patterns and confirm the disorder. Treatment options include chronotherapy, phototherapy, light therapy, melatonin administration, and social support. HETLIOZ® (tasimelteon) is the first and only FDA-approved treatment for Non-24 in totally blind individuals.
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It is characterised by an inability to entrain to a 24-hour environment
Non-24-hour sleep-wake disorder (Non-24) is a chronic circadian rhythm sleep disorder characterised by an inability to entrain to a 24-hour environment. It is considered an intrinsic sleep-wake disorder because the problem is mostly due to internal factors instead of external factors, such as jet lag or shift work. It is characterised by a constant daily shift in the times when the body expects to sleep and be awake, resulting in periods of insomnia and daytime sleepiness. This is due to a person's internal body clock or circadian rhythm becoming desynchronised from the external environment.
The internal circadian clock is the body's natural timing mechanism, controlling the sleep-wake cycle. This internal clock runs a little longer than 24 hours for most people, whether sighted or blind. In sighted people, the internal clock is reset every day by environmental light cues. However, in people with Non-24, the internal clock is unable to synchronise with the 24-hour day-night cycle, resulting in a sleep-wake cycle that moves around the clock every day. This can lead to difficulties in following a regular clock scheme, with periods of daytime sleepiness and nighttime insomnia.
Non-24 is more common in blind people, affecting up to 70% of the totally blind population. Blind individuals lack the light perception necessary to synchronise their circadian clock with the 24-hour cycle. However, it is important to note that Non-24 can also affect sighted individuals, although this is less common. In sighted people, Non-24 may be associated with neurological factors, such as abnormal functioning of the suprachiasmatic nucleus (SCN) in the hypothalamus, or a malfunctioning biochemical response to light.
The cyclical nature of Non-24 is a notable feature, with individuals experiencing periods of sleeping during the day (symptomatic periods) alternating with periods of sleeping during normal nighttime hours (asymptomatic periods). This disorder can be challenging to manage, as individuals may struggle to adjust to changes in regular sleep-wake cycles, such as those caused by vacations, stress, evening activities, or time zone changes.
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The condition is more common in blind people, affecting up to 70% of the totally blind
Non-24-hour sleep-wake disorder (N24SWD or N24) is a chronic circadian rhythm sleep disorder (CRSD) in which an individual's biological clock fails to synchronize with the 24-hour day. This disorder is characterized by a daily delay in sleep and wake times, resulting in a sleep-wake cycle that gradually moves around the clock. While this disorder can affect both blind and sighted people, it is significantly more prevalent in the blind population, with up to 70% of totally blind individuals affected.
The high incidence of N24SWD in blind individuals is attributed to their lack of light input, which plays a crucial role in regulating the body's internal clock. Light acts as a "zeitgeber" or time-giver, signaling the release of the sleep hormone melatonin when it gets dark, thus triggering sleep onset. In the absence of light cues, as is the case for totally blind people, the body's master body clock runs its natural course, which is often slightly longer than 24 hours. This natural rhythm, if not entrained, can gradually drift out of alignment with the light-dark cycle in nature, resulting in N24SWD.
Several studies have confirmed the high prevalence of sleep disorders, including N24SWD, among blind individuals. One study reported that 76% of blind subjects had sleep/wake disorders, with 40% of them experiencing cyclical symptoms. Another study found that 83% of blind subjects reported at least one sleep problem, compared to 57% of sighted controls. Furthermore, up to 66% of blind individuals with a complete loss of light perception were found to have clinical criteria for N24SWD.
The condition can severely impact the social and professional lives of those affected, leading to social isolation and psychological difficulties. Diagnosis of N24SWD in blind individuals typically involves demonstrating a drifting sleep-wake cycle using sleep diaries or actigraphy, and it can be confirmed by measuring circadian biomarkers such as melatonin. Treatment options combining behavioral and drug approaches, such as melatonin supplements, have been shown to be safe and effective in managing the disorder.
While N24SWD is more commonly associated with blindness, it is important to note that it can also affect sighted individuals. In sighted people, the disorder may be linked to neurological factors, such as traumatic brain injuries, or a malfunctioning biochemical response to light, resulting in abnormal functioning of the suprachiasmatic nucleus (SCN) in the hypothalamus.
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Non-24 sleep-wake disorder can be caused by a lack of light perception
Non-24-hour sleep-wake disorder, or N24SWD, is a chronic circadian rhythm sleep disorder (CRSD) in which an individual's biological clock fails to synchronize with a 24-hour day. This disorder is characterised by a predictable circadian rhythm that exceeds 24 hours. It is distinct from irregular sleep-wake rhythm disorder (ISWRD), which is characterised by a lack of a clearly defined sleep-wake cycle.
Non-24-hour sleep-wake disorder can be caused by a lack of light perception. Light perception is crucial for maintaining a 24-hour body clock as environmental light signals the time of day to the brain. The suprachiasmatic nucleus (SCN), a cluster of neurons in the hypothalamus, acts as the body's master clock and coordinates the clocks in the pineal gland and other cells throughout the body. Light signals registered by the eyes help keep the SCN in sync with the 24-hour day-night cycle.
In individuals with a lack of light perception, such as those with total blindness, the SCN clock can drift away from a 24-hour cycle. Without light signals, there is no intrinsic way for blind individuals to realign their body clock without medical intervention. This results in a desynchronization between their biological clock and the external environment, leading to symptoms of N24SWD.
It is estimated that 55-70% of people with total blindness develop N24SWD. The onset of blindness can vary, with some individuals being born blind and others losing their vision due to illness or trauma over time. Certain conditions, such as congenital glaucoma, open-angle glaucoma, retinitis pigmentosa, or diabetic retinopathy, can lead to total blindness years or decades after their onset.
While less common, N24SWD can also affect sighted individuals with a reduced sensitivity to light. These individuals may have a malfunctioning biochemical response to light, preventing normal levels of light-activated melatonin release. Sighted people with N24SWD often have prior diagnoses of mental health disorders or head injuries, which may contribute to the development of the disorder.
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Treatment options include phototherapy, melatonin therapy, and chronotherapy
Non-24-hour sleep-wake disorder (N24SWD) is a circadian rhythm sleep disorder in which an individual's biological clock fails to synchronize with a 24-hour day. Treatment options include phototherapy, melatonin therapy, and chronotherapy.
Phototherapy, or light therapy, is widely recommended for sighted patients. It involves exposure to specific regimens of light and dark to stabilize the sleep cycle. Typically, a lightbox is used in the early morning for a duration of 2 hours. Light therapy can be effective in treating N24SWD in sighted individuals, but it is not suitable for blind people who have lost the capacity to process light.
Melatonin therapy is another treatment option for N24SWD. Melatonin is a hormone that regulates the sleep-wake cycle, and it can be taken as a supplement to help establish a regular sleep schedule. The American Academy of Sleep Medicine guidelines recommend using melatonin or melatonin receptor agonists, such as Hetlioz (tasimelteon), for the treatment of N24SWD in blind patients, except in cases of elderly patients with dementia. For sighted patients with a circadian rhythm shorter than 24 hours, melatonin may be taken in the morning along with bright light therapy at night.
Chronotherapy is a treatment approach where patients are instructed to gradually delay their bedtime and wake time by up to three hours a day until they reach a socially acceptable sleep-wake schedule. While chronotherapy can be effective in treating other sleep disorders, there is a risk that it may trigger the development of N24SWD. In some cases, patients have exchanged one circadian rhythm disorder for the more disabling N24SWD after undergoing chronotherapy.
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Frequently asked questions
Non-24 Sleep-Wake Disorder, or N24SWD, is a chronic circadian rhythm sleep disorder in which an individual's biological clock fails to synchronize with the 24-hour day-night cycle.
People with Non-24 Sleep-Wake Disorder experience a constant daily shift in their sleep-wake cycle, resulting in periods of daytime sleepiness and nighttime insomnia. They may also experience lower sleep propensity after total sleep deprivation compared to normal sleepers.
Non-24 Sleep-Wake Disorder can be caused by various factors, including genetic components, head injuries, and underlying health conditions such as mental health disorders or developmental brain disorders. It is also commonly associated with blindness, with up to 70% of totally blind individuals affected.
The diagnosis of Non-24 Sleep-Wake Disorder typically involves the use of sleep logs, actigraphy, and sleep diaries to identify a non-24-hour sleep pattern. An actigraph, a device worn on the wrist, is used to track the timing and patterns of sleep over several weeks.
The treatment for Non-24 Sleep-Wake Disorder aims to realign the individual's internal body clock with the 24-hour day-night cycle. This can include phototherapy, light therapy, melatonin therapy, timed light exposure, social interactions, feeding schedules, and activity scheduling. HETLIOZ® (tasimelteon) is the first and only FDA-approved treatment for Non-24 Sleep-Wake Disorder.
