Admixture Mapping of Sarcoidosis Genes in African American

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Sarcoidosis, a multiorgan granulomatous inflammatory disease, likely results from an exaggerated T cell response to an airborne antigen. A genetic predisposition to sarcoidosis has long been posited, and recent independent genome scans in German and African-American affected sib pair samples suggest that multiple genes are involved. African-Americans are more commonly and severely affected by sarcoidosis, which imply that genes of African ancestry play a significant role in the disease etiology and pathogenesis. Recent characterization of ancestry informative markers across the genome now makes it feasible to scan the genome for disease genes linked to ancestry in African-American populations. As a research group that has extensively studied the genetic susceptibility of sarcoidosis in African Americans, we have accumulated DMA samples for 1,026 unrelated African American sarcoidosis cases. Many of these cases have participated in one of three previous NIH-funded studies, two family studies and one case-control, that provide a wealth of clinical and epidemiologic data in addition to a DNA sample. From the ACCESS case-control study we also have DNA and epidemiologic data on 305 unrelated African Americans without sarcoidosis who will serve as a control sample. Using these samples, we propose a mapping by admixture linkage disequilibrium (MALD) study to identify sarcoidosis genes linked to African ancestry. The study will involve a multi-staged genome-wide scan targeting specifically those genes of African origin in African Americans that predispose to sarcoidosis susceptibility and radiographically persistent disease. We plan to first screen the genome using a set of 1,536 SNP markers evenly spaced approximately 1.9 cM throughout the genome that are highly informative European - African ancestry differences. In the second stage, we will triple density genotype ancestry informative markers to increase statistical confidence in the results and refine the positions. We will then move to a targeted haplotypebased association study in the most interesting regions. Once we have narrowed the associated genomic areas to specific genes or areas within specific genes, we will sequence the areas that have the highest probability of harboring causal variant(s). In addition, to better understand how putative candidate genes we identify act in sarcoidosis causal pathways involving environmental inciting agents, we will utilize comparable environmental data collected across the three study samples to test for geneenvironment interaction. Our proposed study has the potential to uncover genes of modest effect not easily detectable by linkage and may in some instances actually be more statistically powerful than traditional case-control association methods.