RET genotypes comprising specific haplotypes of polymorphic variants predispose to isolated Hirschsprung disease

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Abstract
BACKGROUND Hirschsprung disease (HSCR), which may be sporadic or familial, occurs in 1:5000 live births and presents with functional intestinal obstruction secondary to aganglionosis of the hindgut. Germline mutations of theRET proto-oncogene are believed to account for up to 50% of familial cases and up to 30% of isolated cases in most series. However, these series are highly selected for the most obvious and severe cases and large familial aggregations. Population based studies indicate that germline RETmutations account for no more than 3% of isolated HSCR cases. Recently, we and others have noted that specific polymorphic sequence variants, notably A45A (exon 2), are over-represented in isolated HSCR. PURPOSE In order to determine if it is the variant per se, a combination thereof, or another locus in linkage disequilibrium which predisposes to HSCR, we looked for association of RET haplotype(s) and disease in HSCR cases compared to region matched controls. METHODS Seven loci acrossRET were typed and haplotypes formed for HSCR cases, their unaffected parents, and region matched controls. Haplotype and genotype frequencies and distributions were compared among these groups using the transmission disequilibrium test and standard case-control statistic. RESULTS Twelve unique haplotypes, labelled A-L, were obtained. The distributions of haplotypes between cases and controls (χ11 2 =81.4, p<2 11=53.1, p37 2=93.8, pCONCLUSIONS Our data suggest that genotypes comprising specific pairs of REThaplotypes are associated with predisposition to HSCR either in a simple autosomal recessive manner or in an additive, dose dependent fashion.