Delayed sleep phase syndrome, susceptibility to

Delayed sleep phase syndrome (DSPD) is a circadian rhythm sleep disorder characterized by sleep-onset insomnia and difficulty in awakening at the desired time. Patients with DSPD have chronic difficulty in adjusting their sleep-onset and wake-up times to occupational, school, and social activities. Although psychosocial and environmental factors sometimes induce this kind of disorder, most patients with DSPD appear to have an abnormal circadian pacemaker and/or an abnormal entrainment system (summary by Hohjoh et al., 2003). [from OMIM]