Genotype/phenotype correlations in multiple endocrine neoplasia type 2

Multiple endocrine neoplasia type 2 (MEN 2) is a rare hereditary endocrine tumor syndrome caused by mutations in the rearranged during transfection (RET) gene. MEN 2 is divided into two main entities, MEN 2A and MEN 2B, both of which present with medullary thyroid cancer (MTC) in approximately 100% of cases and pheochromocytoma in 50% of cases. Specific RET mutations are associated with a risk of early onset of MTC, from 1 year of age (highest risk) to 5 years of age (high risk). This risk defines the optimal timing for thyroidectomy, ideally at an age when the disease has not spread. This is the most important genotype-phenotype correlation observed in MEN 2. Specific RET mutations also define the penetrance of pheochromocytoma. However, despite the presence of these highest/high-risk variants, some patients unexpectedly present with non-aggressive MTC or never present with pheochromocytoma, suggesting that factors other than the major RET variant may modify the natural history and genotype-phenotype correlations. Improving our understanding of the genotype-phenotype correlations would allow individualizing the management and follow-up of patients with MEN 2. The aim of this brief review is to discuss the main genotype-phenotype correlations in MEN 2 and the potential factors that might influence these correlations.