While loss-of-function mutations in calcium-signaling-related genes, such as CASR, GNA11, and AP2S1, are associated with familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT), these mutations are not associated with parathyroid neoplasms [17,18,19,20]. Here, AP2S1 is linked to neonatal severe primary hyperparathyroidism.