Fine mapping 8q24 in Familial Bipolar Disorder

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DESCRIPTION (provided by applicant): This is a revised proposal that aims to identify the susceptibilitygene or genomic region located on chromosome 8q24 associated with bipolar disorder. It uses association-based methods to identify an association in a family sample and replicate the association in a case/control design. There is good evidence for a susceptibility gene on 8q24. We reported a parametric 2-pt LOD of 3.32 at D8S256 on 8q24 in 65 multiplex bipolar families, which is significant, genome-wide. We are collaborating with investigators at the U. Antwerp who also have genome-wide evidence of linkage to 8q24. Our replication sample will be derived from the pedigrees of NIMH Genetics Initiative for Bipolar disorder (NiMH-GI BP). We will select cases from NIMH-GI BP families with evidence of increased allele sharing around the D8S256 locus, using recently published methods, implemented in the genetic analytic program, Merlin, thereby enriching our replication sample for 8q24 genetic cases. Preliminary analysis finds 284 pedigrees with increased allele sharing on 8q24 in NIMH-GI BP. We will use a similar number of controls ascertained under the auspices of the NIMH-GI. Investigators at the U Antwerp are also actively pursuing this region and they have agreed to test our positive association findings in their sample. This is attractive because the Antwerp sample is predominantly of N. European origin, similar to the Hopkins and NIMH samples. Preliminary power analyses based on the actual pedigree structure and our case/control design find that the sample is sufficientto meet our thresholds, requiring significance p<0.001 in the family based analysis and p< 0.01 in the NIMH-GI case/control sample. We have added a third significance threshold level of p<0.01 in the Antwerp sample. Meeting these standards would make a compelling argument for the presence of a susceptibility gene in this vicinity. We propose SNP genotyping on an industrial scale, using Illumina array-based technology now available at Hopkins, placing 1,536 SNPs in a 14 Mb region, with an average of 10 kb interval between SNPs. We will begin with genotyping the Hopkins/Dana sample, and follow-up the positive regions in the case/control sample derived from the linked NIMH-GI BP pedigrees. Significant associations from these analyses would subsequently be tested in the Antwerp sample (no funding requested for Antwerp). If the region is replicated we would begin sequencing around the peak in affected subjects from the Hopkins and NIMH samples that carry the risk allele or haplotype, the goal being to identify all SNP variants immediately adjacent to the replicated result. The variants identified in sequencing would then be typed in larger samples, which by the conclusion of this proposal will include the subjects from the current NIMH-GI 5,000 BP case ascertainment. With the identification, replication and characterization of the association for BP and 8q24 we will be in a strong positionto pursue further gene and functional studies.