Here is something I read on the Johns Hopkins HD research page.
Is there another syndrome caused by changes in the RET gene?
Multiple Endocrine Neoplasia Type 2 (MEN2) is an inherited cancer syndrome. People who have MEN2 are at increased risk to get medullary thyroid cancer (MTC), pheochromocytoma (tumor of the adrenal gland), and parathyroid tumors. MEN2 includes 3 slightly different syndromes, including MEN2A, MEN2B, and FMTC (familial medullary thyroid cancer). Like Hirschsprung disease, it is caused by mutations in the RET gene; however, a different type of mutation usually causes MEN2 and the mutations occur in a very specific part of the gene. Individuals have been described who have both Hirschsprung disease and an MEN2-associated RET mutation and cancer. A person with Hirschsprung disease and a personal or family history of endocrine tumors should see a doctor for diagnosis, testing options, and possible monitoring.
*****In 2009, a taskforce of the American Thyroid Association published a recommendation that testing for MEN-associated RET mutations be considered in all patients with Hirschsprung disease because if a mutation that increases cancer risk is found lifesaving preventive and screening options are available. **
** this is the line I found most interesting.