Hyperphosphatemia

The most common cause of hyperphosphatemia, and most familiar to primary care physicians, is impaired renal function. It is also a characteristic of all forms of hypoparathyroid-ism, from the loss of inhibitory effect of PTH on phosphate reabsorption at the proximal renal tubule (Levine, 2006). High-phosphate formula provided to infants can result in hypocalcemia and tetany (Box 35-14).

Box 35-13 Causes of Functional Hypoparathyroidism

A.

Surgery

G.

Embryologic defects in parathyroid gland development

1. High-dose radiation (rarely)

2. Asparaginase

3. Ethiofos

1. DiGeorge syndrome (del 22q or TBX1 Mutation); DGS1; MIM 188400

2. DiGeorge syndrome (del 10p) DGS2; MIM 601362

3. Velocardiofacial syndrome (del 22q); MIM 192430

C.

Infiltrative processes

a. Kenny-Caffey/Sanjad-Sakati syndromes (TCBE, MIM 244460)

1. Iron deposition

H.

Defective synthesis of parathyroid hormone; MIM 168450

2. Copper deposition

1. Autosomal dominant mutation in prepro-PTH gene

3. Tumor or granuloma

2. Autosomal recessive mutation in prepro-PTH gene

1. Magnesium deficiency

2. Magnesium excess

3. Activating mutation of calcium-sensing receptor gene (MIM

I.

Metabolic defects and mitochondrial neuromyopathies

1. Kearn-Sayre syndrome

2. Person's syndrome

3. tRNA leu mutations

145980)

J.

Resistance to parathyroid hormone

4. Antibodies that activate the calcium-sensing receptor

1. Pseudohypoparathyroidism type 1a (MIM 103580)

5. Burn injury and upregulation of calcium-sensing receptor

2. Pseudohypoparathyroidism type 1b

6. Alcohol

3. Pseudohypoparathyroidism type 1c

7. Maternal hypercalcemia

4. Pseudohypoparathyroidism type 2

Autoimmune destruction of parathyroid glands

1. Autoimmune hypoparathyroidism

From Levine MA. Hypoparathyroidism and pseudohypoparathyroidism. In DeGroot LJ, Jameson JL (eds). Endocrinology, 5th ed, vol 2. Philadelphia, Elsevier-Saunders, 2006. PTH, Parathyroid hormone (parathormone).

2. Autoimmune polyglandular syndrome, type 1 (APECED, MIM

240300)

F.

Idiopathic hypoparathyroidism

1. Autosomal recessive (MIM 241400)

2. X-linked (MIM 307700)

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