A small proportion of these cases is caused by variants of other monogenic diseases – multiple endocrine neoplasia (MEN) type 1, 2A or 4 (MEN1, MEN2A, MEN4), hyperparathyroidism jaw tumor syndrome (HPT-JT) or familial hypocalciuric hypercalcemia – but additional genes are likely involved in the other cases (29). The gene discussed is CDKN1B; the disease is Hyperparathyroidism-jaw tumor syndrome.