Comprehensive analysis of RET common and rare variants in a series of Spanish Hirschsprung patients confirms a synergistic effect of both kinds of events

RET mutational screening was performed by dHPLC and direct sequencing for the identification of RVs. In addition Taqman technology was applied for the genotyping of 3 RET CVs previously associated to HSCR, including a variant lying in an enhancer domain within RET intron 1 (rs2435357). Statistical analyses were performed using the SPSS v.17.0 to analyze the distribution of the variants.Our results confirm the strongest association to HSCR for the "enhancer" variant, and demonstrate a significantly higher impact of it in male versus female patients. Integration of the RET RVs and CVs analysis showed that in 91.66% of cases with both kinds of mutational events, the enhancer allele is in trans with the allele bearing the RET RV.A gender effect exists on both the transmission and distribution of rare coding and common HSCR causing mutations. In addition, these RET CVs and RVs seem to act in a synergistic way leading to HSCR phenotype.Hirschsprung disease (HSCR, OMIM #142623) is a congenital malformation of the hindgut produced by a disruption in the neural crest cells (NCC) migration during embryonic development. This disorder results in an absence of intramural ganglion cells in the submucosal and myenteric plexuses producing a functional intestinal obstruction. According to the aganglionic segment length, patients could be classified as short-segment HSCR (S-HSCR), when aganglionosis extend as far as the rectosigmoid junction, and long-segment HSCR (L-HSCR), when it extends beyond it. HSCR presents an estimated incidence of 1/5000 live births with sex-dependent penetrance and male predominance of 4:1 [1,2]. It most commonly presents sporadically, although it can also be familial (up to 20% of the cases). The disease usually presents as isolated, though 30% of the cases are associated with chromosomal abnormalities, neurodevelopmental disorders and a variety of additional isolated anomalies and syndromes [2].HSCR has a complex genetic etiology with several genes being