pseudohypoparathyroidism

A disorder resembling hypoparathyroidism, with high serum phosphate and low calcium levels but with normal or elevated serum parathyroid hormone levels; the defect is due to lack of end-organ responsiveness to parathyroid hormone. There are two types: type I shows lack of renal tubular response to exogenous parathyroid hormone with increase in urinary cAMP, type Is has type I skeletal defects (SYN Albright hereditary osteodystrophy), and type II is associated with a defect at a locus after cAMP production. X-linked dominant inheritance caused by mutation in the gene encoding guanine nucleotide-binding protein α-stimulating activity polypeptide 1 (GNAS1), which regulates adenyl cyclase on chromosome 20q. Cf.:thyrotropin resistance.

- p. type Ia p. believed to be due to a defect in the G protein associated with adenylate cyclase (probably autosomal dominant).

- p. type Ib p. due to a defect in the adenylate cyclase complex.

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pseu·do·hy·po·para·thy·roid·ism -.hī-pō-.par-ə-'thī-.rȯid-.iz-əm n a usu. inherited disorder that clinically resembles hypoparathyroidism but results from the body's inability to respond normally to parathyroid hormone rather than from a deficiency of the hormone itself

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n.

a syndrome of mental retardation, restricted growth, and bony abnormalities due to a genetic defect that causes lack of response to the hormone secreted by the parathyroid glands. Treatment with calcium and vitamin D can reverse most of the features. See also Albright's hereditary osteodystrophy.

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pseu·do·hy·po·para·thy·roi·dism (PHP) (soo″do-hi″po-par″ə-thiґroi-diz″əm) a hereditary condition clinically resembling hypoparathyroidism, but caused by inability to respond to, rather than deficiency of, parathyroid hormone. The major cause is defective G proteins required for signal transduction; in some cases, there is an associated inability to respond to other hormones that require the same G protein types. It is characterized by hypocalcemia and hyperphosphatemia, and is commonly associated with short stature, obesity, short metacarpals, and ectopic calcification.

Pseudohypoparathyroidism with shortening of the metacarpals of the middle and ring fingers (posteroanterior view).