Parisi et al. hypothesized that in those cases in which X-linked hydrocephalus presents together with HSCR, either RET or another HSCR gene contributes to aganglionosis under the influence of a defective L1CAM gene, and L1CAM may act as an X linked modifier gene for the development of HSCR [8]. Here, RET is linked to Hirschsprung disease.