MEN1 and hyperparathyroidism: MEN1 penetrance is high, with more than 95% ofMEN1 mutation carriers having biochemical evidence of MEN1—generally represented by mono- or pluri-hormones over secretion—with 100% presenting with hyperparathyroidism by 50 years of age and approximately 80% of patients presenting clinical signs by the fifth decade of life12 (Table 1).