All three pairs of identical twins exhibited varying clinical presentations, expressivity of MEN2-related MTC and/or pheochromocytoma, and associated biomarker levels.<h4>Conclusions</h4>Homozygous MEN2A accelerates MTC onset and increases metastasis risk, but there is no evidence of association with the development of pheochromocytoma. This evidence concerns the gene RET and medullary thyroid gland carcinoma.