GWAS for Bipolar Disorder in a European Cohort with CNV Discovery

A Thesis submitted to The University of Arizona College of Medicine - Phoenix in partial fulfillment of the requirements for the Degree of Doctor of Medicine.

Background: Bipolar disorder (BD) is a disabling disorder whereby individuals suffer from episodes of mania and depression. The mode of inheritance of BD is complex and likely multifactorial. The specific number of susceptibility loci, the recurrence risk ratio attributable to each locus, and the degree of interaction between loci are unknown. By determining whether single nucleotide polymorphisms (SNPs) or copy number variants (CNVs) predispose individuals to bipolar disorder, therapeutics and diagnostic tests may be developed. Method: A Genome Wide Association Study (GWAS) was performed using cases of bipolar disorder and normal controls hybridized on Affymetrix 6.0 Genome-Wide Human SNP Arrays. Data preprocessing removed 595 individuals from 2205 arrays. The probe intensities of the remaining 880 cases and 730 controls were normalized. A modified t-test algorithm was used to determine p-values for each SNP. A sliding window analysis was performed on SNPs ordered by chromosome and locus. The mean probe intensities of the cases and controls from regions of significance were then reanalyzed for differences. Results: Analysis yielded several SNPs and CNVs that may have involvement in the pathophysiology of bipolar disorder. One region was 15kbp within the Neuron Navigator 2 (NAV2) gene. A second region was found in the Down Syndrome Cell Adhesion Molecule Like 1 (DSCAML1) gene. A third region was within the Voltage-dependent Calcium Channel Alpha 1G (CACNA1G). Conclusion: Multiple SNPs and CNVs may play a role in the phenotype of Bipolar Disorder. A convergent functional genomics approach with a gene network analysis maybe warranted elucidating possible pathophysiologies involving the gene products found to be significant in this study.