Parathyroid disorders and diseases altering calcium metabolism

The control of body calcium involves a balance—chiefly under the control of parathyroid hormone (PTH)—between the amounts that are absorbed from the gut, deposited into bone and into cells, and excreted from the kidney. Abnormalities of the parathyroid glands themselves will cause derangements of calcium homeostasis and several clinical disorders. PTH oversecretion due to parathyroid tumours, which affect 3 in 1000 of the population, is a major cause of hypercalcaemia which may be associated with kidney stones, osteoporosis, and peptic ulcers. PTH deficiency, which results in hypocalcaemia and occurs in 1 in 4000 live births, may be associated with epilepsy, tetany, cataracts, skeletal malformations, and abnormal dentition. This chapter will review the physiological and biochemical mechanisms underlying extracellular calcium homeostasis, the clinical features of hypercalcaemia and hypocalcaemia, the clinical disorders associated with abnormal calcium homeostasis and their management, and the genetic basis for disorders of calcium metabolism.