Coping with Non-24-Hour Sleep Wake Disorder (Non-24) by forcing one's self to keep a sleep schedule that matches the 24-hour day-night norm can lead to sleep deficits with symptoms that may mimic depression, and a possible misdiagnosis of Non-24 for a non-related psychiatric condition. Sleep deprivation itself, however, is a risk factor for depression, and can become an additional problem to manage alongside Non-24 (i.e., a co-morbidity) rather than a misdiagnosis.
As previously mentioned, Non-24 is caused by different mechanisms in blind and sighted individuals. For sighted subjects, several mechanisms for Non-24 have been suggested, including deficiencies in the ipRGC cells of the retina, under- or over-sensitivity of the eye to light, differences in the intrinsic circadian feedback loop, problems with melatonin production, etc. This is a serious disorder, extremely disruptive of people's lives, and it is not known how many people suffer from it
For totally blind patients, the disorder is caused by an inability of the circadian pacemaker to be synchronized to the 24-hour cycle by light due to the lack of a functional retina–retinohypothalamic tract–suprachiasmatic nuclei (RHT-SCN) pathway.
Non-24 can be considered intrinsic, physical, irreversible (but treatable) and not associated with any psychiatric condition in blind subjects. One previous study reported that of patients who had no psychiatric problems before the development of Non-24 symptoms, about a third developed major depression thereafter. In over a third of these depressed subjects, the symptoms of depression increased when they slept during the daytime and decreased slightly when they slept during the night. This observation suggests that the delay of sleep timing relative to the internal body clock may be an underlying cause of both Non-24 and co-morbid depression.
Correction of the delay of sleep timing may be important for the long-term treatment of both symptoms. It is very important to recognize psychiatric co-morbidities in Non-24 patients early because failure to do so may lead to unnecessary impairments in personal, academic, and family functioning at critical ages. For example, Non-24 is known to cause depression in the totally blind. When planning the initial phases of