Germline mutations in the MEN1 gene result in structural changes in menin, which lead to multiple endocrine neoplasia type 1 (the MEN1 syndrome), an autosomal dominant hereditary disease characterized by high penetrance (reaching 100% with age) and associated with the development of over 20 types of endocrine and non-endocrine tumors [203]. This evidence concerns the gene MEN1 and multiple endocrine neoplasia type 1.