Meta-analysis of 32 genome-wide linkage studies of schizophrenia.

A genome scan meta-analysis (GSMA) was carried out on 32 independent genome-wide linkage scan analyses that included 3255 pedigrees with 7413 genotyped cases affected with schizophrenia (SCZ) or related disorders. The primary GSMA divided the autosomes into 120 bins, rank-ordered the bins within each study according to the most positive linkage result in each bin, summed these ranks (weighted for study size) for each bin across studies and determined the empirical probability of a given summed rank (P(SR)) by simulation. Suggestive evidence for linkage was observed in two single bins, on chromosomes 5q (142-168 Mb) and 2q (103-134 Mb). Genome-wide evidence for linkage was detected on chromosome 2q (119-152 Mb) when bin boundaries were shifted to the middle of the previous bins. The primary analysis met empirical criteria for 'aggregate' genome-wide significance, indicating that some or all of 10 bins are likely to contain loci linked to SCZ, including regions of chromosomes 1, 2q, 3q, 4q, 5q, 8p and 10q. In a secondary analysis of 22 studies of European-ancestry samples, suggestive evidence for linkage was observed on chromosome 8p (16-33 Mb). Although the newer genome-wide association methodology has greater power to detect weak associations to single common DNA sequence variants, linkage analysis can detect diverse genetic effects that segregate in families, including multiple rare variants within one locus or several weakly associated loci in the same region. Therefore, the regions supported by this meta-analysis deserve close attention in future studies.

Genomewide linkage scan of schizophrenia in a large multicenter pedigree sample using single nucleotide polymorphisms.

A genomewide linkage scan was carried out in eight clinical samples of informative schizophrenia families. After all quality control checks, the analysis of 707 European-ancestry families included 1615 affected and 1602 unaffected genotyped individuals, and the analysis of all 807 families included 1900 affected and 1839 unaffected individuals. Multipoint linkage analysis with correction for marker-marker linkage disequilibrium was carried out with 5861 single nucleotide polymorphisms (SNPs; Illumina version 4.0 linkage map). Suggestive evidence for linkage (European families) was observed on chromosomes 8p21, 8q24.1, 9q34 and 12q24.1 in nonparametric and/or parametric analyses. In a logistic regression allele-sharing analysis of linkage allowing for intersite heterogeneity, genomewide significant evidence for linkage was observed on chromosome 10p12. Significant heterogeneity was also observed on chromosome 22q11.1. Evidence for linkage across family sets and analyses was most consistent on chromosome 8p21, with a one-LOD support interval that does not include the candidate gene NRG1, suggesting that one or more other susceptibility loci might exist in the region. In this era of genomewide association and deep resequencing studies, consensus linkage regions deserve continued attention, given that linkage signals can be produced by many types of genomic variation, including any combination of multiple common or rare SNPs or copy number variants in a region.

Dense SNP association study for bipolar I disorder on chromosome 18p11 suggests two loci with excess paternal transmission.

Parent-of-origin effects have been implicated as mediators of genetic susceptibility for a number of complex disease phenotypes, including bipolar disorder. Specifically, evidence for linkage on chromosome 18 is modified when allelic parent-of-origin is accommodated in the analysis. Our goal was to characterize the susceptibility locus for bipolar I disorder on chromosome 18p11 and investigate this parent-of-origin hypothesis in an association context. This was achieved by genotyping single nucleotide polymorphisms (SNPs) at a high density (1 SNP/5 kb) along 13.6 megabases of the linkage region. To increase our ability to detect a susceptibility locus, we restricted the phenotype definition to include only bipolar I probands. We also restricted our study population to Ashkenazi Jewish individuals; this population has characteristics of a genetic isolate and may therefore facilitate detection of variants for complex disease. Three hundred and forty-four pedigrees (363 parent/child trios) where probands were affected with bipolar 1 disorder were genotyped. Transmission disequilibrium test analysis revealed no statistically significant association to SNPs or haplotypes within this region in this sample. However, when parent-of-origin of transmitted SNPs was taken into account, suggestive association was revealed for two separate loci.

Genetic heterogeneity in schizophrenia II: conditional analyses of affected schizophrenia sibling pairs provide evidence for an interaction between markers on chromosome 8p and 14q.

Information from multiple genome scans and collaborative efforts suggests that schizophrenia is a heterogeneous, complex disorder with polygenic and environmental antecedents. In a previous paper we demonstrated that stratification of families on the basis of co-segregating phenotypes (psychotic affective disorders (PAD) and schizophrenia spectrum personality disorders (SSPD) in first-degree relatives of schizophrenic probands increased linkage evidence in the chromosome 8p21 region (D8S1771) among families with co-segregating SSPD. We have now applied a method of conditional analysis of sib-pairs affected with schizophrenia, examining shared alleles identical-by-descent (IBD) at multiple loci. The method yields enhanced evidence for linkage to the chromosome 8p21 region conditioned upon increased allele sharing at a chromosome 14 region. The method produces a more refined estimate of the putative disease locus on chromosome 8p21, narrowing the region from 18 cM (95% confidence interval) in our previous genome scan, to approximately 9.6 cM. We have also shown that the affected siblings sharing two alleles IBD at the chromosome 8p21 region and one allele IBD at the chromosome 14 region differ significantly in clinical symptoms from non-sharing affected siblings. Thus the analysis of allele sharing at a putative schizophrenia susceptibility locus conditioned on allele sharing at other loci provides another important method for dealing with heterogeneity.

Genetic heterogeneity in schizophrenia: stratification of genome scan data using co-segregating related phenotypes.

Despite considerable effort to identify susceptibility loci for schizophrenia, none have been localized. Multiple genome scans and collaborative efforts have shown evidence for linkage to regions on chromosomes 1q, 5q, 6q, 8p, 13q, 10p and 22q.(1-9) Heterogeneity is likely. We previously mapped schizophrenia susceptibility loci (SSL) to chromosomes 13q32 (P = 0.00002) and 8p21-22 (P= 0.0001) using 54 multiplex pedigrees and suggested linkage heterogeneity. We have now stratified these families based on co-segregating phenotypes in non-schizophrenic first degree relatives (schizophrenia spectrum personality disorders (SSPD); psychotic affective disorders (PAD)). Genome scans were conducted for these phenotypic subgroups of families and broadened affected phenotypes were tested. The SSPD group provided its strongest genome-wide linkage support for the chromosome 8p21 region (D8S1771) using either narrow (non-parametric lod (NPL) P= 0.000002) or broadened phenotypes (NPL P = 0.0000008) and a new region of interest on 1p was identified (P = 0.006). For PAD families, the peak NPL in the genome scan occurred on chromosome 3p26-p24 (P = 0.008). The identification of multiple susceptibility loci for schizophrenia may be enhanced by stratification of families using psychiatric diagnoses of the non-schizophrenic relatives.

Lack of linkage or association between schizophrenia and the polymorphic trinucleotide repeat within the KCNN3 gene on chromosome 1q21.

To determine the importance of a candidate gene KCNN3 (formerly named hSKCa3) in the susceptibility to schizophrenia, we have studied the genotypes of a (CAG)n polymorphism within this gene in the DNAs of the members of 54 multiplex families with this disease. Parametric and nonparametric linkage analysis did not provide evidence for linkage between KCNN3 (that we mapped to chromosome 1q21) and schizophrenia. Furthermore, we observed no difference in the distribution of the (CAG)n alleles between affected and normal individuals. These results do not support the hypothesis that larger KCNN3 alleles are preferentially associated with schizophrenia [Chandy et al. 1998 Mol Psychiatr 3:32-37] in individuals from multiply affected families.

No evidence for linkage between schizophrenia and markers at chromosome 15q13-14.

Freedman et al. [1997: Proc Natl Acad Sci USA 94:587-592] reported linkage in nine multiplex schizophrenia families to markers on chromosome 15, using impaired neuronal inhibition to repeated auditory stimuli (P50), a neurophysiological deficit associated with schizophrenia, as the phenotype. The highest LOD score obtained (5.3 at theta = 0) was for marker D15S1360 mapped to chromosome 15q13-14, less than 120 kb from the alpha7-nicotinic receptor (CHRNA7) gene. The study also reported a small positive LOD score for D15S1360 when examined for linkage to the schizophrenia phenotype. Following these findings, we examined three polymorphic markers (D15S1360, L76630, and ACTC) on chromosome 15q13-14 near the CHRNA7 gene for linkage to schizophrenia, using 54 pedigrees from an independent study. Alleles for these three markers were genotyped and analyzed using parametric and nonparametric methods. No LOD score above 1.00 was obtained for any marker, and affected sib-pair analysis likewise showed no evidence for linkage. We conclude that in our families the region around the CHRNA7 locus does not contain a major locus for susceptibility to schizophrenia.

Schizophrenia susceptibility loci on chromosomes 13q32 and 8p21.

Schizophrenia is a common disorder characterized by psychotic symptoms; diagnostic criteria have been established. Family, twin and adoption studies suggest that both genetic and environmental factors influence susceptibility (heritability is approximately 71%; ref. 2), however, little is known about the aetiology of schizophrenia. Clinical and family studies suggest aetiological heterogeneity. Previously, we reported that regions on chromosomes 22, 3 and 8 may be associated with susceptibility to schizophrenia, and collaborations provided some support for regions on chromosomes 8 and 22 (refs 9-13). We present here a genome-wide scan for schizophrenia susceptibility loci (SSL) using 452 microsatellite markers on 54 multiplex pedigrees. Non-parametric linkage (NPL) analysis provided significant evidence for an SSL on chromosome 13q32 (NPL score=4.18; P=0.00002), and suggestive evidence for another SSL on chromosome 8p21-22 (NPL=3.64; P=0.0001). Parametric linkage analysis provided additional support for these SSL. Linkage evidence at chromosome 8 is weaker than that at chromosome 13, so it is more probable that chromosome 8 may be a false positive linkage. Additional putative SSL were noted on chromosomes 14q13 (NPL=2.57; P=0.005), 7q11 (NPL=2.50, P=0.007) and 22q11 (NPL=2.42, P=0.009). Verification of suggestive SSL on chromosomes 13q and 8p was attempted in a follow-up sample of 51 multiplex pedigrees. This analysis confirmed the SSL in 13q14-q33 (NPL=2.36, P=0.007) and supported the SSL in 8p22-p21 (NPL=1.95, P=0.023).

Schizophrenia susceptibility associated with interstitial deletions of chromosome 22q11.

We report the results of two studies examining the genetic overlap between schizophrenia and velocardiofacial syndrome. In study A, we characterize two interstitial deletions identified on chromosome 22q11 in a sample of schizophrenic patients. The size of the deletions was estimated to be between 1.5 and 2 megabases. In study B, we examine whether variations in deletion size are associated with the schizophrenic phenotype in velocardiofacial syndrome patients. Our results show that a region of the genome that has been previously implicated by genetic linkage analysis can harbor genetic lesions that increase the susceptibility to schizophrenia. Our findings should facilitate identification and cloning of the schizophrenia susceptibility gene(s) in this region and identification of more homogeneous subgroups of patients.

Schizophrenia: a genome scan targets chromosomes 3p and 8p as potential sites of susceptibility genes.

Using a systematically ascertained sample of 57 families, each having 2 or more members with a consensus diagnosis of schizophrenia (DSM-III-R criteria), we have carried out linkage studies of 520 loci, covering approximately 70% of the genome for susceptibility loci for schizophrenia. A two-stage strategy based on lod score thresholds from simulation studies of our sample identified regions for further exploration. In each region, a dense map of highly informative dinucleotide repeat polymorphisms (heterozygosity greater than .70) was analyzed using dominant, recessive, and "affected only" models and nonparametric sib pair identity-by-descent methods. For one region, 8p22-p21, affected sib-pair analyses gave a P value = .0001, corresponding to a lod score approximately equal to 3.00. For 8p22-p21, the maximum two-point lod score occurred using the "affected only" recessive model (ZMAX = 2.35; theta M = theta F); allowing for a constant sex difference in recombination fractions found in reference pedigrees, ZMAX = 2.78 (theta M/theta F = 3). For a second region, 3p26-p24, the maximum two-point lod score was 2.34 ("affected only" dominant model), and the affected sib-pair P value was .01. These two regions are worthy of further exploration as potential sites of susceptibility genes for schizophrenia.

Report from the Maryland Epidemiology Schizophrenia Linkage Study: no evidence for linkage between schizophrenia and a number of candidate and other genomic regions using a complex dominant model.

Our collaborative group has undertaken a linkage study of schizophrenia, using a systematic sample of patients admitted to Maryland hospitals. An initial sample of 39 families, each having two or more affecteds, was available for genotyping candidate genes, candidate regions, and highly polymorphic markers randomly distributed throughout the genome. We used a single complex dominant model (with a disease gene frequency of 0.005 and age-dependent penetrance for affected phenotype: for under 35, penetrance = .45; for 35 and older, penetrance = .85). We report here 130 markers, which met the exclusion criteria of LOD score < -2.00 at theta > 0.01 in at least 10 informative families, and no evidence for heterogeneity. We also report here markers that were tested as candidates for linkage to the schizophrenic phenotype. They were selected based on the following criteria: a) proximity to reported chromosomal rearrangements (both 5q and 11q), b) suggestions of linkage from other families (5q), or c) presence of a candidate gene (5q, 11q, 3q: Dopamine receptors 1, 2, and 3, respectively). We also tested for mutations of codon 717 in exon 17 of the amyloid precursor protein (APP) gene and were unable to detect the C to T substitution in our schizophrenic group.

Follow-up of a report of a potential linkage for schizophrenia on chromosome 22q12-q13.1: Part 2.

A collaboration involving four groups of investigators (Johns Hopkins University/Massachusetts Institute of Technology; Medical College of Virginia/The Health Research Board, Dublin; Institute of Psychiatry, London/University of Wales, Cardiff; Centre National de la Recherche Scientifique, Paris) was organized to confirm results suggestive of a schizophrenia susceptibility locus on chromosome 22 identified by the JHU/MIT group after a random search of the genome. Diagnostic, laboratory, and analytical reliability exercises were conducted among the groups to ensure uniformity of procedures. Data from genotyping of 3 dinucleotide repeat polymorphisms (at the loci D22S268, IL2RB, D22S307) for a combined replication sample of 256 families, each having 2 or more affected individuals with DNA, were analysed using a complex autosomal dominant model. This study provided no evidence for linkage or heterogeneity for the region 22q12-q13 under this model. We conclude that if this region confers susceptibility to schizophrenia, it must be in only a small proportion of families. Collaborative efforts to obtain large samples must continue to play an important role in the genetic search for clues to complex psychiatric disorders such as schizophrenia.

Sequential strategy to identify a susceptibility gene for schizophrenia: report of potential linkage on chromosome 22q12-q13.1: Part 1.

To identify genes responsible for the susceptibility for schizophrenia, and to test the hypothesis that schizophrenia is etiologically heterogeneous, we have studied 39 multiplex families from a systematic sample of schizophrenic patients. Using a complex autosomal dominant model, which considers only those with a diagnosis of schizophrenia or schizoaffective disorder as affected, a random search of the genome for detection of linkage was undertaken. Pairwise linkage analyses suggest a potential linkage (LRH = 34.7 or maximum lod score = 1.54) for one region (22q12-q13.1). Reanalyses, varying parameters in the dominant model, maximized the LRH at 660.7 (maximum lod score 2.82). This finding is of sufficient interest to warrant further investigation through collaborative studies.

Imipramine and chlordiazepoxide in depressive and anxiety disorders. I. Efficacy in depressed outpatients.

We randomly assigned 425 outpatients, independently classified as primarily depressed by two trained psychiatrists, to double-blind treatment with Imipramine hydrochloride, chlordiazepoxide hydrochloride, or placebo. Those patients who remained at least moderately depressed (following a two-week placebo washout period) were treated for an additional eight weeks. An endpoint analysis of 387 patients who completed two or more weeks of medication disclosed early therapeutic advantages of chlordiazepoxide. By week 4 of treatment, however, imipramine produced more improvement than did placebo and chlordiazepoxide. By six and eight weeks a general, marked therapeutic advantage was found for imipramine relative to placebo and to chlordiazepoxide on measures of depression, anxiety, anger-hostility, interpersonal sensitivity, and global improvement. Chlordiazepoxide-treated patients generally did significantly better on sleep difficulty but significantly worse on anger-hostility and interpersonal sensitivity than did imipramine- or placebo-treated patients.