Description

• Circadian rhythm sleep disorders (CRSDs) are a family of conditions that occur when an individual’s preferred timing of sleep is at odds with commitments to job, school, family, or social engagements. In CRSDs, intrinsic sleep is normal (i.e., there is no sleep fragmenting condition such as obstructive sleep apnea or periodic limb movement disorder). However, when forced by obligations to attempt sleep at nonpreferred times, individuals with CRSDs may complain of both sleep-initiation insomnia and excessive sleepiness in their wake time. These symptoms resolve entirely if the individual is allowed to sleep at his or her preferred time.
• Delayed sleep-wake phase disorder (DSWPD) is marked by a stable but persistent inability to initiate sleep at a desired time. Individuals are typically unable to initiate sleep until 2 to 6 hours later than societal norms (typically they initiate sleep after 2 AM), and this frequently results in insufficient sleep/sleepiness in the day that follows.

Epidemiology

DSWPD is the most common circadian rhythm disorder seen by referral in sleep medicine clinics.

Prevalence
DSWPD has an estimated prevalence of 0.1–0.2% in the general population. It is most common in adolescents, with a prevalence of 7–16%.

Etiology and Pathophysiology

In all mammals, an oscillating signal from the suprachiasmatic nucleus (SCN) in the anterior hypothalamus establishes circadian rhythms, including the propensity to be awake or asleep. The average period of this signal in humans is 24.2 hours, slightly longer than the environmental day. Certain factors, most significantly morning light, shift the timing of the circadian rhythm and thereby synchronize it to the shorter environmental cycle day by day. DSWPD occurs when the endogenous circadian rhythm is not adequately synchronized to the shorter 24-hour environmental cycle, creating a mismatch between them. Some theories to account for inadequate synchronization are that it occurs in individuals who have an abnormally long circadian period (>25 hours) or whose circadian clock does not properly respond to synchronizing agents such as light (1).

• Release of melatonin from the pineal gland in the evening initiates a cascade of events that usually triggers sleep behavior several hours later. Studies suggest that the timing of melatonin release within the circadian cycle is delayed by 40 to 120 minutes in late adolescence compared with prepuberty. This suggests that the tendency for teenagers to delay sleep onset is largely a genetically programmed developmental phenomenon.
• DSWPD is the result of biologic, behavioral, and psychosocial factors. The relative contributions of genetically predetermined endogenous factors (the shifting of the circadian phase just described) versus voluntary behaviors that delay bedtime are not fully delineated.

Genetics
Emerging evidence indicates a genetic component to DSWPD—a positive family history is reported in approximately 40% of individuals. In one familial case report, DSWPD was shown to occur in an autosomal dominant inheritance pattern. Polymorphisms in circadian rhythm genes such as hPer3 and clock among individuals with DSWPD constitute evidence of a genetic component to the disorder (2).

Risk Factors

DSWPD primarily affects adolescents and young adults—a cohort who have a biologic tendency to delay the onset of sleep yet often need to be up early for school/work responsibilities. Children with autism spectrum disorders also frequently have disturbed circadian rhythm cycles.

General Prevention

In DSWPD (and all CRSDs), careful attention to sleep hygiene is necessary to establish and maintain a desired sleep schedule. The most important behavioral practices to prevent an undesirably late fall-asleep time are:

• Maintain a regular sleep/wake schedule 7 days/week.
• Avoid daytime napping.
• Minimize caffeine and stimulants.
• Avoid stimulating activities in the late evening, such as computer, TV, and social interactions. A 30-minute “wind-down” time prior to bedtime in which homework, socializing, and electronic devices are off-limits is helpful.
• If computer screens are to be used in the evening, consider “apps” that filter out blue and green wavelengths because these frequencies are especially potent at further delaying the onset of sleep.
• Attempt to arise at a similar time on weekends as on school/work mornings—adolescents who sleep ad lib on the weekends (sometimes into the afternoon) often find that they have especially great difficulty initiating sleep on Sunday night and, thus, get the week off to a bad start.