Tumor development is caused by biallelic inactivation of the MEN1 tumor suppressor gene, with the first gene copy being inactivated at birth by a heterozygote germinal mutation, inherited by the affected parent or, rarely, developed at the first stage of embryonic development, and the second wild type copy lost at parathyroid somatic level prevalently by loss of heterozygosity (LOH) at the 11q13 locus or, more rarely, by loss-of-function point mutations or small indels. Here, MEN1 is linked to neoplasm.