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. The gene discussed is RET; the disease is hereditary pheochromocytoma-paraganglioma.