Mutations in the NRG1 gene are associated with Hirschsprung disease.

Hirschsprung disease (HSCR, congenital colon aganglionosis) is a relatively common complex genetic condition caused by abnormal development of the enteric nervous system (ENS). Through a recent genome-wide association study conducted on Chinese HSCR patients, we identified a new HSCR contributing locus, neuregulin 1 (NRG1; 8p12), a gene known to be involved in the development of the ENS. As genes in which disease-associated common variants are found are to be considered as candidates for the search of deleterious rare variants (RVs) in the coding sequences, we sequenced the NRG1 exons of 358 sporadic HSCR patients and 333 controls. We identified a total of 13 different heterozygous RVs including 8 non-synonymous (A28G, E134K, V266L, H347Y, P356L, V486M, A511T, P608A) and 3 synonymous amino acid substitutions (P24P, T169T, L483L), a frameshift (E239fsX10), and a c.503-4insT insertion. Functional analysis of the most conserved non-synonymous substitutions, H347Y and P356L, showed uneven intracellular distribution and aberrant expression of the mutant proteins. Except for T169T and V486M, all variants were exclusive to HSCR patients. Overall, there was a statistically significant over-representation of NRG1 RVs in HSCR patients (p = 0.008). We show here that not only common, but also rare variants of the NRG1 gene contribute to HSCR. This strengthens the role of NRG1.

Fine mapping of the NRG1 Hirschsprung's disease locus.

The primary pathology of Hirschsprung's disease (HSCR, colon aganglionosis) is the absence of ganglia in variable lengths of the hindgut, resulting in functional obstruction. HSCR is attributed to a failure of migration of the enteric ganglion precursors along the developing gut. RET is a key regulator of the development of the enteric nervous system (ENS) and the major HSCR-causing gene. Yet the reduced penetrance of RET DNA HSCR-associated variants together with the phenotypic variability suggest the involvement of additional genes in the disease. Through a genome-wide association study, we uncovered a ∼350 kb HSCR-associated region encompassing part of the neuregulin-1 gene (NRG1). To identify the causal NRG1 variants contributing to HSCR, we genotyped 243 SNPs variants on 343 ethnic Chinese HSCR patients and 359 controls. Genotype analysis coupled with imputation narrowed down the HSCR-associated region to 21 kb, with four of the most associated SNPs (rs10088313, rs10094655, rs4624987, and rs3884552) mapping to the NRG1 promoter. We investigated whether there was correlation between the genotype at the rs10088313 locus and the amount of NRG1 expressed in human gut tissues (40 patients and 21 controls) and found differences in expression as a function of genotype. We also found significant differences in NRG1 expression levels between diseased and control individuals bearing the same rs10088313 risk genotype. This indicates that the effects of NRG1 common variants are likely to depend on other alleles or epigenetic factors present in the patients and would account for the variability in the genetic predisposition to HSCR.