Abstract
The Ashkenazi Jewish population has a several-fold higher prevalence of Crohn's disease (CD) compared with non-Jewish European ancestry populations and has a unique genetic history. Haplotype association is critical to CD etiology in this population, most notably at NOD2, in which three causal, uncommon and conditionally independent NOD2 variants reside on a shared background haplotype. We present an analysis of extended haplotypes that showed significantly greater association to CD in the Ashkenazi Jewish population compared with a non-Jewish population (145 haplotypes and no haplotypes with P-value <10(-3), respectively). Two haplotype regions, one each on chromosomes 16 and 21, conferred increased disease risk within established CD loci. We performed exome sequencing of 55 Ashkenazi Jewish individuals and follow-up genotyping focused on variants in these two regions. We observed Ashkenazi Jewish-specific nominal association at R755C in TRPM2 on chromosome 21. Within the chromosome 16 region, R642S of HEATR3 and rs9922362 of BRD7 showed genome-wide significance. Expression studies of HEATR3 demonstrated a positive role in NOD2-mediated NF-κB signaling. The BRD7 signal showed conditional dependence with only the downstream rare CD-causal variants in NOD2, but not with the background haplotype; this elaborates NOD2 as a key illustration of synthetic association.