Pseudohypoparathyroidism is a condition caused by resistance to the parathyroid hormone. Patients have a low serum calcium and high phosphate, but the parathyroid hormone level (PTH) is appropriately high. Its pathogenesis has been linked to dysfunctional G Proteins.

Types

• Type 1a pseudohypoparathyroidism has a characteristic phenotypic appearance (Albright's hereditary osteodystrophy), including short fourth and fifth metacarpals and a rounded facies. It is most likely an autosomal dominant disorder.^[1]
• Type 1b pseudohypoparathyroidism lacks the physical appearance of type 1a, but is biochemically similar.^[2]
• Type 2 pseudohypoparathyroidism also lacks the physical appearance of type 1a.^[3] While biochemically similar, type 1 and 2 disease may be distinguished by the differing urinary excretion of cyclic AMP in response to exogenous PTH.

Related conditions

The term pseudopseudohypoparathyroidism is used to describe a condition where the individual has the phenotypic appearance of pseudohypoparathyroidism type 1a, but is biochemically normal.

Presentation

Patients may present with features of hypocalcaemia including; carpo-pedal spasm, tetany, muscle cramps and seizures. Type 1a Pseudohypoparathyroidism is clinically manifest by blunting of fourth and fifth metacarpals (The common mnemonic "knuckle knuckle dimple dimple" refers to the blunting of the fourth and fifth metacarpal bones), short stature, obesity, developmental delay.

Biochemical Findings

• hypocalcemia
• hyperphosphatemia
• elevated parathyroid hormone (hyperparathyroidism)

References

See also

• Hypoparathyroidism

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