Delayed sleep-phase syndrome (DSPS) 327.31, is a chronic sleep disorder in which the patient's internal body clock is not in sync with the morning-rise / evening-sleep pattern of the majority of adults. A growing body of evidence suggests that the problem is genetic. DSPS patients may have a severely reduced reaction to the re-setting effect of light on the body clock.

The disorder can lead to psychological and functional difficulties. It is often misdiagnosed and incorrectly treated due to the fact that few doctors are aware of the existence of DSPS.

Sufferers - sometimes termed "night owls" - have an identifiable sleep pattern where the majority fall asleep in the pre-dawn hours and wake in the (early) afternoon. If people with DSPS are allowed to live by their body clocks, there are generally no sleep problems. Sleepiness, melatonin-secretion, the core body temperature minimum and spontaneous awakening are all delayed by the same number of hours.

However, left unacknowledged, DSPS can cause the same problems that would be expected if persons of the same age with normal sleep patterns should force themselves to wake up in the middle of the night and try to go to sleep too early in the evening. Normal people who do not adjust well to working a night shift exhibit much the same symptoms.

For most sufferers, DSPS is evident from infancy and is a lifelong condition. For some the onset is in adolescence and for some of these it abates with maturity. Parents may find themselves chastised for not giving their children acceptable sleep patterns, and schools are generally uncooperative in helping children. This can have severe physical and mental ramifications, as children are treated for insomnia and even ADHD or ADD when there is no such problem - except for the unsocial hour at which one is able to fall asleep.

Often, sufferers manage on a few hours sleep a night during the working week, then "catch up" by sleeping excessively at the weekend and sometimes by means of afternoon or evening naps, with inevitable effects on their social lives. Using this strategy will generally become difficult or impossible after two or three decades.

Forcing a patient to go to sleep early, for example by the use of sleeping pills, and forcing early rising does not result in adaptation to the new sleeping pattern. Some sufferers report that sleeping pills are ineffective and can even exacerbate the problem. Similarly anti-depressants, which are often prescribed for insomnia, may delay sleep onset even further in DSPS.

DSPS is diagnosed by a clinical interview, actigraphic monitoring and/or a sleep log kept by the patient for at least three weeks.

Many sufferers deny the existence of any problem and refuse to accept that they may not be suited for a 9-5 lifestyle. This denial is often caused or exacerbated by friends and relatives claiming there is no such problem as DSPS and claiming the sufferer is "just lazy". 

Attempting to force oneself through 9-5 life with DSPS has been likened to "constantly living with 6 hours of jetlag".

Treatments include light therapy with a full spectrum lamp, usually 10000 lux for 30-90 minutes, and chronotherapy. These can have marked success with some patients. 

A melatonin supplement taken an hour or more before bedtime may be helpful in establishing an earlier pattern, especially in conjunction with bright light therapy at the time of spontaneous awakening. Side effects of melatonin may include disturbance of sleep, daytime sleepiness and depression. The long-term effects of melatonin administration have not been examined, production is unregulated and in some countries the treatment is not used. Some claim that large doses of vitamin B12 help normalize the onset of sleepiness, but little is known of the effectiveness of the treatment. For some patients, acupuncture may be of help.

There is no cure; treatments can only be a way to manage the condition. For many, no normalization is possible and social and work patterns must either be adjusted or the physical and mental penalties must be paid. Several studies have shown that clinical depression is frequent in DSPS patients, possibly because of patients' inability to meet social demands.

Research into DSPS, and its opposite, ASPS, is only a couple of decades old and by no means conclusive. Many doctors reject its status as "incurable", while others see it as "shifted phase", i.e. that a normal pattern exists but has been suppressed. These beliefs are highly contentious, especially among sufferers.

There has been some confusion between DSPS and Non-24 hour sleep phase syndrome, in which the circadian rhythm is extended, often to more than 27 hours. People with this syndrome will also typically sleep later than society deems normal. However, people with DSPS do, by definition, live on a 24 hour day. They can go to bed at the same time every morning and get up at the same time each day, be it 11 a.m. or 4 p.m. There have been some reports of DSPS 'developing into' non-24 hour syndrome.