Diseases affecting the correct regulation of calcium and/or phosphate homeostasis, and, subsequently, bone mineralization, can be classified into: (1) disorders due to an excess or a deficiency of PTH secretion by the parathyroid glands (named hyperparathyroidism and hypoparathyroidism, respectively); (2) disorders caused by abnormal PTH receptor signaling (pseudohypoparathyroidism); (3) disorders due to altered vitamin D metabolism and activity (Table 4); and (4) congenital disorders of the phosphate homeostasis (Table 5). Here, PTH is linked to pseudohypoparathyroidism.