MEN2 syndrome, due to mutations in the RET proto-oncogene (RET), presents a well-described genotype–phenotype association, so genetic testing is pivotal for MEN2 subtype diagnosis, MTC risk estimation, adequate management and the monitoring and follow-up of patients in order to improve outcomes for affected individuals [5,6,7,8]. The gene discussed is RET; the disease is medullary thyroid gland carcinoma.