A genetic background is found in 10–30% of juvenile cases, typically involving deletions/duplications or pathogenic variants of the MEN1, which underlines multiple endocrine neoplasia type 1 syndrome (MEN1), CDC73 (also known as HRPT2; its germline pathogenic variant causes hyperparathyroidism (jaw tumor syndrome)), CDKN1B, RET (MEN2), AIP, CDKN1B, and CASR (calcium-sensing receptor) genes, requiring differential diagnosis of familial hypocalciuric hypercalcemia, which might be complicated by severe neonatal PHP with homozygote status [16,17,18,19]. This evidence concerns the gene CASR and hyperparathyroidism.