Tomoko Toyota

Association study on the DUSP6 gene, an affective disorder candidate gene on 12q23, performed by using fluorescence resonance energy transfer-based melting curve analysis on the LightCycler.

We introduced a new genotyping method, fluorescence resonance energy transfer-based melting curve analysis on the LightCycler, for the analysis of the gene, DUSP6 (dual specificity MAP kinase phosphatase 6), in affective disorder patients. The DUSP6 gene is located on chromosome 12q22–23, which overlaps one of the reported bipolar disorder susceptibility loci. because of its role in intracellular signalling pathways, the gene may be involved in the pathogenesis of affective disorders not only on the basis of its position but also of its function. we performed association analysis using a t>G polymorphism that gives rise to a missense mutation (Leu114Val). No evidence for a significant disease-causing effect was found in Japanese unipolars (n = 132) and bipolars (n = 122), when compared with controls (n = 299). More importantly, this study demonstrates that melting curve analysis on the LightCycler is an accurate, rapid and robust method for discriminating genotypes from biallelic markers. This strategy has the potential for use in high throughput scanning for and genotyping of single nucleotide polymorphisms (SNPs).

Genetic evidence for association between NOTCH4 and schizophrenia supported by a GWAS follow-up study in a Japanese population.

Genetic evidence for association between NOTCH4 and schizophrenia supported by a GWAS follow-up study in a Japanese population

Family-based association study of schizophrenia with 444 markers and analysis of a new susceptibility locus mapped to 11q13.3

Family‐based linkage disequilibrium (LD) mapping has been suggested as a powerful and practical alternative to linkage analysis. We have performed a genome‐wide LD survey of susceptibility loci for schizophrenia in a Japanese population. We first typed 119 schizophrenic pedigrees (357 individuals) using 444 microsatellite markers, and analyzed the data using the pedigree disequilibrium test. This analysis revealed 14 markers demonstrating significant transmission distortion. To corroborate these findings, the statistical methods were changed to the extended transmission disequilibrium test (ETDT), using 80 independent complete trios (schizophrenic proband and both parents), with 68 derived from initial pedigrees and 12 newly recruited trios. ETDT supported two markers for continued association, D11S987 on 11q13.3 (Pu2009=u20090.00009) and D16S423 on 16p13.3 (Pu2009=u20090.002). We scrutinized the most significant genomic locus on 11q11‐13 by adding 26 new markers for analysis. Results of three‐marker haplotype analysis in the region showed evidence of association with schizophrenia (most significant haplotype Pu2009=u20090.0005, global Pu2009=u20090.022). Although the present study may have missed other potential genomic intervals because of the sparse mapping density, we hope that it has identified promising anchor points for further studies to identify risk‐conferring genes for schizophrenia in the Japanese population. In addition, we provide useful information on genomic LD structures in Japanese populations, which can be used for LD mapping of complex diseases.

Karyotype analysis of 161 unrelated schizophrenics: no increased rates of X chromosome mosaicism or inv(9), using ethnically matched and age-stratified controls

Chromosomal aberrations have long been studied in an effort to identify susceptibility genes in schizophrenia. The two most frequently detected abnormalities are X chromosome mosaicism in female patients and pericentric inversions of chromosome 9 [inv(9)]. Chromosome X aneuploidies are known to be age dependent but differences due to ethnicity remain undetermined. In the case of inv(9), its prevalence in the general population varies with ethnicity. To evaluate the importance of these karyotypic changes in schizophrenia, cytogenetic analysis was performed on 161 unrelated schizophrenics of Japanese origin. We observed an increase in the incidence of X chromosome mosaicism in female schizophrenics with age. However, when compared with age matched female controls (92 individuals), no significant differences between patient and control samples were detected. Moreover, this study showed that there is no significant difference in the incidence of X chromosome loss between Japanese and Caucasian populations. The four cases with inv(9) (2.5%) detected in this study, did not differ significantly from the reported incidence of between 1.7 and 2.1% seen in the general Japanese population. We also observed a small number of additional karyotypic changes, none of which were recurrent. This is the first report to examine the comparative rates of X mosaicism in female schizophrenics and age matched controls.

High-resolution copy number variation analysis of schizophrenia in Japan

Recent schizophrenia (SCZ) studies have reported an increased burden of de novo copy number variants (CNVs) and identified specific high-risk CNVs, although with variable phenotype expressivity. However, the pathogenesis of SCZ has not been fully elucidated. Using array comparative genomic hybridization, we performed a high-resolution genome-wide CNV analysis on a mainly (92%) Japanese population (1699 SCZ cases and 824 controls) and identified 7066 rare CNVs, 70.0% of which were small (<100u2009kb). Clinically significant CNVs were significantly more frequent in cases than in controls (odds ratio=3.04, P=9.3 × 10−9, 9.0% of cases). We confirmed a significant association of X-chromosome aneuploidies with SCZ and identified 11 de novo CNVs (e.g., MBD5 deletion) in cases. In patients with clinically significant CNVs, 41.7% had a history of congenital/developmental phenotypes, and the rate of treatment resistance was significantly higher (odds ratio=2.79, P=0.0036). We found more severe clinical manifestations in patients with two clinically significant CNVs. Gene set analysis replicated previous findings (e.g., synapse, calcium signaling) and identified novel biological pathways including oxidative stress response, genomic integrity, kinase and small GTPase signaling. Furthermore, involvement of multiple SCZ candidate genes and biological pathways in the pathogenesis of SCZ was suggested in established SCZ-associated CNV loci. Our study shows the high genetic heterogeneity of SCZ and its clinical features and raises the possibility that genomic instability is involved in its pathogenesis, which may be related to the increased burden of de novo CNVs and variable expressivity of CNVs.

Distribution of haplotypes derived from three common variants of the NR4A2 gene in Japanese patients with schizophrenia.

Dysregulation in dopaminergic neurotransmission might play a role in the pathogenesis of schizophrenia, and therefore genetic components of the dopamine (DA) pathway may confer risk. The NR4A2 (Nurr1) gene is essential for the development and maintenance of mesencephalic DA‐synthesizing neurons. Moreover, Nurr1 forms a heterodimer with the retinoid X receptor and disturbances in the retinoid‐signaling cascade may be involved in susceptibility to schizophrenia. To investigate the potential genetic contribution of NR4A2, we performed a case‐control association study using three common variants in the gene [−2922(C)2‐3, IVS6u2009+u200917∼+18insG, EX8u2009+u2009657(CA)9‐10] that were in strong linkage disequilibrium with each other. We did not detect a significant allelic or genotypic association. Haplotypes derived from all three polymorphisms generated similar results. These data do not support the notion that the NR4A2 gene plays a major role in risk for schizophrenia among Japanese individuals.

Two-step association analyses of the chromosome 18p11.2 region in schizophrenia detect a locus encompassing C18orf1.

Two-step association analyses of the chromosome 18p11.2 region in schizophrenia detect a locus encompassing C18orf1