[Advanced sleep phase syndrome (ASPS) and delayed sleep phase syndrome (DSPS)]

Circadian rhythm sleep disorders which may result from dysfunction of biological clock have recently been noticed and the number of patients suffering from these types of sleep disorders have been increased. In this article, clinical features, pathophysiological aspects, diagnoses and treatments for advanced sleep phase syndrome (ASPS) and delayed sleep phase syndrome (DSPS) are described. Although the pathophysiology or the etiology of ASPS and DSPS have not definitely been elucidated, the evidence that the chronobiological treatments sometimes improve patients with these disorders confirms the possibility that circadian rhythm sleep disorders are caused by dysfunction of biological clock. Further studies based on chronobiology or molecular biology are necessary to clarify the pathophysiology or the etiology of ASPS and DSPS and to develop the treatments against these circadian rhythm sleep disorders.