H. J. Williams

Support for genetic variation in neuregulin 1 and susceptibility to schizophrenia

Recently, it has been reported that genetic variants around the gene neuregulin 1 are associated with schizophrenia in an Icelandic sample. Of particular interest was the presence of a single-risk haplotype that was significantly over-represented in schizophrenic individuals compared to controls (15.4u2009:u20097.5%, P=6.7 × 10−6). We have attempted to replicate this result in our large collection of 573 schizophrenia cases and 618 controls. We found that the risk haplotype was more common in cases than controls (9.5u2009:u20097.5%; P=0.04), and especially in our subset of 141 cases with a family history of schizophrenia (11.6%; P=0.019). Our results therefore replicate the Icelandic findings in an out-bred Northern European population, although they suggest that the risk conferred by the haplotype is small.

Universal, robust, highly quantitative SNP allele frequency measurement in DNA pools

Abstract. Detecting alleles that confer small increments in susceptibility to disease will require large-scale allelic association studies of single-nucleotide polymorphisms (SNPs) in candidate, or positional candidate, genes. However, current genotyping technologies are one to two orders of magnitude too expensive to permit the analysis of thousands of SNPs in large samples. We have developed and thoroughly validated a highly accurate protocol for SNP allele frequency estimation in DNA pools based upon the SNaPshot (Applied Biosystems) chemistry adaptation of primer extension. Using this assay, we were able to estimate the difference in allele frequencies between pooled cases and controls (Δ) with a mean error of 0.01. Moreover, when we genotyped seven different SNPs in a single multiplex reaction, the results were similar, with a mean error for Δ of 0.008. The assay performed well for alleles of low frequency alleles (f~0.05) and was accurate even with relatively poor quality DNA template extracted from mouthwashes. Our assay conditions are generalisable, universal, robust and, therefore, for the first time, permit high-throughput association analysis at a realistic cost.

Genome-wide association study of schizophrenia in a Japanese population.

BACKGROUNDnGenome-wide association studies have detected a small number of weak but strongly supported schizophrenia risk alleles. Moreover, a substantial polygenic component to the disorder consisting of a large number of such alleles has been reported by the International Schizophrenia Consortium.nnnMETHODnWe report a Japanese genome-wide association study of schizophrenia comprising 575 cases and 564 controls. We attempted to replicate 97 markers, representing a nonredundant panel of markers derived mainly from the top 150 findings, in up to three data sets totaling 1990 cases and 5389 controls. We then attempted to replicate the observation of a polygenic component to the disorder in the Japanese and to determine whether this overlaps that seen in UK populations.nnnRESULTSnSingle-locus analysis did not reveal genome-wide support for any locus in the genome-wide association study sample (best p = 6.2 × 10(-6)) or in the complete data set in which the best supported locus was SULT6B1 (rs11895771: p = 3.7 × 10(-5) in the meta-analysis). Of loci previously supported by genome-wide association studies, we obtained in the Japanese support for NOTCH4 (rs2071287: p(meta) = 5.1 × 10(-5)). Using the approach reported by the International Schizophrenia Consortium, we replicated the observation of a polygenic component to schizophrenia within the Japanese population (p = .005). Our trans Japan-UK analysis of schizophrenia also revealed a significant correlation (best p = 7.0 × 10(-5)) in the polygenic component across populations.nnnCONCLUSIONSnThese results indicate a shared polygenic risk of schizophrenia between Japanese and Caucasian samples, although we did not detect unequivocal evidence for a novel susceptibility gene for schizophrenia.

Support for RGS4 as a susceptibility gene for schizophrenia

BACKGROUNDnThe gene encoding the regulator of G-protein signaling 4 has recently been associated with susceptibility to schizophrenia. This finding is particularly interesting, because it was replicated within the same study and also because there are functional, positional, and expression data to support the regulator of G-protein signaling 4 as a schizophrenia candidate gene. Although the original report was highly suggestive, a limitation was that the study was conducted on rather small samples.nnnMETHODSnWe have examined a large case (n = 709) control (n = 710) sample for association between schizophrenia using four markers investigated in the earlier study, denoted single nucleotide polymorphisms 1, 4, 7, and 18.nnnRESULTSnWe were able to replicate the associations with single nucleotide polymorphisms 4 and 18 that had previously been reported individually and have also identified significant association with haplotypes constructed from single nucleotide polymorphisms 1 and 4.nnnCONCLUSIONSnOur data give modest support for the hypothesis that the regulator of G-protein signaling 4 is a susceptibility gene for schizophrenia.

A systematic genomewide linkage study in 353 sib pairs with schizophrenia

We undertook a genomewide linkage study in a total of 353 affected sib pairs (ASPs) with schizophrenia. Our sample consisted of 179 ASPs from the United Kingdom, 134 from Sweden, and 40 from the United States. We typed 372 microsatellite markers at approximately 10-cM intervals. Our strongest finding was a LOD score of 3.87 on chromosome 10q25.3-q26.3, with positive results being contributed by all three samples and a LOD-1 interval of 15 cM. This finding achieved genomewide significance (P<.05), on the basis of simulation studies. We also found two regions, 17p11.2-q25.1 (maximum LOD score [MLS] = 3.35) and 22q11 (MLS = 2.29), in which the evidence for linkage was highly suggestive. Linkage to all of these regions has been supported by other studies. Moreover, we found strong evidence for linkage (genomewide P<.02) to 17p11.2-q25.1 in a single pedigree with schizophrenia. In our view, the evidence is now sufficiently compelling to undertake detailed mapping studies of these three regions.

Genome screen for loci influencing age at onset and rate of decline in late onset Alzheimer's disease

We performed an affected sib‐pair (ASP) linkage analysis to test for the effects of age at onset (AAO), rate of decline (ROD), and Apolipoprotein E (APOE) genotype on linkage to late‐onset Alzheimers disease (AD) in a sample comprising 428 sib‐pairs. We observed linkage of mean AAO to chromosome 21 in the whole sample (max LODu2009=u20092.57). This came entirely from the NIMH sample (max LODu2009=u20093.62), and was strongest in pairs with high mean AAO (>80). A similar effect was observed on chromosome 2q in the NIMH sample (max LODu2009=u20092.73); this region was not typed in the IADC/UK sample. Suggestive evidence was observed in the combined sample of linkage of AAO difference to chromosome 19q (max LODu2009=u20092.33) in the vicinity of APOE and 12p (max LODu2009=u20092.22), with linkage strongest in sib‐pairs with similar AAO. Mean ROD showed suggestive evidence of linkage to chromosome 9q in the whole sample (max LODu2009=u20092.29), with the effect strongest in the NIMH sample (max LODu2009=u20093.58), and in pairs with high mean ROD. Additional suggestive evidence was also observed in the NIMH sample with AAO difference on chromosome 6p (max LODu2009=u20092.44) and 15p (max LODu2009=u20091.87), with linkage strongest in pairs with similar AAO, and in the UK sample with mean ROD on chromosome 1p (max LODu2009=u20092.73, linkage strongest in pairs with high mean ROD). We also observed suggestive evidence of increased identical by descent (IBD) in APOE ε4 homozygotes on chromosome 1 (max LODu2009=u20093.08) and chromosome 9 (max LODu2009=u20093.34). The previously reported genome‐wide linkage of AD to chromosome 10 was not influenced by any of the covariates studied.

Multicenter linkage study of schizophrenia loci on chromosome 22q.

The hypothesis of the existence of one or more schizophrenia susceptibility loci on chromosome 22q is supported by reports of genetic linkage and association, meta-analyses of linkage, and the observation of elevated risk for psychosis in people with velocardiofacial syndrome, caused by 22q11 microdeletions. We tested this hypothesis by evaluating 10 microsatellite markers spanning 22q in a multicenter sample of 779 pedigrees. We also incorporated age at onset and sex into the analysis as covariates. No significant evidence for linkage to schizophrenia or for linkage associated with earlier age at onset, gender, or heterogeneity across sites was observed. We interpret these findings to mean that the population-wide effects of putative 22q schizophrenia susceptibility loci are too weak to detect with linkage analysis even in large samples.

Detailed analysis of PRODH and PsPRODH reveals no association with schizophrenia

People with deletion of the chromosome 22q11 region associated with velo cardio‐facial syndrome (VCFS) have a remarkably high risk of developing schizophrenia. Recently, the gene proline dehydrogenase (PRODH) which maps to 22q11 and is also an excellent functional candidate gene for psychosis, has been reported to show genetic association with schizophrenia. We have screened all the exons and adjacent intronic sequences of PRODH for the presence of sequence variation in 14 DSM IV schizophrenic subjects. Similarly, we also screened all putative exons of a sequence that is similar to proline dehydrogenase (PsPRODH) and which also maps within the deleted region. A total of nine single nucleotide polymorphisms (SNPs) were identified in PRODH, eight of which were exonic, while in PsPRODH, five SNPs were identified, one of which was in a putative exon. All samples were tested for association in a pooled sample of 368 DSM IV diagnosed schizophrenic subjects and 368 matched controls. None of the variants identified in PRODH gave even modest evidence for allelic association (Pu2009<u20090.1). In PsPRODH, two variants (−3864Gu2009>u2009A and 226Gu2009>u2009A) gave P values <u20090.1. These were individually genotyped in the same subjects that had been used to construct the pools. Although a trend for association was confirmed, neither showed evidence for association at the Pu2009≤u20090.05 level. These results do not suggest that PRODH or PsPRODH contribute to the aetiology of schizophrenia, and that the putative schizophrenia susceptibility gene in 22q11 remains unknown.

Mutation screening of the Homer gene family and association analysis in schizophrenia

Homer proteins are a group of proteins that regulate group 1 metabotropic glutamate receptor function. As altered glutamate function has been implicated in many neuro psychiatric disorders, particularly schizophrenia, we have screened all three known Homer genes for sequence variation for use under the candidate gene association paradigm. We found seven SNPs, including three in exons. Of these, none was non‐synonymous. Allele frequencies of all the detected SNPs were estimated in DNA pools of 368 schizophrenics and 368 controls. Only one (Homer 1 IVS4u2009+u200918Au2009>u2009G) was associated with schizophrenia in this sample, a finding confirmed by individual genotyping (Pu2009=u20090.01). However, in our extended sample of 680 cases and 671 controls, the evidence for association diminished (Pu2009=u20090.05). Our results suggest it is unlikely that sequence variants in the Homer genes contribute to the aetiology of schizophrenia, but the variants we identified are plausible candidates for other neuropsychiatric phenotypes.

Screening the human protocadherin 8 (PCDH8) gene in schizophrenia

Abnormalities in synaptic connectivity and plasticity have been implicated in the pathophysiology of schizophrenia. Molecules involved in the development and maintenance of neural circuitry include the recently cloned protocadherins. Human protocadherin 8 (PCDH8) is homologous to ‘arcadlin’, a molecule shown to play a role in hippocampal synaptic function in the rat. The gene encoding PCDH8 maps to a region on chromosome 13 where linkage to schizophrenia has been reported. In this study, the entire expressed sequence of the PCDH8 gene and over 800u2003bp of the 5′ flanking region were screened for polymorphisms in 30 DSM‐IV schizophrenia individuals using Denaturing High Performance Liquid Chromatography (DHPLC). A total of nine single nucleotide polymorphisms were identified, including three in the first exon that are predicted to change the amino acid sequence. One polymorphism, causing the Trp7Arg change in the putative signal peptide, showed a trend towards excess of the arginine encoding allele in a case‐control sample consisting of 520 DSM‐IV schizophrenia patients and 535 matched controls from the UK (χ2u2003=u20033.72, P[1df]u2003=u20030.054). However, this polymorphism did not show preferential transmission to schizophrenic individuals in a separate sample of 203 proband–parent trios from Bulgaria. A second, rare single nucleotide variation, predicting the non‐conservative amino acid change Glu39Ala, was found in one schizophrenic individual and their affected sibling but not in a further 352 affected individuals, nor 357 controls. These results suggest that any contribution of PCDH8 polymorphisms to schizophrenia susceptibility is likely to be weak, although the existence of rare variations of stronger effect cannot be excluded.