CDKN1B and multiple endocrine neoplasia type 1: In MEN1 syndrome, tumours occur in the parathyroid glands, pancreas, and pituitary and less commonly elsewhere, whereas in the very rare MEN4 syndrome a broader spectrum of organ pathology including PHPT, pituitary, and pancreatic tumours occurs, with neuroendocrine tumours also described at a variety of other sites (e.g., cervix, bronchus, and stomach) [5–9]. CDKN1B encodes p27(kip1), a cyclin-dependent kinase 2 inhibitor involved with the control of the cell cycle at G1 [10].