Parathyroid tumors, resulting in primary hyperparathyroidism, are the most common feature of MEN1 and occur in ∼95% of MEN1 patients (Benson et al., 1987; Brandi et al., 2001; Calender et al., 1995; Marx et al., 1998; Trump et al., 1996). Here, MEN1 is linked to primary hyperparathyroidism.