Familial advanced sleep-phase syndrome

Familial advanced sleep-phase syndrome (FASPS), also known as familial advanced sleep-phase disorder (FASPD), is a rare inherited circadian rhythm sleep disorder in which affected individuals experience a stable and persistent shift of the sleep-wake cycle to earlier times. People with FASPS typically feel compelled to fall asleep in the early evening (between approximately 6:00–8:30 PM) and wake spontaneously in the very early morning hours (between approximately 2:00–5:00 AM). Despite the shifted timing, the quality and total duration of sleep are generally normal, and individuals feel well-rested if they follow their natural schedule. The condition primarily affects the body's central circadian clock system, which is governed by molecular feedback loops in the suprachiasmatic nucleus of the hypothalamus. FASPS is caused by mutations in genes that encode core components of the circadian clock. The best-characterized forms involve mutations in the PER2 gene (FASPS1, associated with a serine-to-glycine substitution at a key phosphorylation site) and the CSNK1D gene encoding casein kinase I delta (FASPS2). Additional loci including CRY2, PER3, and TIMELESS have also been implicated. These mutations alter the period or stability of the molecular circadian oscillator, leading to a shortened circadian period and consequently an advanced phase of sleep and other circadian-regulated functions such as body temperature rhythm and melatonin secretion. The condition is generally considered benign from a medical standpoint, as sleep architecture remains intact. However, the markedly advanced sleep schedule can cause significant social and occupational difficulties when individuals attempt to conform to conventional schedules. Treatment options are limited but may include chronotherapy, timed bright light exposure in the evening to delay the circadian phase, and strategic timing of melatonin administration. These interventions aim to shift the circadian clock to a more conventional schedule, though their effectiveness varies among individuals. No pharmacological cure currently exists, and management is primarily supportive and behavioral.

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