Incidence of RET mutations in patients with Hirschsprung's disease

Background: RET mutations have been reported variously to affect 7% to 41% of Hirschsprung's disease (HSCR) patients depending on familial or sporadic occurrence of the disease, length of aganglionosis and possible associatio n with other disease phenotypes. The authors report a study of the incidenc e of RETmutations in unselected HSCR patients from two regional centers and correlate their genotypes and phenotypes. Methods: The records of HSCR patients treated in 2 regional centers with a combined population of 5 million were reviewed, and blood samples were obta ined from 57 patients. During the same period, 39 patients with similar dem ographic data refused or provided insufficient blood for study. DNA was ext racted, and the 21 exons of the RET protooncogene were screened for mutatio ns using denaturing gradient gel electrophoresis (DGGE). Results: Of 57 patients, 48 were sporadic, and 9 were familial. Lengths of aganglionosis were total colonic, 4; long, 11; short, 39; ultrashort, 1; un classified, 2. Associated anomalies were present in 20, Causative mutations were identified in 4 (7%): missense or "silent" in 3 (exons 5, 11, 13) and deletion in 1. The silent mutation of exon 11 recently has been shown to h ave effects on correct RET mRNA splicing. One mutation occurred in total co lonic aganglionosis (25%), 1 in long segment dysganglionosis (9%), and 2 in short segment aganglionosis (5%). Surprisingly, all these mutations occurr ed in sporadic cases (10%). Five patients (9%) had rare polymorphic alleles at exon 14 (n = 1) and exon 18 (n = 4). Fifty patients (88%) showed common polymorphic alleles (sequence variants) in 1 or more exons (>4, n = 5). Conclusions: RET mutation as a primary cause for Hirschsprung's disease in the general surgical population is less frequent than previously thought. T his observation is compatible with the hypothesis that HSCR could be a poly genic disease caused by additive subclinical effects of more than one gene, including RET.