Hypernychthemeral syndrome

Hypernychthemeral Syndrome Hypernychthemeral Syndrome, also known as Non-24-Hour Sleep-Wake Disorder, is a circadian rhythm sleep disorder characterized by a chronic pattern of sleep and wake times that are not aligned with the 24-hour day. This condition is most commonly observed in individuals who are totally blind, as they lack the light perception necessary to synchronize their internal body clock with the external environment.

Symptoms

Individuals with Hypernychthemeral Syndrome experience a variety of symptoms due to the misalignment of their sleep-wake cycle with the 24-hour day. These symptoms include:

• Insomnia: Difficulty falling asleep or staying asleep during the night.
• Excessive Daytime Sleepiness: Feeling very sleepy during the day, which can affect daily functioning.
• Fatigue: Persistent tiredness and lack of energy.
• Mood Disturbances: Irritability, depression, or anxiety due to disrupted sleep patterns.

Causes

The primary cause of Hypernychthemeral Syndrome is the absence of light perception, which is crucial for the synchronization of the circadian rhythm. In individuals who are totally blind, the lack of light input to the suprachiasmatic nucleus (SCN) in the brain leads to a free-running circadian rhythm that is typically longer than 24 hours.

Diagnosis

Diagnosis of Hypernychthemeral Syndrome involves a thorough clinical evaluation, including:

• Sleep Diaries: Keeping a record of sleep and wake times over several weeks.
• Actigraphy: Using a wrist-worn device to monitor sleep-wake patterns.
• Melatonin Levels: Measuring melatonin levels to assess circadian rhythm.

Treatment

Treatment options for Hypernychthemeral Syndrome focus on aligning the sleep-wake cycle with the 24-hour day. These may include:

• Melatonin Supplements: Taking melatonin at specific times to help regulate the sleep-wake cycle.
• Light Therapy: For those with some light perception, exposure to bright light at strategic times.
• Chronotherapy: Gradually adjusting sleep times to align with the desired schedule.

Prognosis

While Hypernychthemeral Syndrome is a chronic condition, many individuals can manage their symptoms effectively with appropriate treatment. However, the disorder can significantly impact quality of life if left untreated.

See Also

• Circadian Rhythm Sleep Disorders
• Suprachiasmatic Nucleus
• Melatonin
• American Academy of Sleep Medicine. "Circadian Rhythm Sleep-Wake Disorders."
• Sack, R. L., et al. "Circadian rhythm sleep disorders: part I, basic principles, shift work and jet lag disorders."

NIH genetic and rare disease info

• NIH info on Hypernychthemeral syndrome

Hypernychthemeral syndrome is a rare disease.