MEN1 and neoplasm: More than 90% of tumors from MEN1 patients have loss of heterozygosity (LOH), and this has generally been taken as evidence that the MEN1 gene acts as a tumor-suppressor gene, consistent with Knudson’s two-hit hypothesis (Friedman et al., 1989; Larsson et al., 1988; Thakker et al., 1989).