Frequently Asked Questions

Non-24-Hour Disorder (Non-24) is a serious, rare, chronic circadian rhythm disorder that affects 70% of people who are totally blind. Their inability to perceive light causes a severe disruption of the master body clock, causing cycles of nighttime sleeplessness, excessive daytime sleepiness, and daytime napping.

Non-24 is common in people who are totally blind, because without light perception the master body clock is unable to sync with the 24-hour day-night cycle. People who are blind and living with Non-24 reported that Non-24 can make it extremely difficult to do well in school, hold down a job, or have satisfying relationships. Unfortunately, due to the cyclical nature of the symptoms, Non-24 is sometimes not recognized, leading to a delay in diagnosis or a misdiagnosis and inappropriate treatment.

Cyclic insomnia and sleep deprivation may lead to difficulties with concentration and memory as well as an increased risk of errors and accidents. The negative impact of Non-24 is sometimes linked to depression and mood disorders.

Non-24 can also affect people who are not blind. However, these cases are rare, and the true rate of the disorder in the general population is not known.

Clinical studies estimate that 70% of people who are totally blind have Non-24. Overall, approximately 65,000 - 95,000 people in the United States have Non-24.

Non-24 can be diagnosed with the help of 1) sleep history information captured in a sleep diary, 2) an actigraph, a device usually worn on the wrist that determines sleep patterns and circadian rhythms, and/or 3) by blood or urine analysis, all of which are collected over several weeks.

The timing of human sleep is governed by the length of time since a person last slept and their master body clock.

The master body clock controls the timing of human sleep with a rhythm that is regulated by a tiny region of the brain called the suprachiasmatic nucleus (SCN). Signals from the SCN help us stay awake and counteract the effects of fatigue. These signals peak in the evening, when the drive for sleep is high, and then diminish when bedtime approaches.

The master body clock regulates biological functions in an approximate 24-hour cycle. The cycle is usually longer than 24 hours and requires regular input from the environment to help stay in sync with the 24-hour day. In most people, circadian rhythms are precisely synchronized to the 24-hour day by exposure to environmental cues such as light. Without light, an individual’s circadian rhythm may run slightly longer than 24 hours, causing a slight delay in his/her master body clock each day.

A dyssynchrony, when the cycle is out of sync between a person’s master body clock and his or her day-night schedule, may result in a Circadian Rhythm Disorder (CRD). Examples of CRDs include Shift Work Sleep Disorder, Delayed Sleep Phase Disorder, Jet Lag, and Non-24-Hour Disorder.

Non-24 is a serious, rare, chronic circadian rhythm disorder that occurs when people are unable to reset or synchronize their master body clock to the 24-hour day-night cycle. As a result, the day-night cycle of these individuals moves gradually later and later each day.

This condition occurs in both blind and sighted individuals, but primarily affects those who are totally blind and lack the light sensitivity necessary to reset the master body clock to a 24-hour day.

One of the most common symptoms is difficulty sleeping at the desired time. People with Non-24 experience daytime sleepiness that often results in daytime napping. They may also feel as if the quality of their nighttime sleep was poor.

When circadian rhythms are out of sync, the master body clock shifts and people with Non-24 have difficulty getting to sleep at night. Each night there is a shift that pushes nighttime sleep back. This continual shift makes it virtually impossible to go to sleep at night and leads to extreme sleepiness during daytime hours. This ongoing cycle leads those with Non-24 to constantly move between regular and irregular sleep times.

At this time, there are no treatments approved by the U.S. Food and Drug Administration (FDA) for Non-24. The dietary supplement melatonin and other therapies may help relieve some of the symptoms associated with Non-24, but they do not treat the cause of the disorder. New medications that may help reset the master body clock are currently being examined in clinical trials. Questions about Non-24 should be addressed with a healthcare provider.

Several clinical studies are investigating natural and synthetic substances that may work to reset the internal clock for people with circadian rhythm disorders, including Non-24. While some promising results have been obtained, more studies are needed to develop an effective and safe treatment.

Clinical trials are currently ongoing to investigate the efficacy and safety of a new experimental treatment for people with Non-24 who are totally blind.