Hypofunction of the N-methyl-D-aspartate (NMDA) receptor has been hypothesized to underlie the pathophysiology of schizophrenia, based on the observation that non-competitive antagonists of the NMDA receptor, such as phencyclidine, induce schizophrenia-like symptoms. Mice lacking the NR2A subunit of the NMDA receptor complex are known to display abnormal behaviour, similar to schizophrenic symptoms. The expression of NR2A starts at puberty, a period corresponding to the clinical onset of schizophrenia. This evidence suggests that the NR2A (GRIN2A) gene may play a role in the development of schizophrenia and disease phenotypes. In this study, we performed a genetic analysis of this gene in schizophrenia. Analysis of the GRIN2A gene detected four single nucleotide polymorphisms, and a variable (GT)(n) repeat in the promoter region of the gene. A case-control study (375 schizophrenics and 378 controls) demonstrated evidence of an association between the repeat polymorphism and the disease (P = 0.05, Mann-Whitney test), with longer alleles overly represented in patients. An in-vitro promoter assay revealed a length dependent inhibition of transcriptional activity by the (GT)(n) repeat, which was consistent with a receptor binding assay in postmortem brains. Significantly, the score of symptom severity in chronic patients correlated with repeat size (P = 0.01, Spearman's Rank test). These results illustrate a genotype-phenotype correlation in schizophrenia and suggest that the longer (GT)(n) stretch may act as a risk-conferring factor that worsens chronic outcome by reducing GRIN2A levels in the brain.

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Possible irregularities in serotonergic neurotransmission have been suggested as causes of a variety of neuropsychiatric diseases. We performed mutation and association analyses of the HTR4 gene, on 5q32, encoding the serotonin 4 receptor in mood disorders and schizophrenia. Mutation analysis was performed on the HTR4 exons and exon/intron boundaries in 48 Japanese patients with mood disorders and 48 patients with schizophrenia. Eight polymorphisms and four rare variants were identified. Of these, four polymorphisms at or in close proximity to exon d, g.83097C/T (HTR4-SVR (splice variant region) SNP1), g.83159G/A (HTR4-SVRSNP2), g.83164 (T)9-10 (HTR4-SVRSNP3), and g.83198A/G (HTR4-SVRSNP4), showed significant association with bipolar disorder with odds ratios of 1.5 to 2. These polymorphisms were in linkage disequilibrium, and only three common haplotypes were observed. One of the haplotypes showed significant association with bipolar disorder (P = 0.002). The genotypic and haplotypic associations with bipolar disorder were confirmed by transmission disequilibrium test in the NIMH Genetics Initiative Bipolar Pedigrees with ratios of transmitted to not transmitted alleles of 1.5 to 2.0 (P = 0.01). The same haplotype that showed association with bipolar disorder was suggested to be associated with schizophrenia in the case-control analysis (P = 0.003) but was not confirmed when Japanese schizophrenia families were tested. The polymorphisms associated with mood disorder were located within the region that encodes the divergent C-terminal tails of the 5-HT 4 receptor. These findings suggest that genomic variations in the HTR4 gene may confer susceptibility to mood disorder. Molecular Psychiatry (2002) 7, 954-961.

The tetrapeptide of cholecystokinin (CCK), CCK-4, is known to induce panic attacks in human subjects, while CCK-8 is reported to have a therapeutic effect on schizophrenia symptoms. Recently, we have identified a novel microsatellite polymorphism in the 5' upstream region of the CCK gene and shown a significant association between this polymorphism and panic disorder. In this study, we have investigated the CCK-B receptor (CCKBR) gene, which is the main constituent of the CCK receptor in the CNS. Recently, a dinucleotide repeat, (CT)(n), in the 5' regulatory region of the CCKBR gene was reported to be associated with panic disorder in Canadian samples. To evaluate an association of the CT repeat with panic disorder and schizophrenia, we genotyped 71 subjects with panic disorder, 154 schizophrenics and 199 controls. However, no evidence of allelic association was found between the polymorphic repeat of the CCKBR gene and either panic disorder or schizophrenia (P = 0.186 and 0.987, respectively). Together with the negative reports on association analyses using other polymorphisms of the CCKBR gene and Japanese samples, the present results exclude a major genetic contribution of the CCKBR gene to susceptibilities to panic disorder and schizophrenia in Japanese cohorts.

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