Familial advanced sleep-phase syndrome (FASPS): An inherited abnormal sleep pattern in which the individual is a "morning lark" and consistently goes to sleep very early and is very early to rise. The individual's blood melatonin level and the body core temperature rhythm which are preordained by our daily biologic (circadian) clock are phase-advanced by 3 to 4 hours.
Persons with FASPS have been identified ranging from 8 to 80 years of age. FASPS is inherited as a highly penetrant autosomal dominant trait, meaning males and females alike can have it and they run a 50-50 chance of passing it on to each of their children.
This familial circadian rhythm variant has provided a unique opportunity for the genetic analysis of the human circadian clock, which keeps our body activities such as sleeping and eating on a roughly 24-hour rhythm. The gene responsible for FASPS has been found near the end of 2q, the long (q) arm of chromosome 2. Most afflicted persons, but none who sleep normally, carry a single base-pair substitution in a gene called hPer2. The substitution results in a serine to glycine mutation Thus, a variant in human sleep behavior is due to a missense mutation in a clock component, hPER2, that alters the circadian period.