J. M. Silverman

Genome-Wide Linkage Analyses of 12 Endophenotypes for Schizophrenia From the Consortium on the Genetics of Schizophrenia

OBJECTIVE The Consortium on the Genetics of Schizophrenia has undertaken a large multisite study to characterize 12 neurophysiological and neurocognitive endophenotypic measures as a step toward understanding the complex genetic basis of schizophrenia. The authors previously demonstrated the heritability of these endophenotypes; in the present study, genetic linkage was evaluated. METHOD Each family consisted of a proband with schizophrenia, at least one unaffected sibling, and both parents. A total of 1,286 participants from 296 families were genotyped in two phases, and 1,004 individuals were also assessed for the endophenotypes. Linkage analyses of the 6,055 single-nucleotide polymorphisms that were successfully assayed, 5,760 of which were common to both phases, were conducted using both variance components and pedigree-wide regression methods. RESULTS Linkage analyses of the 12 endophenotypes collectively identified one region meeting genome-wide significance criteria, with a LOD (log of odds) score of 4.0 on chromosome 3p14 for the antisaccade task, and another region on 1p36 nearly meeting genome-wide significance, with a LOD score of 3.5 for emotion recognition. Chromosomal regions meeting genome-wide suggestive criteria with LOD scores >2.2 were identified for spatial processing (2p25 and 16q23), sensorimotor dexterity (2q24 and 2q32), prepulse inhibition (5p15), the California Verbal Learning Test (8q24), the degraded-stimulus Continuous Performance Test (10q26), face memory (10q26 and 12p12), and the Letter-Number Span (14q23). CONCLUSIONS Twelve regions meeting genome-wide significant and suggestive criteria for previously identified heritable, schizophrenia-related endophenotypes were observed, and several genes of potential neurobiological interest were identified. Replication and further genomic studies are needed to assess the biological significance of these results.

Polymorphisms in the 5'-untranslated region of the human serotonin receptor 1B (HTR1B) gene affect gene expression.

We present evidence of complex balancing regulation of HTR1B transcription by common polymorphisms in its promoter. Computational analysis of the HTR1B gene predicted that a 5′ segment, spanning common DNA sequence variations, T−261G, A−161T, and −182INS/DEL−181, contained a putative functional promoter. Using a secreted alkaline phosphatase (SEAP) reporter gene system, we found that the haplotype −261G_−182INS−181_A−161 enhanced transcriptional activity 2.3-fold compared with the haplotype T−261_−182INS−181_A−161. Conversely, −161T reversed this, and the net effect when −261G and −161T were in the same haplotype (−261G_−182INS−181_−161T) was equivalent to the major haplotype (T−261_−182INS−181_A−161). Electrophoretic mobility shift experiments showed that −261G and −161T modify the binding of transcription factors (TFs): −261G generates a new AP2 binding site, while alleles A−161 and −161T exhibit different binding characteristics to AP1. T−261G and A−161T were found to be in linkage disequilibrium (LD) with G861C in a European ancestry population. Interestingly, G861C has been reported to be associated with several psychiatric disorders. Our results indicate that HTR1B is the target of substantial transcriptional genetic regulation by common haplotypes, which are in LD with the HTR1B single-nucleotide polymorphism (SNP) most commonly used in association studies.

A transmission disequilibrium and linkage analysis of D22S278 marker alleles in 574 families: further support for a susceptibility locus for schizophrenia at 22q12

Patients with schizophrenia rarely develop rheumatoid arthritis, an autoimmune disease that exhibits genetic association with the HLA DRB1*04 gene. We previously investigated the hypothesis that schizophrenia is negatively associated with DRB1*04, and found that only half the expected number of schizophrenic patients had this gene when compared with controls. We now report the results of DRB1*04 genotyping in pedigrees multiply affected with schizophrenia. Polymerase chain reaction amplification and sequence-specific oligonucleotide probes were used to determine the DRB1 genotypes of the 187 members of 23 pedigrees multiply affected with RDC schizophrenia. DQA1, DQB1 and DPB1 genotypes were similarly determined. We analysed data using the extended transmission/disequilibrium test and found a trend for the preferential non-transmission of DRB1*04 alleles from heterozygous parents to their schizophrenic offspring (16 of 23 alleles not transmitted, chi 2 = 3.5, p = 0.06). We found no evidence for a gene of major effect using GENEHUNTER for parametric and non-parametric linkage analysis. The results from this small sample need to be interpreted with caution, but they are in keeping with previous reports and suggest that HLA DRB1*04 alleles may be associated with a reduced risk of schizophrenia.Previously, a combined analysis by the Chromosome 22 Collaborative Linkage Group (1996; Am. J. Med Genet. 67, 40-45) used an affected sib-pair analysis of a single marker (D22S278) in 574 families multiply affected by schizophrenia and found some evidence for linkage (chi 2 = 9.35, 1 df, p = 0.001), suggesting the presence of a disease locus nearby on chromosome 22q12. In order to further investigate the importance of this result, we have performed the transmission disequilibrium test (TDT) and additional parametric and non-parametric linkage analysis of the same data. The most positive result obtained was an admixture lod score of 0.9 under the assumption of locus heterogeneity and dominant transmission. The result of the TDT analysis was significant at p = 0.015 (allele-wise; chi 2 = 22, 10 df) and p = 0.00016 (genotype-wise; chi 2 = 66.2, 30 df, empirical p value = 0.0009). Overall, these results further strengthen the notion that there is a susceptibility locus for schizophrenia close to D22S278.

Group and site differences on the California Verbal Learning Test in persons with schizophrenia and their first-degree relatives: findings from the Consortium on the Genetics of Schizophrenia (COGS).

Genetic studies of schizophrenia focus increasingly on putative endophenotypes because their genetic etiology may be simpler than clinical diagnosis. The Consortium on the Genetics of Schizophrenia (COGS), a multisite family study, aims to identify the genetic basis of several endophenotypes including verbal declarative memory (VDM), a neurocognitive function that shows robust impairment in schizophrenia. We present data on one type of measure of VDM, the California Verbal Learning Test, Second Edition (CVLT-II), in schizophrenia probands (n=305), their full biological siblings (n=449) and parents (n=232), and in community comparison subjects (CCS; n=509) across seven sites. Probands performed more poorly on each of five CVLT-II measures compared to related sibling and parent groups and CCS. Siblings and parents performed significantly worse than CCS on one measure (Discriminability), but with smaller effect sizes and less impairment than observed previously. The results raise questions about the homogeneity of VDM as an endophenotype, about methodological issues related to sampling, and about psychometric issues that impact the utility of the CVLT for detecting VDM deficits in nonpsychotic relatives of persons with schizophrenia.

Gating Deficit Heritability and Correlation With Increased Clinical Severity in Schizophrenia Patients With Positive Family History

OBJECTIVE The Consortium on the Genetics of Schizophrenia Family Study evaluated 12 primary and other supplementary neurocognitive and neurophysiological endophenotypes in schizophrenia probands and their families. Previous analyses of prepulse inhibition (PPI) and P50 gating measures in this sample revealed heritability estimates that were lower than expected based on earlier family studies. Here the authors investigated whether gating measures were more heritable in multiply affected families with a positive family history compared with families with only a single affected proband (singleton). METHOD A total of 296 nuclear families consisting of a schizophrenia proband, at least one unaffected sibling, and both parents underwent a comprehensive endophenotype and clinical characterization. The Family Interview for Genetic Studies was administered to all participants and used to obtain convergent psychiatric symptom information for additional first-degree relatives. Among the families, 97 were multiply affected, and 96 were singletons. RESULTS Both PPI and P50 gating displayed substantially increased heritability in the 97 multiply affected families (47% and 36%, respectively) compared with estimates derived from the entire sample of 296 families (29% and 20%, respectively). However, no evidence for heritability was observed for either measure in the 96 singleton families. Schizophrenia probands derived from the multiply affected families also displayed a significantly increased severity of clinical symptoms compared with those from singleton families. CONCLUSIONS PPI and P50 gating measures demonstrate substantially increased heritability in schizophrenia families with a higher genetic vulnerability for illness, providing further support for the commonality of genes underlying both schizophrenia and gating measures.

A genome scan of schizophrenia

OBJECTIVE The goal of this study was to identify chromosomal regions likely to contain schizophrenia susceptibility genes. METHOD A genomewide map of 310 microsatellite DNA markers with average spacing of 11 centimorgans was genotyped in 269 individuals--126 of them with schizophrenia-related psychoses--from 43 pedigrees. Nonparametric linkage analysis was used to assess the pattern of allele sharing at each marker locus relative to the presence of disease. RESULTS Nonparametric linkage scores did not reach a genomewide level of statistical significance for any marker. There were five chromosomal regions in which empirically derived p values reached nominal levels of significance at eight marker locations. There were p values less than 0.01 at chromosomes 2q (with the peak value in this region at D2S410) and 10q (D10S1239), and there were p values less than 0.05 at chromosomes 4q (D4S2623), 9q (D9S257), and 11q (D11S2002). CONCLUSIONS The results do not support the hypothesis that a single gene causes a large increase in the risk of schizophrenia. The sample (like most others being studied for psychiatric disorders) has limited power to detect genes of small effect or those that are determinants of risk in a small proportion of families. All of the most positive results could be due to chance, or some could reflect weak linkage (genes of small effect). Multicenter studies may be useful in the effort to identify chromosomal regions most likely to contain schizophrenia susceptibility genes.