The GABA type A receptor alpha5 subunit gene is associated with bipolar I disorder.

Several genetic studies have revealed that bipolar disorders are linked with the chromosomal locus of 15q11-q13, where the gamma-aminobutyric acid (GABA) receptor alpha5 subunit gene (GABRA5) locates. GABA is one of the major neurotransmitters that may be involved in the pathogenesis of bipolar disorder. Five polymorphisms in the GABRA5 gene, -754C>T in the promoter region, IVS1-21G>A, IVS2-26T>A, (*)302C>T in 3'-UTR of exon 5, and a CA repeat polymorphism in the 3' flanking region were examined in a Japanese population. IVS1-21G>A exhibited significant differences in the distribution of the genotype and allele frequency in bipolar I disorder patients but not in bipolar II disorder patients, compared with control subjects. The haplotype analysis showed that IVS1-21G>A/IVS2-26A>T was associated with bipolar I disorder, and the IVS1-21A/IVS2-26T haplotype was a negative risk factor for susceptibility to the disorders (odds ratio: 0.57, 95% confidence interval: 0.44-0.73). These results suggest that the GABRA5 gene may confer susceptibility to bipolar I disorder.

The ZDHHC8 gene did not associate with bipolar disorder or schizophrenia.

The zinc finger and DHHC domain-containing protein 8 (ZDHHC8) gene is located on chromosome 22q11, which several genome scans have provided repeated evidence for a significant linkage with bipolar disorder (BPD) and schizophrenia. A recent study revealed that a single nucleotide polymorphism (SNP), rs175174, which has potential effects on splicing, in intron 4 of the ZDHHC8 gene is associated with susceptibility to patients with schizophrenia in US and South Africa. We examined three SNPs of the ZDHHC8 gene, including rs175174, by case-control association in Japanese patients with BPD (N=172) and controls (N=298) or patients with schizophrenia (N=407) and controls (N=497). No significant association with BPD or schizophrenia was observed. After stratification by subcategories, bipolar I and II of BPD, and paranoid and disorganized types of schizophrenia, no significant association was found, nor was a significant association with either disorder found after dividing by gender. These data suggest that the ZDHHC8 gene may not be associated with susceptibility to BPD or schizophrenia, at least in a Japanese population.

The X-box binding protein 1 (XBP1) gene is not associated with methamphetamine dependence.

Bipolar disorder has known as a high risk factor for substance abuse and dependence such as alcohol and illegal drugs. Recently, Kakiuchi et al. reported that the -116C/G polymorphism in the promoter region of the X-box binding protein 1 (XBP-1) gene, which translates a transcription factor specific for endoplasmic reticulum stress caused by misfolded proteins, was associated with bipolar disorders and schizophrenia in a Japanese population. Abuse of methamphetamine often produces affective disorders such as manic state, depressive state, and psychosis resembling paranoid-type schizophrenia. To clarify a possible involvement of XBP-1 in the etiology of methamphetamine dependence, we examined the genetic association of the -116C/G polymorphism of the XBP-1 gene by a case-control study. We found no significant association in allele and genotype frequencies of the polymorphism either with methamphetamine dependence or any clinical phenotype of dependence. Because the polymorphism is located in the promoter region of the XBP-1 gene and affects transcription activity of the gene, it is unlikely that dysfunction of XBP-1 may induces susceptibility to methamphetamine dependence.

A nonsynonymous polymorphism in the human fatty acid amide hydrolase gene did not associate with either methamphetamine dependence or schizophrenia.

Genetic contributions to the etiology of substance abuse and dependence are topics of major interest. Acute and chronic cannabis use can produce drug-induced psychosis resembling schizophrenia and worsen positive symptoms of schizophrenia. The endocannabinoid system is one of the most important neural signaling pathways implicated in substance abuse and dependence. The fatty acid amide hydrolase (FAAH) is a primary catabolic enzyme of endocannabinoids. To clarify a possible involvement of FAAH in the etiology of methamphetamine dependence/psychosis or schizophrenia, we examined the genetic association of a nonsynonymous polymorphism of the FAAH gene (Pro129Thr) by a case-control study. We found no significant association in allele and genotype frequencies of the polymorphism with either disorder. Because the Pro129Thr polymorphism reduces enzyme instability, it is unlikely that dysfunction of FAAH and enhanced endocannabinoid system induce susceptibility to either methamphetamine dependence/psychosis or schizophrenia.

The human frizzled-3 (FZD3) gene on chromosome 8p21, a receptor gene for Wnt ligands, is associated with the susceptibility to schizophrenia.

Neurodevelopmental abnormalities have been reported in studies on the pathogenesis of schizophrenia. The Wnt-signaling pathway has been implicated in a variety of processes in neurodevelopment, and the frizzled proteins have been identified as receptors for Wnt ligands. Of the frizzled proteins, frizzled-3 (FZD3) is required for formation of the neural crest and for development of major fiber tracts in the CNS. The human FZD3 gene is located on chromosome 8p21, a positive linkage locus for schizophrenia. We analyzed polymorphisms of the FZD3 gene in patients with schizophrenia and control subjects in the Japanese population. We found a significant association between schizophrenia and the FZD3 gene in single nucleotide polymorphisms and haplotype analyses. Our data suggest that dysregulation of the Wnt-signaling pathway may be involved in the susceptibility to schizophrenia.

Association study of the brain-derived neurotrophic factor (BDNF) gene with bipolar disorder.

Brain-derived neurotrophic factor (BDNF) belongs to a family of neurotrophic factors and has been demonstrated to promote the survival, differentiation, and maintenance of a broad variety of central nervous system neurons. Several reports have suggested that the BDNF gene is a plausible functional candidate gene underlying the predisposition for developing bipolar disorder (BPD). In the present study, we investigated the possible role of the BDNF gene in the etiology of BPD using a matched case-control association design in a Japanese population. There was no evidence for an allelic or genotypic association of two polymorphisms (-1360C>T and 196G>A) of the BDNF gene with BPD. Furthermore, no significant association was observed between these polymorphisms and either of two diagnostic subtypes (bipolars I and II disorder). The results suggest that the BDNF gene is unlikely to confer susceptibility to BPD.

No association between the dihydropyrimidinase-related protein 2 (DRP-2) gene and bipolar disorder in humans.

Several susceptibility loci for both of schizophrenia and bipolar disorder (BPD) have been found to overlap on several chromosomes including 8p21. Expression of dihydropyrimidinase-related protein 2 (DRP-2), which gene is located on 8p21, was found to be reduced in the brains of individuals with schizophrenia and BPD. Recently, we demonstrated a significant association between the DRP-2 gene and schizophrenia. Based on the rationale, we investigated the genetic association of the DRP-2 gene with BPD using a case-control study in the Japanese population. However, no significant associations were found between five polymorphisms of the DRP-2 gene (-975C>G, 352G>A, 426C>T, 1506T>C, and *2236T>C), and BPD, nor were associations detected between either of the polymorphisms and any subtype of BPD, bipolars I and II. The present study did not provide any evidence for a contribution of the DRP-2 gene to susceptibility to BPD.

No association between the sigma receptor type 1 gene and schizophrenia: results of analysis and meta-analysis of case-control studies.

BACKGROUND: Several lines of evidence have supported possible roles of the sigma receptors in the etiology of schizophrenia and mechanisms of antipsychotic efficacy. An association study provided genetic evidence that the sigma receptor type 1 gene (SIGMAR1) was a possible susceptibility factor for schizophrenia, however, it was not replicated by a subsequent study. It is necessary to evaluate further the possibility that the SIGMAR1 gene is associated with susceptibility to schizophrenia. METHODS: A case-control association study between two polymorphisms of the SIGMAR1 gene, G-241T/C-240T and Gln2Pro, and schizophrenia in Japanese population, and meta-analysis including present and previous studies. RESULTS: There was no significant association of any allele or genotype of the polymorphisms with schizophrenia. Neither significant association was observed with hebephrenic or paranoid subtype of schizophrenia. Furthermore, a meta-analysis including the present and previous studies comprising 779 controls and 636 schizophrenics also revealed no significant association between the SIGMAR1 gene and schizophrenia. CONCLUSION: In view of this evidence, it is likely that the SIGMAR1 gene does not confer susceptibility to schizophrenia.

A variant of the sigma receptor type-1 gene is a protective factor for Alzheimer disease.

OBJECTIVE: Some preclinical evidence suggests that the sigma receptor type 1, which plays several roles in learning and memory, may also be involved in the pathogenesis of Alzheimer disease (AD). The authors provide here genetic evidence that the sigma receptor type 1 (SIGMAR1) gene is involved in susceptibility to AD. METHODS: Two polymorphisms of the SIGMAR1 gene, G-241T/C-240T and Q2P, were analyzed in a Japanese sample of 239 patients with AD and 227 comparisons subjects. These two polymorphisms were in complete linkage disequilibrium with each other, resulting in only two haplotypes, GC-241-240Q2 and TT-241-240P2. RESULTS: There was a significant association between AD and the TT-241-240P2 haplotype of the SIGMAR1 gene and its homozygote, found with late-onset, but not early-onset AD. After stratification by epsilon4 allele status of the apolipoprotein E gene, TT-241-240P2 homozygosity of the SIGMAR1 gene reduced the risk of AD in epsilon4 allele carriers by three-fourths. CONCLUSION: The present study suggests that the TT-241-240P2 haplotype of the SIGMAR1 gene, which decreases expression of the gene, may have a protective role against susceptibility to AD.

No association between the insulin degrading enzyme gene and Alzheimer's disease in a Japanese population.

Susceptibility to Alzheimer's disease (AD) is thought to be regulated by multiple genetic factors. Recently, three independent studies have reported that loci on chromosome 10q are linked with AD, and the insulin degrading enzyme (IDE; MIM 146680) gene located on chromosome 10q23-q25; IDE is located close to the maker D10S583, which exhibits a maximum LOD score for late-onset AD. We examined seven polymorphisms in the IDE gene, the marker D10S583 in the 5' flanking region, and SNPs in introns 1, 3, 11, 20, 21, and 22 (rs#1999764, 1855915, 1970244, 538469, 551266, and 489517, respectively). Four SNPs in introns 3, 11, 20, and 22 did not exhibit any polymorphisms in the Japanese population that was studied. D10S583 and two SNPs in introns 1 and 21 did not exhibit a significant association with early- or late-onset AD. In addition, no associations were observed for subgroups of AD grouped according to APOE status. The present study indicates that the IDE gene polymorphisms do not confer susceptibility to early- or late-onset AD at least in a Japanese population.

Association of the Neprilysin gene with susceptibility to late-onset Alzheimer's disease.

Neprilysin (NEP), also known as neutral endopeptidase, enkephalinase, CD 10, and common acute lymphoblastic leukemia antigen, is a 97-kD protein. NEP can degrade amyloid beta peptides, and its mRNA and protein levels are known to be reduced in the brains of patients with Alzheimer's disease (AD), making the NEP gene a substantial candidate for an AD risk factor. We examined the genetic association of three NEP polymorphisms, a GT-repeat polymorphism and two single nucleotide polymorphisms (SNPs, -1075A>G and -1284G>C) in its promoter region, with AD in a Japanese case-control sample (240 patients and 163 controls). The GT-repeat polymorphism, but not the SNPs, was significantly associated with late-onset AD (p = 0.0007). Our findings suggest that the GT-repeat polymorphism in the promoter region of the NEP gene or some other unknown polymorphisms, which are in a linkage disequilibrium, confer a susceptibility to late-onset AD.