Genome-wide scan demonstrates significant linkage for male sexual orientation.

BACKGROUND: Findings from family and twin studies support a genetic contribution to the development of sexual orientation in men. However, previous studies have yielded conflicting evidence for linkage to chromosome Xq28. METHOD: We conducted a genome-wide linkage scan on 409 independent pairs of homosexual brothers (908 analyzed individuals in 384 families), by far the largest study of its kind to date. RESULTS: We identified two regions of linkage: the pericentromeric region on chromosome 8 (maximum two-point LOD = 4.08, maximum multipoint LOD = 2.59), which overlaps with the second strongest region from a previous separate linkage scan of 155 brother pairs; and Xq28 (maximum two-point LOD = 2.99, maximum multipoint LOD = 2.76), which was also implicated in prior research. CONCLUSIONS: Results, especially in the context of past studies, support the existence of genes on pericentromeric chromosome 8 and chromosome Xq28 influencing development of male sexual orientation.

Schizophrenia susceptibility alleles are enriched for alleles that affect gene expression in adult human brain.

It is widely thought that alleles that influence susceptibility to common diseases, including schizophrenia, will frequently do so through effects on gene expression. As only a small proportion of the genetic variance for schizophrenia has been attributed to specific loci, this remains an unproven hypothesis. The International Schizophrenia Consortium (ISC) recently reported a substantial polygenic contribution to that disorder, and that schizophrenia risk alleles are enriched among single-nucleotide polymorphisms (SNPs) selected for marginal evidence for association (P<0.5) from genome-wide association studies (GWAS). It follows that if schizophrenia susceptibility alleles are enriched for those that affect gene expression, those marginally associated SNPs, which are also expression quantitative trait loci (eQTLs), should carry more true association signals compared with SNPs that are not marginally associated. To test this, we identified marginally associated (P<0.5) SNPs from two of the largest available schizophrenia GWAS data sets. We assigned eQTL status to those SNPs based upon an eQTL data set derived from adult human brain. Using the polygenic score method of analysis reported by the ISC, we observed and replicated the observation that higher probability cis-eQTLs predicted schizophrenia better than those with a lower probability for being a cis-eQTL. Our data support the hypothesis that alleles conferring risk of schizophrenia are enriched among those that affect gene expression. Moreover, our data show that notwithstanding the likely developmental origin of schizophrenia, studies of adult brain tissue can, in principle, allow relevant susceptibility eQTLs to be identified.

Novel loci for major depression identified by genome-wide association study of Sequenced Treatment Alternatives to Relieve Depression and meta-analysis of three studies.

We report a genome-wide association study (GWAS) of major depressive disorder (MDD) in 1221 cases from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study and 1636 screened controls. No genome-wide evidence for association was detected. We also carried out a meta-analysis of three European-ancestry MDD GWAS data sets: STAR*D, Genetics of Recurrent Early-onset Depression and the publicly available Genetic Association Information Network-MDD data set. These data sets, totaling 3957 cases and 3428 controls, were genotyped using four different platforms (Affymetrix 6.0, 5.0 and 500 K, and Perlegen). For each of 2.4 million HapMap II single-nucleotide polymorphisms (SNPs), using genotyped data where available and imputed data otherwise, single-SNP association tests were carried out in each sample with correction for ancestry-informative principal components. The strongest evidence for association in the meta-analysis was observed for intronic SNPs in ATP6V1B2 (P=6.78 x 10⁻7), SP4 (P=7.68 x 10⁻7) and GRM7 (P=1.11 x 10⁻6). Additional exploratory analyses were carried out for a narrower phenotype (recurrent MDD with onset before age 31, N=2191 cases), and separately for males and females. Several of the best findings were supported primarily by evidence from narrow cases or from either males or females. On the basis of previous biological evidence, we consider GRM7 a strong MDD candidate gene. Larger samples will be required to determine whether any common SNPs are significantly associated with MDD.

Genome-wide association study of recurrent early-onset major depressive disorder.

A genome-wide association study was carried out in 1020 case subjects with recurrent early-onset major depressive disorder (MDD) (onset before age 31) and 1636 control subjects screened to exclude lifetime MDD. Subjects were genotyped with the Affymetrix 6.0 platform. After extensive quality control procedures, 671 424 autosomal single nucleotide polymorphisms (SNPs) and 25 068 X chromosome SNPs with minor allele frequency greater than 1% were available for analysis. An additional 1 892 186 HapMap II SNPs were analyzed based on imputed genotypic data. Single-SNP logistic regression trend tests were computed, with correction for ancestry-informative principal component scores. No genome-wide significant evidence for association was observed, assuming that nominal P<5 × 10(-8) approximates a 5% genome-wide significance threshold. The strongest evidence for association was observed on chromosome 18q22.1 (rs17077540, P=1.83 × 10(-7)) in a region that has produced some evidence for linkage to bipolar-I or -II disorder in several studies, within an mRNA detected in human brain tissue (BC053410) and approximately 75 kb upstream of DSEL. Comparing these results with those of a meta-analysis of three MDD GWAS data sets reported in a companion article, we note that among the strongest signals observed in the GenRED sample, the meta-analysis provided the greatest support (although not at a genome-wide significant level) for association of MDD to SNPs within SP4, a brain-specific transcription factor. Larger samples will be required to confirm the hypothesis of association between MDD (and particularly the recurrent early-onset subtype) and common SNPs.

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.

Analysis of 10 independent samples provides evidence for association between schizophrenia and a SNP flanking fibroblast growth factor receptor 2.

We and others have previously reported linkage to schizophrenia on chromosome 10q25-q26 but, to date, a susceptibility gene in the region has not been identified. We examined data from 3606 single-nucleotide polymorphisms (SNPs) mapping to 10q25-q26 that had been typed in a genome-wide association study (GWAS) of schizophrenia (479 UK cases/2937 controls). SNPs with P<0.01 (n=40) were genotyped in an additional 163 UK cases and those markers that remained nominally significant at P<0.01 (n=22) were genotyped in replication samples from Ireland, Germany and Bulgaria consisting of a total of 1664 cases with schizophrenia and 3541 controls. Only one SNP, rs17101921, was nominally significant after meta-analyses across the replication samples and this was genotyped in an additional six samples from the United States/Australia, Germany, China, Japan, Israel and Sweden (n=5142 cases/6561 controls). Across all replication samples, the allele at rs17101921 that was associated in the GWAS showed evidence for association independent of the original data (OR 1.17 (95% CI 1.06-1.29), P=0.0009). The SNP maps 85 kb from the nearest gene encoding fibroblast growth factor receptor 2 (FGFR2) making this a potential susceptibility gene for schizophrenia.

Transcriptome sequencing study implicates immune-related genes differentially expressed in schizophrenia: new data and a meta-analysis.

We undertook an RNA sequencing (RNAseq)-based transcriptomic profiling study on lymphoblastoid cell lines of a European ancestry sample of 529 schizophrenia cases and 660 controls, and found 1058 genes to be differentially expressed by affection status. These differentially expressed genes were enriched for involvement in immunity, especially the 697 genes with higher expression in cases. Comparing the current RNAseq transcriptomic profiling to our previous findings in an array-based study of 268 schizophrenia cases and 446 controls showed a highly significant positive correlation over all genes. Fifteen (18%) of the 84 genes with significant (false discovery rate<0.05) expression differences between cases and controls in the previous study and analyzed here again were differentially expressed by affection status here at a genome-wide significance level (Bonferroni P<0.05 adjusted for 8141 analyzed genes in total, or P<~6.1 × 10-6), all with the same direction of effect, thus providing corroborative evidence despite each sample of fully independent subjects being studied by different technological approaches. Meta-analysis of the RNAseq and array data sets (797 cases and 1106 controls) showed 169 additional genes (besides those found in the primary RNAseq-based analysis) to be differentially expressed, and provided further evidence of immune gene enrichment. In addition to strengthening our previous array-based gene expression differences in schizophrenia cases versus controls and providing transcriptomic support for some genes implicated by other approaches for schizophrenia, our study detected new genes differentially expressed in schizophrenia. We highlight RNAseq-based differential expression of various genes involved in neurodevelopment and/or neuronal function, and discuss caveats of the approach.

Does training general practitioners result in more shared decision making during consultations?

OBJECTIVE: We conducted a clustered randomised controlled trial to study the effects of shared decision making (SDM) on patient recovery. This study aims to determine whether GPs trained in SDM and reinforcing patients' treatment expectations showed more trained behaviour during their consultations than untrained GPs. METHODS: We compared 86 consultations conducted by 23 trained GPs with 89 consultations completed by 19 untrained GPs. The primary outcomes were SDM, as measured by the OPTION scale, and positive reinforcement, as measured by global observation. Secondary outcomes were the level of autonomy in decision making and the duration of the consultation. RESULTS: Intervention consultations scored significantly higher on most elements of the OPTION scale, and on the autonomy scale; however, they were three minutes longer in duration, and the mean OPTION score of the intervention group remained below average. CONCLUSION: Training GPs resulted in more SDM behaviour and more autonomy for the patient; however, this increase is not attributable to the adoption of a patient perspective. Furthermore, while we aimed to demonstrate that SDM facilitates the reinforcement of patients' positive expectations, the measurement of this behaviour was not reliable. PRACTICE IMPLICATIONS: In supporting SDM, professionals should give greater attention to patients' treatment expectations.

Closing in on genes for manic-depressive illness and schizophrenia.

Advances in the human genetic map, and in genetic analysis of linkage and association in complex inheritance traits, have led to genetic progress in the major psychoses. For chromosome 6 in schizophrenia, and chromosomes 18 and 21 in manic-depressive illness, there are reports of linkage in several independent data sets. These are small effect genes, best detected with affected-relative-pair linkage methods. Association with candidate genes is an alternative strategy to uncovering susceptibility genes for these illnesses, but convincing associations remain to be demonstrated. New clinical and laboratory investigation methods are being developed. Testing every gene in the human genome for association with illness has recently been proposed (Risch and Merikangas 1996). This would require further progress in characterizing the genome and in automated large-scale genotyping. The best type of pedigree sampling for common disease studies, whether for linkage or association, is not yet established. An endophenotype hybrid strategy can combine genetic linkage, association, and pathophysiologic studies. As clinical molecular investigation methods advance, identification of disease susceptibility mutations and delineation of their pathophysiological roles may be expected.

Linkage analysis of schizophrenia to chromosome 15.

We have mapped a sample of 68 families consisting of one or more affected sibling pairs with schizophrenia or schizoaffective disorder with 20 markers spanning all of chromosome 15 to investigate whether there is a locus on chromosome 15 that confers an increased susceptibility to schizophrenia using parametric and nonparametric linkage analyses. Allele sharing identical by descent and multipoint maximum likelihood score (MLS) statistics were employed. Results show excess allele sharing for multiple markers in 15q11.2-q25, a chromosomal region previously found linked to a decrease in the normal inhibition of the P50 auditory-evoked response to the second of paired stimuli, a decrease associated with schizophrenia. Excess allele sharing was found for markers spanning about 48 cM in 15q11.2-q25 (D15S1002-D15S1023). The greatest single point allele sharing was found at D15S659 (62.6%). The multipoint MLS scores were greater than 1.0 in the 30-52 cM interval delimited by ACTC and D15S150, with a maximum value of 2.0 with GENEHUNTER PLUS near D15S1039.

Isolation of chromosome 18-specific brain transcripts as positional candidates for bipolar disorder.

Several studies have proposed the existence of susceptibility loci for bipolar disorder on chromosome 18. To identify possible candidate genes for this disease, we isolated brain-expressed transcripts by direct cDNA selection on chromosome 18-specific biotinylated cosmid clones. Longer cognate cDNA clones of the selected cDNAs were isolated from a normalized infant brain cDNA library. Physical mapping by PCR on a panel of somatic cell hybrids was conducted by the use of primers derived from partial sequences on either the 5' or 3' ends of the clones. In our initial analysis, 48 cDNA clones were found to be chromosome 18-specific, mapping to different subchromosomal regions. Sequence redundancy among these clones yielded 30 unique transcripts, five of which were represented in previously known genes. Further sequencing of the remaining 25 unique cDNA clones confirmed the absence of significant homology to known genes, indicating that these transcripts represented novel genes. Mapping with the use of a radiation hybrid panel positioned the brain cDNAs to within = 100 to 1100 kb from reference sequence tag sites (STSs) and assembled them into six high resolution linkage groups. The majority of the transcripts were found to cluster to discrete locations on 18p and 18q, previously hypothesized as susceptibility regions for bipolar disorder, identifying them as positional candidate genes.

Association study of schizophrenia and the dopamine D3 receptor gene locus in two independent samples.

Using a case-control design, an association of schizophrenia with the dopamine D3 receptor gene (D3RG) locus was investigated. Initial analysis of pooled results from published studies revealed a significant excess of individuals homozygous for either allele among the patients. The association was next tested in two cohorts ascertained independently at Pittsburgh, Pennsylvania and at Houston, Texas. The Pittsburgh sample was comprised of patients with schizophrenia (DSM-III-R) (n = 130). The controls belonged to two groups: adults screened for the absence of substance abuse or major psychiatric illness (n = 128), and neonates (n = 160). Multivariate analysis suggested an association with allele 1 of the biallelic D3RG polymorphism in comparison with the adult, but not the neonatal, controls. The association was most marked among Caucasian patients with a family history of schizophrenia (odds ratio 13.69, confidence intervals 1.80, 104.30). Survival analysis suggested an earlier age of onset among male patients homozygous for allele 2. The Houston cohort included Caucasian patients with schizophrenia or schizoaffective disorder (DSM-III-R criteria, n = 50), and normal controls matched for gender (n = 51). In this group, no significant associations were noted among all the patients or among subgroups of patients based on family history or age of onset. Possible reasons for the discordant results are discussed.

Initial genome scan of the NIMH genetics initiative bipolar pedigrees: chromosomes 4, 7, 9, 18, 19, 20, and 21q.

An initial genome scan was performed on 540 individuals from 97 families segregating bipolar disorder, collected through the National Institutes of Mental Health Genetics Initiative. We report here affected-sib-pair (ASP) data on 126 marker loci (approximately 68,000 genotypes) mapping to chromosomes 4, 7, 9, 18, 19, 20, and 21q, under three affection status models. Modest increases in identical-by-descent (IBD) allele sharing were found at the following loci: D4S2397 and D4S391 (P < 0.05) on 4p, D4S1647 (P < 0.05) on 4q, D7S1802 and D7S1869 (low P = 0.01) on 7p, D9S302 (P = 0.004) on 9q, and D20S604 on 20p and D20S173 on 20q (P < 0.05). In addition, five markers on 7q displayed increased IBD sharing (P = 0.046-0.002). Additional ASP analyses on chromosomes 18 and 21q marker data were performed using disease phenotype models defined previously. On chromosome 18, only D18S40 on 18p and D18S70 on 18q yielded a slight elevation in allele sharing (P = 0.02), implying that the reported linkages in these regions were not confirmed. On chromosome 21q, a cluster of markers within an approximately 9 cM interval: D21S1254, D21S65, D21S1440, and D21S1255 exhibited excess allele sharing (P = 0.041-0.008). Multilocus data on overlapping marker quartets, from D21S1265 to D21S1255, which were consistent with increased IBD sharing (P < 0.01, with a low of 0.0009), overlapped a broad interval of excess allele sharing reported previously, increasing support for a susceptibility locus for bipolar disorder on 21q.

Follow-up study on a susceptibility locus for schizophrenia on chromosome 6q.

Evidence for suggestive linkage to schizophrenia with chromosome 6q markers was previously reported from a two-stage approach. Using nonparametric affected sib pairs (ASP) methods, nominal p-values of 0.00018 and 0.00095 were obtained in the screening (81 ASPs; 63 independent) and the replication (109 ASPs; 87 independent) data sets, respectively. Here, we report a follow-up study of this 50cM 6q region using 12 microsatellite markers to test for linkage to schizophrenia. We increased the replication sample size by adding an independent sample of 43 multiplex pedigrees (66 ASPs; 54 independent). Pairwise and multipoint nonparametric linkage analyses conducted in this third data set showed evidence consistent with excess sharing in this 6q region, though the statistical level is weaker (p=0.013). When combining both replication data sets (total of 141 independent ASPs), an overall nominal p-value=0.000014 (LOD=3. 82) was obtained. The sibling recurrence risk (lambdas) attributed to this putative 6q susceptibility locus is estimated to be 1.92. The linkage region could not be narrowed down since LOD score values greater than three were observed within a 13cM region. The length of this region was only slightly reduced (12cM) when using the total sample of independent ASPs (204) obtained from all three data sets. This suggests that very large sample sizes may be needed to narrow down this region by ASP linkage methods. Study of the etiological candidate genes in this region is ongoing.

Association between genetic variation at the porphobilinogen deaminase gene and schizophrenia.

There is growing evidence that some genetic predisposition is important in the etiology of schizophrenia. We have sought to implicate a major gene by performing a candidate gene association study comparing the allele frequencies of seven restriction fragment length polymorphisms (RFLPs) at six loci in both a psychiatrically normal control group (N = 51) and an affected (schizophrenia or schizoaffective disorder) group (N = 55). Each group comprised Caucasians of northern European origin. The candidate areas (D5S39, D5S78, dopamine receptor D2 (DRD2), D11S29, porphobilinogen deaminase (PBGD), and D11S84) were selected on the basis of prior cytogenetic findings in schizophrenics, linkage studies, and/or implicated gene products. The presence of a polymorphic ApaLI site within the PBGD gene showed a significant association with the presence of illness (P = 0.02). The relative risk of possessing the allele with the ApaLI site was 2.10. No significant association was found with any of the six other RFLPs. Our data suggests that either the PBGD gene itself or an unknown gene linked to and/or in linkage disequilibrium with the PBGD locus predisposes some individuals to schizophrenia. Independent replication of these findings will be required to determine their relevance to schizophrenia.

Haplotypic association spanning the 22q11.21 genes COMT and ARVCF with schizophrenia.

Catechol-O-methyltransferase (COMT) has been implicated in schizophrenia by its function through its roles in monoamine neurotransmitter metabolism and its impact on prefrontal cognition, and also by its position through linkage scans and a strong cytogenetic association. Further support comes from association studies, especially family-based ones examining the COMT variant, Val(108/158)Met. We have studied eight markers spanning COMT and including portions of the two immediately adjacent genes, thioredoxin reductase 2 and armadillo repeat deleted in velocardiofacial syndrome (ARVCF), using association testing in 136 schizophrenia families. We found nominal evidence for association of illness to rs165849 (P=0.051) in ARVCF, and a stronger signal (global P=0.0019-0.0036) from three-marker haplotypes spanning the 3' portions of COMT and ARVCF, including Val(108/158)Met with Val(108/158) being the overtransmitted allele, consistent with previous studies. We also find Val(108/158)Met to be in linkage disequilibrium with the markers in ARVCF. These findings support previous association signals of schizophrenia to COMT markers, and suggest that ARVCF might contribute to this signal. ARVCF, a member of the catenin family, besides being a positional candidate, is also one due to its function, that is, its potential role in neurodevelopment, which is implicated in schizophrenia pathogenesis by several lines of evidence.

Complexities in psychiatric genetics.

A substantial contribution of genetic factors to the risk of psychiatric disorders such as schizophrenia, bipolar disorder, autism, and drug and alcohol dependence has already been established. However, the familial transmission of these disorders cannot be explained by simple Mendelian models of inheritance, and non-genetic factors must also play a substantial role in their etiologies. Furthermore, the prevalence of any major psychiatric disorder is a great deal higher than that of Mendelian disorders. It has been suggested that evolutionary forces would rapidly eliminate large gene effects, which would suggest that mental disorders, which are highly prevalent, are associated with minor gene effects (Risch, 1994). The current paradigm is that genes with small interacting genetic effects, in conjunction with environmental factors, affect the risk for psychiatric disease. New laboratory and statistical methodology and database tools, and the availability of large clinical samples for the study of linkage and association sustain optimism that genes involved with these diseases will be characterized in the near future. This accomplishment should in turn lead not only to a better understanding of the primary molecular pathophysiology and to more specific and effective therapies, but also to a better understanding of non-genetic risk factors that could be targets for preventive strategies.