Study of two bipolar susceptibility genes: Slynar and IGF1 .

Abstract

Linkage studies have implicated the 12q22-24 region in susceptibility to bipolar disorder. In this region alleles at the “Slynar” and Insulin Like Growth Factor 1 (IGF1) genes showed association with bipolar disorder. The Slynar gene is contained within a region of 278 kb on chromosome 12q24 and expresses the sequence AY070435 in the human brain. AY070435 has no known function. A Macaque brain expressed cDNA which is highly homologous to human AY070435 has been cloned and sequenced. To further characterise the human Slynar gene and expressed mRNA transcript studies were carried out to identify Slynar in the mouse and in human neuroblastoma cell lines. Exhaustive efforts were taken to find a mouse homologue but these proved negative. Slynar shared no homology, or partial homology with any other gene in the human genome. The other 12q24 bipolar susceptibility gene IGF1 is highly expressed in the human brain and a well known for its neuromodulatory functions. IGF1 protein has been shown to have an antidepressant and anxiolytic-like effect in the mouse brain. On a genome wide association study (GWAS) with the UCL case control sample, IGF1 was found to be associated to disease with 5 SNPs showing association within the gene. In order to further implicate IGF1 and find the aetiological base pair changes responsible for disease, IGF1 was sequenced. New three new non database SNPs, three previously characterised polymorphisms and a CA repeat were found and genotyped in an extended UCL sample of 1,000 cases and 1,000 controls. One of the novel SNPs and the CA repeat, both located in the promoter region, were associated with bipolar disorder. Haplotype analysis of the GWAS and new markers data confirmed association to bipolar disorder.