RET and Hirschsprung disease: The MEN2 syndromes are associated with RET proto-oncogene mutation and have predisposition for tumours involving two or more endocrine glands, including MTC for 95% of carriers.4 The RET proto-oncogene is also the major gene involved in Hirschsprung’s disease, with loss-of-function mutations identified in over 70% of cases and an association with long segments of aganglionic bowel.