In mice, heterozygosity for two known mutant HSCR genes, RET+/− and Ednrbsl, or RET+/− and Ednrbs genes, had no intestinal aganglionosis, whereas RET+/− mice with the homozygous Ednrbs or heterozygous Ednrbs/Ednrbsl mutations showed megacolon [38], [40]. Here, EDNRB is linked to Aganglionic megacolon.