RET and multiple endocrine neoplasia type 2B: MEN2A subtype is caused by mutations in exons 10 and 11 of the gene, which specifically encodes the cysteine-rich extracellular domains of the RET protein, while mutations responsible for the MEN2B clinical subtype, which does not manifest any parathyroid tumorigenesis, are located in exons 15 and 16 and affect the tyrosine kinase intracellular domain of the RET protein.