Abstract WP160: Exome Array Analysis of Early-Onset Ischemic Stroke

Background: The genetic architecture of ischemic stroke (IS) is poorly understood and may differ by age of onset. To identify stroke susceptibility variants, genes and pathways for IS in young adults, we genotyped participants in the Genetics of Early-Onset Stroke (GEOS) with an exome array to interrogate the protein-coding portion of genes. Methods: The GEOS Study was initiated as a biracial population-based study of cases with first-ever ischemic stroke 15 to 49 years of age (n=828) and controls (n=850). All participants had prior GWAS and underwent Illumina exome-chip genotyping. Mixed model regression in EMMAX was conducted to calculate variant-specific associations using pooled European-Caucasians (EUR) and African-Americans (AA) samples, with population structure controlled by kinship matrix relationships using GWAS data. Gene-based burden testing and meta-analysis were performed using seqMeta with ethnicity-specific GWAS PCs. In both analyses covariates included age and gender. This was followed by Ingenuity Pathway Analyses on the top genes. Results: While no individual SNPs reached chip-wide significance (3x10 -7 ), several were near, including one exonic variant in TRAPPC11 (rs67383011, p=1.7*10 -6 ). Gene-based burden testing using a filter (cumulative MAC>40, # of SNPs per gene≥2, missingness=0) was performed on 6934 genes in EURs and 9423 genes in AAs. While several interesting genes were identified, notably in methylation pathways, none reached statistical significance in the ethnicity-stratified (p=3.3*10 -4 ) or meta-analyses (p=1.1*10 -4 ). Pathway analyses on the top 448 genes (p<0.05) from the gene-based results identified several metabolism and signaling pathways, including: (1) those implicated in the risk for vascular diseases: glucose metabolism, lipid metabolism, and inflammation (leukocyte extravasation, IL-17A); (2) neurotrophic signaling: CTNF and NGF, and; (3) neurotransmitter and neuroactive compound signaling: GABA receptor signaling and tryptophan degradation pathways. Efforts in additional data sets to replicate these findings are ongoing. Conclusion: Exome-based analyses in the setting of early-onset stroke is a promising methodology to identify novel genetic risk variants, loci and pathways.