Multiple endocrine neoplasia type 2A in a kindred with C634Y mutation.

Multiple endocrine neoplasia type 2A (MEN 2A) is most frequently caused by codon 634 activating mutations. Medullary thyroid carcinoma has occurred before the age of 2, with pheochromocytomas and primary hyperparathyroidism occurring later in childhood. We report cases of 4 siblings with C634Y-positive MEN 2A (all <11 years old): 3 with medullary thyroid carcinoma (1 had nodal metastasis, and another had a parathyroid adenoma) and 1 with C-cell hyperplasia.