Naofumi Kajimura

Association of structural polymorphisms in the human period3 gene with delayed sleep phase syndrome

Recent progress in biological clock research has facilitated genetic analysis of circadian rhythm sleep disorders, such as delayed sleep phase syndrome (DSPS) and non‐24‐h sleep–wake syndrome (N‐24). We analyzed the human period3 (hPer3) gene, one of the human homologs of the Drosophila clock‐gene period (Per), as a possible candidate for rhythm disorder susceptibility. All of the coding exons in the hPer3 gene were screened for polymorphisms by a PCR‐based strategy using genomic DNA samples from sleep disorder patients and control subjects. We identified six sequence variations with amino acid changes, of which five were common and predicted four haplotypes of the hPer3 gene. One of the haplotypes was significantly associated with DSPS (Bonferronis corrected P = 0.037; odds ratio = 7.79; 95% CI 1.59–38.3) in our study population. Our results suggest that structural polymorphisms in the hPer3 gene may be implicated in the pathogenesis of DSPS.

A Missense Variation in Human Casein Kinase I Epsilon Gene that Induces Functional Alteration and Shows an Inverse Association with Circadian Rhythm Sleep Disorders

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 (CKIɛ), which phosphorylates clock proteins and plays a pivotal role in the circadian clock. To determine whether variations in CKIɛ induce vulnerability to human circadian rhythm sleep disorders, such as delayed sleep phase syndrome (DSPS) and non-24-h sleep–wake syndrome (N-24), we analyzed all of the coding exons of the human CKIɛ 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 CKIɛ. 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 CKIɛ with the S408N variation was ∼1.8-fold more active than wild-type CKIɛ. These results indicate that the N408 allele in CKIɛ plays a protective role in the development of DSPS and N-24 through alteration of the enzyme activity.

Genetic polymorphisms of human melatonin 1b receptor gene in circadian rhythm sleep disorders and controls

Recent studies suggest that melatonin 1b (Mel1b) receptor, as well as melatonin 1a (Mel1a) receptor, is involved in the modulation of circadian rhythms in mammals. Mutational analysis was performed in the entire coding region of the human Mel1b receptor gene using genomic DNA from sleep disorder subjects. We have identified two missense mutations, G24E and L66F. However, neither is likely to be associated with sleep disorders in our study population. One of the subjects with non-24-h sleep-wake syndrome carries missense mutations in both the Mel1a and Mel1b receptor genes.

A quantitative sleep-EEG study on the effects of benzodiazepine and zopiclone in schizophrenic patients

Polysomnographic examinations (PSG) were performed on 6 male schizophrenic outpatients who were being treated with benzodiazepine (BZD) hypnotics in combination with neuroleptics and 6 healthy male volunteers. In schizophrenic subjects, zopiclone (ZPC), 15 mg/day, was substituted for the BZD hypnotics, and PSGs were recorded again during ZPC therapy. All-night sleep stage scoring was carried out by visual analysis, and computerized period-amplitude analysis of sleep EEG was also performed. The schizophrenics showed marked reduction in the amount of slow-wave sleep (SWS) and in the number of delta half-waves during all-night sleep, especially those with higher amplitude, as compared to the normals. The number of delta half-waves in the patients was markedly reduced during the first sleep cycle. The average amplitude of delta half-waves during all-night sleep in the schizophrenics was significantly lower than that in the normals. The half-wave count of total delta waves in the schizophrenics was higher during treatment with ZPC than with BZDs, although no significant differences were observed in the amount of SWS between the two treatments. Soundness of sleep in the subjective sleep assessment was better evaluated during treatment with ZPC than BZDs. These results suggest that reduction of SWS in schizophrenia may be attributable mainly to the decrease in the number of delta waves with higher amplitude and that ZPC may induce deeper sleep in schizophrenics than BZDs.