A genomewide linkage study of age at onset in schizophrenia
ABSTRACT There is strong evidence for a genetic contribution to age at onset of schizophrenia, which probably involves both susceptibility loci for schizophrenia and modifying loci acting independent of disease risk. We sought evidence of linkage to loci that influence age at onset of schizophrenia in a sample of 94 affected sibling pairs with DSM-IV schizophrenia or schizoaffective disorder, and age at first psychiatric contact of 45 years or less. Individuals were genotyped for 229 microsatellite markers spaced at approximately 20 cM intervals throughout the genome. Loci contributing to age at onset were sought by a quantitative maximum-likelihood multipoint linkage analysis using MAPMAKER/SIBS. A nonparametric multipoint analysis was also performed. The genomewide significance of linkage results was assessed by simulation studies. There were six maximum-likelihood LOD score peaks of 1.5 or greater, the highest being on chromosome 17q (LOD = 2.54; genomewide P = 0.27). This fulfils Lander and Kruglyak's [1995: Nat Genet 11:241-247] criteria for suggestive linkage in that it would be expected to occur once or less (0.3 times) per genome scan. However, this finding should be treated with caution because the LOD score appeared to be almost solely accounted for by the pattern of ibd sharing at one marker (D17S787), with virtually no evidence of linkage over flanking markers. None of the linkage results achieved genomewide statistical significance, but the LOD score peak on chromosome 13q (LOD = 1.68) coincided with the region showing maximum evidence for linkage in the study by Blouin et al. [1998: Nat Genet 20:70-73] of categorical schizophrenia.
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ABSTRACT: It is known that RGS9-2 gene knockout mice show supersensitivity to DA and have a marked elevation in the proportion of DA D2 receptors in the high-affinity state for DA (D2(High) receptors). As this is a similar profile to that observed in the CNS from subjects with schizophrenia, we examined whether postmortem CNS tissue from subjects with the disorder and brain striata from an animal model of psychosis or schizophrenia (the amphetamine-sensitized rat) had altered levels of RGS9-2. The mRNA for RGS9-2 in 29 control hippocampi was 0.185 +/- 0.015 fg per fg of beta-glucuronidase mRNA (average +/- SE), while that in 29 schizophrenia hippocampi was 0.145 +/- 0.015 fg per fg of beta-glucuronidase mRNA (average +/- SE), a reduction of 22%. Of the many receptor-regulating genes related to G proteins, and of 11 RGS genes, RGS9-2 was the most reduced in the amphetamine-sensitized rat striatum. The reduced levels of RGS9-2 expression in both an animal model of schizophrenia and a postmortem schizophrenia brain provide further evidence implicating RGS9-2 as a candidate gene in schizophrenia.Synapse 05/2007; 61(5):303-9. DOI:10.1002/syn.20368 · 2.43 Impact Factor
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ABSTRACT: Association of the G72/G30 locus with schizophrenia and bipolar disorder has now been reported in several studies. The G72/G30 locus may be one of several that account for the evidence of linkage that spans a broad region of chromosome 13q. However, the story of G72/G30 is complex. Our meta-analysis of published association studies shows highly significant evidence of association between nucleotide variations in the G72/G30 region and schizophrenia, along with compelling evidence of association with bipolar disorder. But the associated alleles and haplotypes are not identical across studies, and some strongly associated variants are located approximately 50 kb telomeric of G72. Interestingly, G72 and G30 are transcribed in opposite directions; hence, their transcripts could cross-regulate translation. A functional native protein and functional motifs for G72 or G30 remain to be demonstrated. The interaction of G72 with d-amino acid oxidase, itself of interest as a modulator of N-methyl-d-aspartate receptors through regulation of d-serine levels, has been reported in one study and could be a key functional link that deserves further investigation. The association findings in the G72/G30 region, among the most compelling in psychiatry, may expose an important molecular pathway involved in susceptibility to schizophrenia and bipolar disorder.Biological Psychiatry 08/2006; 60(2):106-14. DOI:10.1016/j.biopsych.2006.01.019 · 9.47 Impact Factor
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ABSTRACT: Childhood-onset schizophrenia (COS), defined as onset of psychotic symptoms by age 12 years, is a rare and severe form of the disorder that seems to be clinically and neurobiologically continuous with the adult disorder. We studied a rare cohort consisting of 98 probands; 71 of these probands received a DSM-defined diagnosis of schizophrenia, and the remaining 27 were diagnosed as psychosis not otherwise specified (NOS) (upon 2-6 year follow-up, 13 have subsequently developed bipolar disorder). Two overlapping genes, G72 and G30 on 13q33.2, were identified through linkage-disequilibrium-based positional cloning. Single nucleotide polymorphisms (SNPs) at the G72/G30 locus were independently associated with both bipolar illness and schizophrenia. We analyzed SNPs at this locus with a family-based transmission disequilibrium test (TDT) and haplotype analyses for the discrete trait, as well as quantitative TDT for intermediate phenotypes, using the 88 probands (including COS and psychosis-NOS) with parental participation. We observed significant pairwise and haplotype associations between SNPs at the G72/G30 locus and psychotic illness. Furthermore, these markers showed associations with scores on a premorbid phenotype measured by the Autism Screening Questionnaire, and with age of onset. These findings, although limited by potential referral bias, confirm and strengthen previous reports that G72/G30 is a susceptibility locus both for schizophrenia and bipolar disorder.Biological Psychiatry 06/2004; 55(10):976-80. DOI:10.1016/j.biopsych.2004.01.024 · 9.47 Impact Factor