question: What is the genetic basis of the Delayed Sleep-Phase Syndrome (DSPS)?
answer: Circadian gene mutations are also associated with circadian rhythm disorders such as familial advanced sleep phase syndrome, delayed sleep phase syndrome, and non-24-hour sleep-wake syndrome.  Possible association of human leucocyte antigen DR1 with delayed sleep phase syndrome. The study investigated the human leucocyte antigen (HLA), types A, B and DR, of 42 patients with delayed sleep phase syndrome (DSPS) and compared the frequencies of the antigens with those in 117 healthy controls. The comparison revealed that the gene frequencies and positivities of HLA-A, -B and -DR, except for DR1, had no significant differences between the patients and controls. The frequency of HLA-DR1 was increased in the DSPS patients as compared with that in the healthy controls (P = 0.0069 in positivity). In human leukocyte antigen (HLA) typing, the incidence of DR1 positivity alone was significantly higher in DSPS patients than in healthy subjects. 