MEN1 mutations have been reported in 42 families with isolated hyperparathyroidism (FIHP) (Hannan et al., 2008; Lemos and Thakker, 2008), and 38% of these are missense mutations, and fewer than 31% are nonsense or frame-shift mutations, which would result in a truncated and likely inactivated protein. This evidence concerns the gene MEN1 and familial isolated hyperparathyroidism.