However, in 5% to 25% of patients with a MEN-1 phenotype, genetic testing is negative for MEN1 mutations, which may be explained by mutations in as yet unidentified genes or may represent phenocopies (clinical phenotypes that mimic those associated with known genetic mutations, but which occur without the expected genotype) (2, 4, 5). Here, MEN1 is linked to multiple endocrine neoplasia type 1.