Hypocalcemia: Reduction of the blood calcium below normal. Manifestations include hyperactive deep tendon reflexes, Chvostek's sign, muscle and abdominal cramps, and carpopedal spasm. (Dorland, 27th ed)Hypoparathyroidism: A condition caused by a deficiency of PARATHYROID HORMONE (or PTH). It is characterized by HYPOCALCEMIA and hyperphosphatemia. Hypocalcemia leads to TETANY. The acquired form is due to removal or injuries to the PARATHYROID GLANDS. The congenital form is due to mutations of genes, such as TBX1; (see DIGEORGE SYNDROME); CASR encoding CALCIUM-SENSING RECEPTOR; or PTH encoding parathyroid hormone.Parathyroid Hormone: A polypeptide hormone (84 amino acid residues) secreted by the PARATHYROID GLANDS which performs the essential role of maintaining intracellular CALCIUM levels in the body. Parathyroid hormone increases intracellular calcium by promoting the release of CALCIUM from BONE, increases the intestinal absorption of calcium, increases the renal tubular reabsorption of calcium, and increases the renal excretion of phosphates.Magnesium Deficiency: A nutritional condition produced by a deficiency of magnesium in the diet, characterized by anorexia, nausea, vomiting, lethargy, and weakness. Symptoms are paresthesias, muscle cramps, irritability, decreased attention span, and mental confusion, possibly requiring months to appear. Deficiency of body magnesium can exist even when serum values are normal. In addition, magnesium deficiency may be organ-selective, since certain tissues become deficient before others. (Harrison's Principles of Internal Medicine, 12th ed, p1936)Calcium Gluconate: The calcium salt of gluconic acid. The compound has a variety of uses, including its use as a calcium replenisher in hypocalcemic states.Thyroidectomy: Surgical removal of the thyroid gland. (Dorland, 28th ed)Parathyroid Glands: Two pairs of small oval-shaped glands located in the front and the base of the NECK and adjacent to the two lobes of THYROID GLAND. They secrete PARATHYROID HORMONE that regulates the balance of CALCIUM; PHOSPHORUS; and MAGNESIUM in the body.Pseudohypoparathyroidism: A hereditary syndrome clinically similar to HYPOPARATHYROIDISM. It is characterized by HYPOCALCEMIA; HYPERPHOSPHATEMIA; and associated skeletal development impairment and caused by failure of response to PARATHYROID HORMONE rather than deficiencies. A severe form with resistance to multiple hormones is referred to as Type 1a and is associated with maternal mutant allele of the ALPHA CHAIN OF STIMULATORY G PROTEIN.Hypercalcemia: Abnormally high level of calcium in the blood.Receptors, Calcium-Sensing: A class of G-protein-coupled receptors that react to varying extracellular CALCIUM levels. Calcium-sensing receptors in the PARATHYROID GLANDS play an important role in the maintenance of calcium HOMEOSTASIS by regulating the release of PARATHYROID HORMONE. They differ from INTRACELLULAR CALCIUM-SENSING PROTEINS which sense intracellular calcium levels.Parathyroidectomy: Excision of one or more of the parathyroid glands.Calcium: A basic element found in nearly all organized tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.22q11 Deletion Syndrome: Condition with a variable constellation of phenotypes due to deletion polymorphisms at chromosome location 22q11. It encompasses several syndromes with overlapping abnormalities including the DIGEORGE SYNDROME, VELOCARDIOFACIAL SYNDROME, and CONOTRUNCAL AMOMALY FACE SYNDROME. In addition, variable developmental problems and schizoid features are also associated with this syndrome. (From BMC Med Genet. 2009 Feb 25;10:16) Not all deletions at 22q11 result in the 22q11deletion syndrome.Hyperparathyroidism, Secondary: Abnormally elevated PARATHYROID HORMONE secretion as a response to HYPOCALCEMIA. It is caused by chronic KIDNEY FAILURE or other abnormalities in the controls of bone and mineral metabolism, leading to various BONE DISEASES, such as RENAL OSTEODYSTROPHY.Phosphorus: A non-metal element that has the atomic symbol P, atomic number 15, and atomic weight 31. It is an essential element that takes part in a broad variety of biochemical reactions.Rickets: Disorders caused by interruption of BONE MINERALIZATION manifesting as OSTEOMALACIA in adults and characteristic deformities in infancy and childhood due to disturbances in normal BONE FORMATION. The mineralization process may be interrupted by disruption of VITAMIN D; PHOSPHORUS; or CALCIUM homeostasis, resulting from dietary deficiencies, or acquired, or inherited metabolic, or hormonal disturbances.Hyperparathyroidism: A condition of abnormally elevated output of PARATHYROID HORMONE (or PTH) triggering responses that increase blood CALCIUM. It is characterized by HYPERCALCEMIA and BONE RESORPTION, eventually leading to bone diseases. PRIMARY HYPERPARATHYROIDISM is caused by parathyroid HYPERPLASIA or PARATHYROID NEOPLASMS. SECONDARY HYPERPARATHYROIDISM is increased PTH secretion in response to HYPOCALCEMIA, usually caused by chronic KIDNEY DISEASES.Magnesium: A metallic element that has the atomic symbol Mg, atomic number 12, and atomic weight 24.31. It is important for the activity of many enzymes, especially those involved in OXIDATIVE PHOSPHORYLATION.Calcitriol: The physiologically active form of vitamin D. It is formed primarily in the kidney by enzymatic hydroxylation of 25-hydroxycholecalciferol (CALCIFEDIOL). Its production is stimulated by low blood calcium levels and parathyroid hormone. Calcitriol increases intestinal absorption of calcium and phosphorus, and in concert with parathyroid hormone increases bone resorption.Vitamin D: A vitamin that includes both CHOLECALCIFEROLS and ERGOCALCIFEROLS, which have the common effect of preventing or curing RICKETS in animals. It can also be viewed as a hormone since it can be formed in SKIN by action of ULTRAVIOLET RAYS upon the precursors, 7-dehydrocholesterol and ERGOSTEROL, and acts on VITAMIN D RECEPTORS to regulate CALCIUM in opposition to PARATHYROID HORMONE.DiGeorge Syndrome: Congenital syndrome characterized by a wide spectrum of characteristics including the absence of the THYMUS and PARATHYROID GLANDS resulting in T-cell immunodeficiency, HYPOCALCEMIA, defects in the outflow tract of the heart, and craniofacial anomalies.Hyperparathyroidism, Primary: A condition of abnormally elevated output of PARATHYROID HORMONE due to parathyroid HYPERPLASIA or PARATHYROID NEOPLASMS. It is characterized by the combination of HYPERCALCEMIA, phosphaturia, elevated renal 1,25-DIHYDROXYVITAMIN D3 synthesis, and increased BONE RESORPTION.Phosphates: Inorganic salts of phosphoric acid.Calcium Metabolism Disorders: Disorders in the processing of calcium in the body: its absorption, transport, storage, and utilization.Parathyroid Diseases: Pathological processes of the PARATHYROID GLANDS. They usually manifest as hypersecretion or hyposecretion of PARATHYROID HORMONE that regulates the balance of CALCIUM; PHOSPHORUS; and MAGNESIUM in the body.Tetany: A disorder characterized by muscle twitches, cramps, and carpopedal spasm, and when severe, laryngospasm and seizures. This condition is associated with unstable depolarization of axonal membranes, primarily in the peripheral nervous system. Tetany usually results from HYPOCALCEMIA or reduced serum levels of MAGNESIUM that may be associated with HYPERVENTILATION; HYPOPARATHYROIDISM; RICKETS; UREMIA; or other conditions. (From Adams et al., Principles of Neurology, 6th ed, p1490)Vitamin D Deficiency: A nutritional condition produced by a deficiency of VITAMIN D in the diet, insufficient production of vitamin D in the skin, inadequate absorption of vitamin D from the diet, or abnormal conversion of vitamin D to its bioactive metabolites. It is manifested clinically as RICKETS in children and OSTEOMALACIA in adults. (From Cecil Textbook of Medicine, 19th ed, p1406)Calcitonin: A peptide hormone that lowers calcium concentration in the blood. In humans, it is released by thyroid cells and acts to decrease the formation and absorptive activity of osteoclasts. Its role in regulating plasma calcium is much greater in children and in certain diseases than in normal adults.Thyroid Diseases: Pathological processes involving the THYROID GLAND.Calcium, Dietary: Calcium compounds used as food supplements or in food to supply the body with calcium. Dietary calcium is needed during growth for bone development and for maintenance of skeletal integrity later in life to prevent osteoporosis.Graves Disease: A common form of hyperthyroidism with a diffuse hyperplastic GOITER. It is an autoimmune disorder that produces antibodies against the THYROID STIMULATING HORMONE RECEPTOR. These autoantibodies activate the TSH receptor, thereby stimulating the THYROID GLAND and hypersecretion of THYROID HORMONES. These autoantibodies can also affect the eyes (GRAVES OPHTHALMOPATHY) and the skin (Graves dermopathy).Diphosphonates: Organic compounds which contain P-C-P bonds, where P stands for phosphonates or phosphonic acids. These compounds affect calcium metabolism. They inhibit ectopic calcification and slow down bone resorption and bone turnover. Technetium complexes of diphosphonates have been used successfully as bone scanning agents.Hypophosphatemia: A condition of an abnormally low level of PHOSPHATES in the blood.Magnesium Sulfate: A small colorless crystal used as an anticonvulsant, a cathartic, and an electrolyte replenisher in the treatment of pre-eclampsia and eclampsia. It causes direct inhibition of action potentials in myometrial muscle cells. Excitation and contraction are uncoupled, which decreases the frequency and force of contractions. (From AMA Drug Evaluations Annual, 1992, p1083)Renal Osteodystrophy: Decalcification of bone or abnormal bone development due to chronic KIDNEY DISEASES, in which 1,25-DIHYDROXYVITAMIN D3 synthesis by the kidneys is impaired, leading to reduced negative feedback on PARATHYROID HORMONE. The resulting SECONDARY HYPERPARATHYROIDISM eventually leads to bone disorders.Osteomalacia: Disorder caused by an interruption of the mineralization of organic bone matrix leading to bone softening, bone pain, and weakness. It is the adult form of rickets resulting from disruption of VITAMIN D; PHOSPHORUS; or CALCIUM homeostasis.Parathyroid Neoplasms: Tumors or cancer of the PARATHYROID GLANDS.Bone Density Conservation Agents: Agents that inhibit BONE RESORPTION and/or favor BONE MINERALIZATION and BONE REGENERATION. They are used to heal BONE FRACTURES and to treat METABOLIC BONE DISEASES such as OSTEOPOROSIS.Hyperphosphatemia: A condition of abnormally high level of PHOSPHATES in the blood, usually significantly above the normal range of 0.84-1.58 mmol per liter of serum.Calcium Chloride: A salt used to replenish calcium levels, as an acid-producing diuretic, and as an antidote for magnesium poisoning.Syntaxin 16: A ubiquitously expressed member of the syntaxin subfamily of SNARE proteins that localizes to the GOLGI APPARATUS.Chelation Therapy: Therapy of heavy metal poisoning using agents which sequester the metal from organs or tissues and bind it firmly within the ring structure of a new compound which can be eliminated from the body.