CDKN1B and multiple endocrine neoplasia: MEN syndromes are now comprised of four subtypes: MEN 1, which results from a mutation in the MENIN gene, MEN 2 (formerly 2A) and MEN 3 (formerly 2B) resulting from mutations in the RET proto-oncogene, and MEN 4 resulting from mutations in the CDKN1B gene [1,2].