D Dempster

Novel mutations in 5-HT3A and 5-HT3B receptor genes not associated with clozapine response

Clozapine is a potent antagonist of 5-HT3 receptors, which are ligand-gated ion channels that mediate rapid excitatory responses in the central nervous system. Two different isoforms of 5-HT3 receptor subunit genes (HTR3A and HTR3B) have been identified. They have been assigned to chromosome 11q23.1-q23.2, a region which in the past has been linked to schizophrenia and bipolar disorder. In this study, we performed a systematic mutation screening of the 5-HT3A and 5-HT3B receptor genes and tested the variants for association with clozapine response in a sample of 266 clozapine-treated patients. Two polymorphisms at the 5-HT3A gene and five new variants in the 5-HT3B gene were finally detected. Of these, only the more frequent mutations (178-C/T and 1596-A/G in 5-HT3A and a CA-repeat in 5-HT3B) were genotyped in our clozapine sample. Association analysis showed similar allele and genotype distributions among clozapine responders and nonresponders. These results make unlikely the possibility that 5-HT3A and 5-HT3B receptor genes underlie variation in clinical response to clozapine. However, the promoter regions of both genes have yet to be investigated.

Gene-expression analysis of clozapine treatment in whole blood of patients with psychosis

Objectives Clozapine is an atypical antipsychotic primarily prescribed for treatment-resistant schizophrenia. We tested the specific effect of clozapine versus other drug treatments on whole-blood gene expression in a sample of patients with psychosis from the UK. Methods A total of 186 baseline whole-blood samples from individuals receiving treatment for established psychosis were analysed for gene expression on Illumina HumanHT-12.v4 BeadChips. After standard quality-control procedures, 152 samples remained, including 55 from individuals receiving clozapine. In a within-case study design, weighted gene correlation network analysis was used to identify modules of coexpressed genes. The influence of mood stabilizers, lithium carbonate/lithium citrate and sodium valproate was studied to identify their possible roles as confounders. Results Individuals receiving clozapine as their only antipsychotic (clozapine monotherapy) had a nominal association with one gene-expression module, whereas no significant change in gene expression was found for other drugs. Conclusion Overall, this study does not provide evidence that clozapine treatment induces medium to large different gene-expression patterns in human whole blood versus other antipsychotic treatments. This does not rule out the possibility of smaller effects as observed for other common antipsychotic treatments.

Immune signatures and disorder-specific patterns in a cross-disorder gene expression analysis

Background Recent studies point to overlap between neuropsychiatric disorders in symptomatology and genetic aetiology. Aims To systematically investigate genomics overlap between childhood and adult attention-deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD) and major depressive disorder (MDD). Method Analysis of whole-genome blood gene expression and genetic risk scores of 318 individuals. Participants included individuals affected with adult ADHD (n = 93), childhood ADHD (n = 17), MDD (n = 63), ASD (n = 51), childhood dual diagnosis of ADHD–ASD (n = 16) and healthy controls (n = 78). Results Weighted gene co-expression analysis results reveal disorder-specific signatures for childhood ADHD and MDD, and also highlight two immune-related gene co-expression modules correlating inversely with MDD and adult ADHD disease status. We find no significant relationship between polygenic risk scores and gene expression signatures. Conclusions Our results reveal disorder overlap and specificity at the genetic and gene expression level. They suggest new pathways contributing to distinct pathophysiology in psychiatric disorders and shed light on potential shared genomic risk factors.

Investigation of common, low-frequency and rare genome-wide variation in anorexia nervosa

Anorexia nervosa (AN) is a complex neuropsychiatric disorder presenting with dangerously low body weight, and a deep and persistent fear of gaining weight. To date, only one genome-wide significant locus associated with AN has been identified. We performed an exome-chip based genome-wide association studies (GWAS) in 2158 cases from nine populations of European origin and 15 485 ancestrally matched controls. Unlike previous studies, this GWAS also probed association in low-frequency and rare variants. Sixteen independent variants were taken forward for in silico and de novo replication (11 common and 5 rare). No findings reached genome-wide significance. Two notable common variants were identified: rs10791286, an intronic variant in OPCML (P=9.89 × 10−6), and rs7700147, an intergenic variant (P=2.93 × 10−5). No low-frequency variant associations were identified at genome-wide significance, although the study was well-powered to detect low-frequency variants with large effect sizes, suggesting that there may be no AN loci in this genomic search space with large effect sizes.