Delayed sleep-phase type

Delayed sleep–wake phase disorder (DSWPD) is a circadian rhythm sleep disorder experienced as a delay in the major sleep episode relative to desired or socially optimal timing (American academy of Sleep Medicine, 2014). Previously known as Delayed Sleep Phase Syndrome (DSPS) and Delayed Sleep Phase Disorder (DSPD), the disorder is especially prevalent in young people. Patients with DSWPD often have greatly delayed alignment of their circadian clock with the 24 h light–dark cycle. Sleep timing is typically delayed by 2–6 h relative to their desired timing (Micic et al., 2015). This results in chronic sleep restriction and poor sleep quality,as sleep is often attempted at times when the circadian clock is promoting wake. Beyond the direct impact on sleep, patients with DSWPD also have high rates of depressive symptoms (Alvarez et al., 1992; Murray et al., 2017; Vandeputte and de Weerd, 2003) and experience significant daytime dysfunction, including lower academic performance (Lack, 1986), increased irritability, and increased daytime sleepiness (Alvarez et al., 1992; Kripke et al., 2008).It is increasingly appreciated that the causes of DSWPD are varied and are both physiological and behavioral. In this article, we will discuss the physiological and behavioral causes of DSWPD, and point to new directions in the future study and treatment of DSWPD.