RET mutational spectrum in Hirschsprungs disease: evaluation of 601 Chinese patients

Abstract

Hirschsprung’s disease (HSCR) is a developmental disorder characterized by the absence of ganglion cells in the lower digestive tract. Aganglionosis is attributed to a disorder of the enteric nervous system (ENS) whereby ganglion cells fail to innervate the lower gastrointestinal tract during embryonic development. There is significant population variation in the incidence of the disease, and it is most often found among Asians (2.8 per 10,000 live births). HSCR most commonly presents sporadically (80% of the cases), with a recurrence risk of 4%, and more males than females affected (4:1). Both rare (<1% in the population) and common germ line variants of the RET gene, acting either alone or in combination, are the main cause of the disease. Yet, while RET common variants are strongly associated with the commonest manifestation of the disease (male, short segment, and sporadic forms), rare coding sequence (CDS) variants are more frequently found in the lesser common and more severe forms of the disease (females, long or total colonic aganglionosis, and familial). Here we present a rare variant (RV) screening of the CDS and intron/exon boundaries of the RET gene in 607 Chinese sporadic HSCR patients, the largest number of patients ever reported. We have found a total of 61 different heterozygous RVs (50 novel) distributed in 100 patients (16.64%). These include 14 silent, 29 missense, 5 nonsense amino-acid changes, 4 frame-shifts, and one in-frame amino-acid deletion in the exonic region and two splice-site deletions, 4 nucleotide substitutions and a 22 bp deletion in intronic or untranslated regions. The exonic variants were mainly clustered in the sequence encoding the extracellular domain of the RET protein. All RVs were predicted to alter the protein function. The highest frequency of rare variants was found among those patients with the most severe form of the disease (24% in long or total vs 15% in short-segment). Phasing of the RVs with the RET risk-haplotype suggested that RET RVs do not underlie the undisputable association of RET common variants with HSCR. None of the variants was found in 250 Chinese controls.