sult of maladaptive behaviors that impair sleep and increase arousal because of repeated
attempts to fall asleep at an earlier time.
Prevalence
Prevalence of delayed sleep phase type in the general population is approximately 0.17%
but appears to be greater than 7% in adolescents. Although the prevalence of familial de-
layed sleep phase type has not been established , a family history of delayed sleep phase is
present in individuals with delayed sleep phase type. 
Development and Course
Course is persistent, lasting longer than 3 mo nths, with intermittent  exacerbations through-
out adulthood. Although age at onset is variable, symptoms begin typically in adolescence
and early adulthood and persist for several mo nths to years before diagnosis is estab-
lished. Severity may decrease with ag e. Relapse of symptoms is common.
Clinical expression may vary across the lif espan depending on social, school, and work
obligations. Exacerbation is usua lly triggered by a change in work or school schedule that
requires an early rise time. Individuals wh o can alter their work schedules to accommo-
date the delayed circadian sleep and wake timing can experience remission of symptoms. 
Increased prevalence in adolescence may be a consequence of both physiological and be-
havioral factors. Hormonal changes may be involved specifically, as delayed sleep phase is as-
sociated with the onset of puberty. Thus, de layed sleep phase type in adolescents should be
differentiated from the common delay in the timi ng of circadian rhythms in this age group. In
the familial form, the course is persistent and may not improve significantly with age.