Genetic aspects of circadian dyschronism: Comparison between Asiatic-Japanese and Caucasian-French populations

Differences in period (tau) length of a variety of circadian rhythms of a given subject (internal desynchronization or circadian dyschronism) have been demonstrated in shift workers and subjects exposed to natural environmental Zeitgebers. The aims of the present study were to compare the frequency distributions of circadian tau s of the oral temperature (OT) rhythm in an Asiatic-Japanese (AJ) population to that of a Caucasian-French (CF) population, as well as to evaluate the possibility that in both populations the observed circadian dyschronism is facilitated by a similar inherited control mechanism. There were 98 healthy adult males in the CF group (including 78 shift workers) and 42 healthy subjects in the AJ group (all shift workers). OT was measured for at least 8 days, four to six times every 24 h. Power spectrum analyses were used to quantify accurately the prominent OT circadian tau. In both populations, tau s of the sleep-wake rhythm seldom differed from 24 h (four of 42 in the AJ group, none in the CF group), despite irregularities in working hours. In contrast, 30% of OT rhythm tau s differed from 24 h in both populations (exhibiting tau s of >24 h or tau s of <24 h). The tau distributions exhibited a trimodal (symmetric from both sides) distribution. The trimodal distribution in tau s of OT observed in the AJ group did not differ from that observed in the CF group. In both groups the interval of deviation from tau s of 24 h predominantly clustered in multiples of +0.8 h and -0.8 h [e.g., 24 h + n(0.8 h), yielding is of 24.8 h, 25.6 h, etc.]. The observed distribution of tau s in AJ and its multiplitive structure were nearly identical to those observed in the CF and were compatible with the Dian-Circadian model suggested for the genetic background of circadian dyschronism of CF.