394 Sleep-Wake Disorders
Risk and Prognostic Factors
Environmental. Decreased late afternoon/early evening exposure to light and/or expo-
sure to early morning light du e to early morning awakening can increase the risk of ad-
vanced sleep phase type by advancing circadian rhythms. By going to bed early, these
individuals are not exposed to light in the phase delay region of the curve, resulting in per-
petuation of advanced phase. In familial adva nced sleep phase type, a shortening of the
endogenous circadian period can result in an advanced sleep phase, although circadian pe-
riod does not appear to system atically decrease with age. 
Genetic and physiological. Advanced sleep phase type ha s demonstrated an autoso-
mal dominant mode of inheritance, including a PER2  gene mutation causing hypophos-
phorylation of the PER2 protein and a missense mutation in CKI.
Culture-Related Diagnostic Issues
African Americans may have a shorter circad ian period and larger magnitude phase ad-
vances to light than do Caucasians, possibly increasing the risk for development of ad-
vanced sleep phase type in this population.
Diagnostic Markers
A sleep diary and actigraphy may be used as diagnostic markers, as described earlier for
delayed sleep phase type. 
Functional Consequences of  Advanced Sleep Phase Type
Excessive sleepiness associated with advanced  sleep phase can have a negative effect on
cognitive performance, social interaction, and safety. Use of wake-promoting agents to
combat sleepiness or sedatives for early mo rning awakening may increase potential for
substance abuse.
Differential Diagnosis
Other sleep disorders. Behavioral factors such as irre gular sleep schedules, voluntary
early awakening, and exposure to light in th e early morning should be considered, partic-