pseudohypoparathyroidism
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Introduction
Congenital & hereditary disorder of PTH resistance.
Etiology
resistance to PTH (generally partial resistance)
Pathology
- parathyroid hyperplasia
- diminished urinary cAMP response to PTH
Genetics
- X-linked form
- autosomal form
- defective allele for Gs-alpha, GNAS (type 1A)
- defects in methylation of GNAS/GNAS1 gene; normal activity of the product of GNAS (type 1B)
Clinical manifestations
- symptoms of hypothyroidism
- developmental & skeletal abnormalities
- most patients show characteristic phenotype of Albright's hereditary osteodystrophy (also involves GNAS)
- type 1B lacks developmental defects characteristic of Albright's hereditary osteodystrophy
Laboratory
- serum PTH: elevated
- serum magnesium: hypomagnesemia
- serum calcium: diminished
- serum phosphate: elevated
- serum 25-OH vitamin D: low (vitamin D deficiency)
- renal function tests (chronic renal failure)
Management
- treat as hypoparathyroidism except that the doses of vitamin D & calcium are usually lower than those with true hypopara-thyroidism
More general terms
More specific terms
Additional terms
- Albright's hereditary osteodystrophy (AHO)
- GTP-binding regulatory protein Gs alpha (adenylate cyclase-stimulating, GNAS GNAS1, GSP)
- hyperparathyroidism
- hypomagnesemia
- hypoparathyroidism
References
- ↑ Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998
- ↑ Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 2244-45
- ↑ Harrison's Principles of Internal Medicine, 13th ed. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 1258