Familial associations in medullary thyroid carcinoma with Hirschsprung disease: the role of the RET-C620 “Janus” genetic variation

IntroductionHirschsprung disease (HSCR) is associated with the later development of multiple endocrine neoplasia (MEN2), because RET gene variations are associated with both conditions. Specifically, HSCR-MEN2 cosegregation mostly relates to the cysteine-rich area at the RET-620 (the “Janus gene”).AimThe aim of this study was to explore the clinical and genetic associations of HSCR-MEN2 in a cohort of HSCR patients.MethodsRET gene variation was evaluated by heteroduplex single-strand conformational polymorphism analysis and validated with automated sequencing techniques in HSCR patients (including 18 kindreds). Those with RET C620 variations were subjected to familial evaluation for coexisting HSCR-MEN2.ResultsA cohort of 118 patients with HSCR (n = 89) or medullary thyroid carcinoma (n = 29) were studied, including 3 families where a RET-620 point mutation was identified. No C618, C609, or C611 variations were detected. In 1 remarkable 6-generational family (family 3), HSCR in early generations seemed to be later replaced by MEN2A. In the other 2 families with total colonic aganglionosis, a relative with a medullary thyroid carcinoma was identified.ConclusionGene mutation in the RET-620 position carries significant risk and may be part of a targeted investigation of high-risk areas in HSCR. We propose an alternative hypothesis of endoplasmic reticulum control to explain the changing phenotypic expression.