A Takano, M Uchiyama, N Kajimura, K Mishima, Y Inoue, Y Kamei, T Kitajima, K Shibui, M Katoh, T Watanabe, Y Hashimotodani, T Nakajima, Y Ozeki, T Hori, N Yamada, R Toyoshima, N Ozaki, M Okawa, K Nagai, K Takahashi, Y Isojima, T Yamauchi, T Ebisawa
NEUROPSYCHOPHARMACOLOGY, 29(10) 1901-1909, Oct, 2004 Peer-reviewed
Recent studies have shown that functional variations in clock genes, which generate circadian rhythms through interactive positive/ negative feedback loops, contribute to the development of circadian rhythm sleep disorders in humans. Another potential candidate for rhythm disorder susceptibility is casein kinase I epsilon (CKIepsilon), which phosphorylates clock proteins and plays a pivotal role in the circadian clock. To determine whether variations in CKIe induce vulnerability to human circadian rhythm sleep disorders, such as delayed sleep phase syndrome (DSPS) and non-24-hsleep-wake syndrome (N-24), we analyzed all of the coding exons of the human CKIe gene. One of the variants identified encoded an amino-acid substitution S408N, eliminating one of the putative autophosphorylation sites in the carboxyl-terminal extension of CKIepsilon. The N408 allele was less common in both DSPS ( p = 0.028) and N-24 patients ( p = 0.035) compared to controls. When DSPS and N-24 subjects were combined, based on an a priori prediction of a common mechanism underlying both DSPS and N-24, the inverse association between the N408 allele and rhythm disorders was highly significant ( p = 0.0067, odds ratio = 0.42, 95% confidence interval: 0.22 - 0.79). In vitro kinase assay revealed that CKIe with the S408N variation was similar to1.8-fold more active than wild-type CKIepsilon. These results indicate that the N408 allele in CKIe plays a protective role in the development of DSPS and N-24 through alteration of the enzyme activity.