Non-24-hour sleep-wake disorder is a disorder of the circadian rhythm that happens when the body's internal clock is not synced with earth's light and dark cycles of day and night. Affected individuals go to sleep later every night and wake up later the following day. Ultimately, the patient's schedule for sleep goes all the way around the clock. For example, an affected individual may go to sleep at nine and wake up at nine in the morning, but the next night they won't go to sleep until eleven at night. This means they wake up at eleven the next day. The delay is pushed back by a few hours each night until the individual is back to falling asleep and waking up at nine again. The circadian clock is a cluster of thousands of brain nerve cells that transmit signals throughout the body when it's time to sleep or wake up.
Various causes and risk factors are associated with this disorder. Learn about them now.
Internal Body Clock Issue
The internal clock of the human body is called the circadian clock. Non-24-hour sleep-wake disorder occurs when there is a problem with an individual's internal rhythms. When light moves from the eyes to the brain, the internal body clock activates. If the patient is not completely blind, they may have issues with the mechanism of how light moves from their eyes to their brain. The individual will not have problems with vision, but their brain is not receiving the start-up trigger that it needs to tell the body it is time to go to sleep or wake up. The circadian clock should be synchronized with the physical environment of the patient by numerous light related and non-light related stimuli. The circadian rhythms in the hypothalamus manage many biological processes including body temperature, hormone secretion, cell-cycle regulation, feeding, glucose homeostasis, and the sleep-wake cycle. When there is an alteration in the timing of these physiologic rhythms, it causes internal desynchronization. This coordination loss of rhythms can have adverse consequences on the affected individual's rest-activity cycles.
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Most individuals affected by non-24-hour sleep-wake disorder are also completely blind. This complication occurs because the body's internal clock functions according to the way light is seen. As many as three-quarters of all blind individuals suffer from effects of non-24-hour sleep-wake disorder. The human eye has two key functions. The first is to see, and the other is to absorb light. When the eye takes in light, the time of day is signaled to the brain. Individuals who are blind have no light perception regardless of the cause of their blindness. In a healthy individual, the master body clock runs twenty-four hours a day and is reset each day by light from the environment that enters the eyes. Once entering the eyes, the light hits photosensitive cells that transmit signals to the individual's brain. Because this mechanism is not activated in blind individuals, their internal body clock cycle may last less than or more than twenty-four hours. The natural cycle of non-24-hour sleep-wake disorder causes a week of severe insomnia followed by three weeks of normal sleep. Because of such cycle, blind individuals with non-24-hour sleep-wake disorder may not know they are affected.
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Autism Spectrum Disorder
Autism spectrum disorder is a range of conditions characterized by difficulties with speech, social skills, nonverbal communication, and repetitive behaviors. Autism spectrum disorder is caused by brain structure and function abnormalities that may also be influenced by genetic mutations. It is a disorder that affects the normal development of an individual's brain. When sleep and circadian centers in the brain are not properly developed because of autism spectrum disorder, non-24-hour sleep-wake disorder can occur. Not only are the circadian clocks of individuals affected by autism spectrum disorder not fully developed, but they may also have problems with melatonin production. Individuals who have non-24-hour sleep-wake disorder that is not affected by autism spectrum disorder or blindness may have development deficiencies that only affect the area of the brain that manages their sleep-wake cycle and circadian rhythms. In autism spectrum disorder patients, developmental deficiencies affect multiple parts of the brain, which can include the part where the circadian clock and sleep-wake cycle are managed.
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Some individuals who have sustained considerable trauma to the head or brain damage may develop non-24-hour sleep-wake disorder. Previous to experiencing the trauma or incurring damage, the individual was known to have a healthy and functioning sleep-wake cycle center. Not only is physical trauma to the brain a possible cause, but any tumors that form in or near the hypothalamus or pineal gland can cause non-24-hour sleep-wake disorder to develop. In some cases of such malignant or benign tumors, treatment with radiation therapy has the potential to cause damage to the sleep-wake center of the patient's brain. Another trauma that can lead to non-24-hour sleep-wake disorder is when an individual suffers damage to the brain due to an aneurysm near the suprachiasmatic nucleus or tiny region of the brain in the hypothalamus responsible for an individual's circadian rhythm. Secondary non-24-hour sleep-wake disorder can be caused by any injury, damage, or physical abnormalities that lead to a patient's total blindness.
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Insufficient Melatonin Production
Insufficient melatonin production can be the main cause or a contributing factor to an individual's development of non-24-hour sleep-wake disorder. Melatonin is a hormone produced from the amino acid tryptophan by the pineal gland in the brain. Melatonin helps link an individual's sleep to the day-night cycle. Once the circadian clock center in the brain senses it is nighttime, it stimulates the release of melatonin to make the individual feel drowsy. Even if an individual's ability to sense the time of day and relay it to the sleep-wake center in the brain is not impaired, they may still have non-24-hour sleep-wake disorder due to insufficient melatonin production. Any factor inhibiting the production and or metabolism of this hormone can result in dysfunction of an individual's circadian clock. Any patient affected by a neurodegenerative disorder may not be able to make enough melatonin, putting them at risk for developing non-24-hour sleep-wake syndrome. In addition, certain mutations in a patient's genes can cause a malfunction of the production of melatonin. In rare cases, a tumor that inhibits the proper production of melatonin can result in non-24-hour sleep-wake disorder too.