Localizing a putative mutation as the major contributor to the development of sporadic Hirschsprung disease to the RET genomic sequence between the promoter region and exon 2

Abstract

Hirschsprung disease (HSCR), a congenital disorder characterized by intestinal obstruction due to absence of enteric ganglia along variable lengths of the intestinal tract, occurs both in familial and sporadic cases. RET mutations have been found in approximately 50% of the families, but explains only a minority of sporadic cases. This study aims at investigating a possible role of RET in sporadic HSCR patients. Haplotypes of 13 DNA markers, within and flanking RET, have been determined for 117 sporadic HSCR patients and their parents. Strong association was observed for six markers in the 5 0 region of RET. The largest distortions in allele transmission were found at the same markers. One single haplotype composed of these six markers was present in 55.6% of patients versus 16.2% of controls. Odds ratios (ORs) revealed a highly increased risk of homozygotes for this haplotype to develop HSCR (OR420). These results allowed us to conclude that RET plays a crucial role in HSCR even when no RET mutations are found. An unknown functional disease variant(s) with a dosage-dependent effect in HSCR is likely located between the promoter region and exon 2 of RET.

Current concepts in RET-related genetics, signaling and therapeutics

“…The same diseaseassociated haplotype was observed in the 5 0 region of the RET locus in 56-62% individuals of European descent (including Americans) [48][49][50][51][52][53][54][55]. The same haplotype was also present in Asians, although at a much higher frequency (85%) [52,54].…”

“…In addition, most of the individuals found to carry the Hirschsprung haplotype were homozygous for it. Because individuals who are homozygous for the disease-associated haplotype have a tenfold higher risk of developing the disease than heterozygous carriers, a dose-dependent action of the unknown mutation has been suggested [51].…”

“…Seventy per cent of double homozygotes for Ret 51 and Et-3 ls (the null allele of the ligand of Ednrb) developed total intestinal aganglionosis, again indicating a strong interaction between these two loci [62]. cAMP-dependent protein kinase A (PKA) has been pinpointed as a likely candidate that mediates interactions between the RET and EDNRB pathways, because inhibition of PKA mimics the effect of ET-3 (proliferation and inhibition of migration) on neural crest cells (NCCs) [60].…”

Evaluation of the role of RET polymorphisms/haplotypes as modifier loci for MEN 2, and analysis of the correlation with the type of RET mutation in a series of Spanish patients

“…Moreover, we have also selected two SNPs at -5 and -1 from the transcriptional start site (-200A➝G and -196C➝A), given that results derived from luciferase expression assays have shown differential activities for their different combinations (AC, GC and GA), suggesting a role of those variants in the transcriptional regulation of RET (29,42,43). Thus, we postulated that the two polymorphisms may also exert a modifier effect on MEN 2 phenotypes.…”

Low RET mutation frequency and polymorphism analysis of the RET and EDNRB genes in patients with Hirschsprung disease in Taiwan

“…Generally, RET is the major susceptibility gene of HSCR, with incomplete penetrance. Beside the mutations in the RET coding regions, specific polymorphisms or haplotypes of RET (Borrego et al 2000;Borrego et al 2003;Burzynski et al 2004;Fitze et al 1999;Fitze et al 2003;Garcia-Barcelo et al 2003;Griseri et al 2002) and variations at the RET locus, together with variations at unknown loci on 3p21 and 19q12 (Gabriel et al 2002), have all been proposed to account for the genetic susceptibility to HSCR. In this study, significant deviation of random transmission of the A allele of c135G>A, the G allele of c1296G>A, and the G allele of c2307T>G, indicates that these alleles are in strong linkage disequilibrium with the disease-causing alleles.…”