Occurrence of MEN 2a in familial Hirschsprung's disease: a new indication for genetic testing of the RET proto-oncogene.

PURPOSE: The association of the rare hereditary cancer syndrome, multiple endocrine neoplasia type 2a (MEN 2a) with Hirschsprung's disease, both linked to germline mutations in the RET proto-oncogene, has been reported recently. With the widespread availability of genetic screening for MEN 2a, it is necessary to define the indications for genetic testing of MEN 2a and population subgroups at high risk for inheriting the disease. The purpose of this study was to assess the prevalence of Hirschsprung's disease in MEN 2a and investigate the value of genetic analysis for MEN 2a in children with familial Hirschsprung's disease.
METHODS: The ethnically diverse study group consisted of unselected consecutive patients (n=426) at risk for hereditary medullary thyroid cancer (MTC) referred to a single laboratory for genetic testing. Analysis used genomic DNA and a polymerase chain reaction-based heteroduplex mutation detection strategy for exons 10, 11, 13, and 14 of the RET proto-oncogene followed by direct DNA sequencing. Significance of RET genotype-phenotype correlation was determined by Fisher's two-tailed Exact test and a 2 x 2 contingency table.
RESULTS: Thirty-six distinctly new MEN 2a kindreds were identified. Hirschsprung's disease cosegregated among siblings with MEN 2a in 15 patients from 6 of the 36 (17%) families. The extent of aganglionosis in the 15 patients ranged from midrectum to duodenum. Of the 15 patients with Hirschsprung's disease, 10 (six boys, four girls) underwent thyroidectomy for MTC (n=5) or C-cell hyperplasia (n = 5) at ages 2 to 47 years (mean, 15.6 years), and the remaining five patients died in childhood of complications related to the aganglionosis. In retrospect, Hirschsprung's disease was the presenting feature of MEN 2a in five of the six families rather than MTC or pheochromocytoma. In all six MEN 2a families expressing Hirschsprung's disease, the RET mutation predisposing to the combined phenotype occurred in exon 10 at codons 609 (n=2), 618 (n=3), or 620 (n = 1). By contrast, the MEN 2a with Hirschsprung's phenotype was not found in any of the 22 families with a RETexon 11, 13, or 14 mutation (P=.0007).
CONCLUSIONS: The authors conclude that Hirschsprung's disease is a phenotypic marker for MEN 2a and possibly more common than originally appreciated. The expression of Hirschsprung's disease with MEN 2a may be uniquely linked to RETexon 10 mutations. The authors recommend that (1) patients affected with MEN 2a may be counseled regarding the potential risk of Hirschsprung's disease in offspring and (2) a family history of MTC be explored in children with familial Hirschsprung's disease and genetic screening for MEN 2a be considered.