Association between c135G/A genotype and RET proto-oncogene germline mutations and phenotype of Hirschsprung's disease

Background: Several genes, including the major susceptibility gene RET, have roles in development of Hirschsprung's disease. Results of genetic-linkage analysis of patients with familial disease with both long-segment and short-segment phenotypes have shown close linkage with the RET locus. We aimed to investigate whether both RET mutations and polymorphisms contribute to phenotype of Hirschsprung's disease. Methods: We looked at the coding region of all 21 exons of the RET proto-oncogene, including the flanking intronic sequences, by direct DNA sequencing in 76 caucasians from Germany with Hirschsprung's disease. Findings: 20 different mutations were detected in 18 patients. Mutations were under-represented in patients with a homozygous RET c135A/A genotype in association with short-segment phenotype. Short-segment phenotype also arose if the RET mutation was on the c135A allele; conversely, a RET germline mutation on the c135G allele resulted in long-segment phenotype, particularly in heterozygous c135G/A patients. Interpretation: These observations lend support to the idea that both RET alleles have a role in pathogenesis of Hirschsprung's disease, in a dose-dependent fashion. We also showed that the c135G/A polymorphism modifies the phenotype by a within-gene interaction between the c135A variant and a mutation.