Genetic variation: Currently there are 10 different genes identified (RET, GDNF, NTN, EDNRB, ET3, ECE-1, SOX10, ZFHX1B, PHOX2B, NGR1) in individuals affected with either isolated or syndromic Hirschsprung disease. The RET gene plays a critical role in ENS development and mutations in the RET gene have been found in 7-35% of sporadic cases and approximately 50% of familial cases. EDNRB and ET3 each account for approximately 5% of patients with HD and also are responsible for Shah-Waardenberg Syndrome. Mutations in each of the remaining 7 genes have been found in a small number of isolated and syndromic HD patients[8].