The age at diagnosis of PHPT in our patient (41 years), which was similar to those previously reported for other MEN4 cases carrying nonsense or frameshift mutations of CDKN1B (W76X and K25fs), was older than the mean age of diagnosis of PHPT in patients with MEN1 syndrome (25 years) (30), but younger than that of MEN4 patients harboring missense (56 years) and 5′UTR mutations in CDKN1B (67 years) (31). Here, CDKN1B is linked to multiple endocrine neoplasia type 1.