Identification of rare variants in the NRG1 gene of Hirschsprung's patients

Abstract

Hirschsprung’s disease (HSCR, aganglionic megacolon), is a congenital disorder characterized by the absence of enteric ganglia in variable portions of the distal intestine. HSCR has a complex pattern of inheritance and presents mainly sporadically. Besides the major HSCR gene, RET, and other implicating genes (e.g. EDNRB), there is evidence that other loci contribute to HSCR. Recently, through a genome-wide association study, we identified NRG1 as a new HSCR contributing locus. Several lines of evidence indicate that in addition to common variants/SNPs, rare variants may contribute substantially to the multifactorial inheritance of complex diseases, and that the genes with disease-associated SNPs are to be considered candidates for the search of deleterious rare variants. We hypothesized that rare NRG1 variants contributing to HSCR may exist. To identify these variants, we have sequenced the 17 exons (including exon/intron boundaries) of NRG1 of 386 HSCR patients and 100 controls on an ABI 3730xl DNA Analyzer. We have identified 7 novel rare variants in 7 patients that cause 4 non-synonymous amino-acid changes, a truncation of the protein, a disruption of the splice site and an alteration of the conserved region intronic region in the exon boundary. The non-synonymous amino-acid substitutions affect highly conserved residues and have not been found in the controls. The four patients bearing NRG1 rare variants have no diseaseassociated variants in RET or any other HSCR-associated gene. The finding of rare NRG1 variants with an obvious functional effect on the NRG1 protein, suggest that NRG1 is one of the several molecules contributing to the pathology of HSCR. More controls are currently being sequenced.