In rare MEN1 and MEN4-like patients with negative genetic results, other CDKIs pathological variants (p15 [CDKN2B, 1%], p18 [CDKN2C, 0.5%], p21 [CDKN1A, 0.5%]) should be considered [114], as well as CDC73 gene mutation [81,115,116] (responsible for hyperparathyroidism-jaw tumour syndrome) and CaSR mutation [115,116] (causing familial hypocalciuric hypercalcemia). Here, CDKN1A is linked to hyperparathyroidism.