In the remaining cases (20-25%), it is an autosomal dominant hereditary disease with a high degree of penetrance and variability of expression, which may be part of two distinct clinical syndromes depending on the organs involved, i.e., type 2A multiple endocrine neoplasia (MEN2A) or type 2B multiple endocrine neoplasia (MEN2B). This evidence concerns the gene RET and multiple endocrine neoplasia type 2A.