Synonyms: pseudohypoparathyroidism Ia, pseudo-pseudohypoparathyroidism
Inheritance: autosomal dominant
Molecular defect: defect in the G protein located on cell membranes, associated with a mutation in the GNAS1 gene in q13.11 region on chromosome 20. This protein is found on renal tubular cells, fibroblasts, platelets and erythrocytes.
Clinical findings:
(1) short stature
(2) obesity
(3) round face
(4) short neck
(5) low nasal bridge
(6) mental retardation
(7) cataracts
(8) calcifications in soft tissues
(9) shortening of metacarpal and metatarsal bones (usually the 4th and 5th)
(10) cone-shaped epiphysis
(11) low bone density with osteoporosis (due to effect of parathyroid hormone on osteoclasts)
Laboratory findings in AHO (pseudohypoparathryoidism Ia):
(1) hypocalcemia
(2) hyperphosphatemia
(3) elevated serum parathyroid hormone (PTH) concentration
(4) failure of urine cAMP to increase after infusion of PTH (renal PTH "resistance")
(5) increased urine hydroxyproline (or other markers of bone resorption)
Laboratory findings in pseudo-pseudohypoparathyroidism:
(1) normal serum calcium
(2) normal increase in urine cAMP after infusion of PTH
