Certain mutations in KLKB1, mutated in one of five CT-pNENs, cause prekallikrein deficiency (56), and KLKB1 was mutually exclusive with ATRX, DAXX, and MEN1 of pancreatic neuroendocrine tumors (PanNets) (57, 58). Here, MEN1 is linked to prekallikrein deficiency.