Two Cases of Pseudohypoparathyroidism Type Ia in Duozygotic Twins with Different Phenotypes

Pseudohypoparathyroidism (PHP) type Ia is characterized by hypocalcemia due to PTH resistance and by features of Albright's hereditary osteodystrophy, including short stature, obesity, subcutaneous calcification and brachydactyly. A wide variety of clinical and biochemical manifestations have been reported. We report two cases of PHP type Ia in duozygotic twins with different phenotypes. The proband was a 10-yr-old girl. She showed subcutaneous ossification, shortening of the metacarpal bone, short stature, obesity and round face. She had normocalcemia (8.9 mg/dl), high-normal phosphate (5.0 mg/dl) and increased levels of serum intact PTH (152 pg/ml) and TSH (9.17 μIU/ml) levels. Her twin younger brother had atypical Albright's hereditary osteodystrophy with only mild obesity and subcutaneous calcifications, but he showed a low level of serum calcium (7.0 mg/dl) and high levels of serum phosphate (7.6 mg/dl), intact PTH (377 pg/ml) and TSH (6.9 μIU/ml). We diagnosed them as having PHP type Ia on the basis of clinical and biochemical findings, Ellsworth-Howard test and family history. There is considerable variability in clinical and biochemical features of PHP type Ia even among affected duozygotic twins. The differences of intrauterine environment and growth history cannot account for the variable phenotypes of PHP type Ia. Even if a patient shows no AHO features, examination of all family members should be undertaken.