Cinacalcet as adjunctive therapy in pseudohypoparathyroidism type 1b

In patients with pseudohypoparathyroidism type 1b (PHP1b) due to a tissue-specific imprinting defect in the G-protein α-subunit, skeletal disorders can arise from the bones being sensitive to parathyroid hormone (PTH) while the kidneys remain resistant to this hormone.

We report a 4.8-year-old girl with PHP1b who presented with an abnormal gait, severe skeletal changes and elevated levels of serum PTH (2844 pg/ml), phosphate (7.2 mg/dl) and bone turnover markers. Traditional treatment with calcium and calcitriol failed to suppress PTH secretion, which was still elevated at 2877 pg/ml after 14 months of therapy, nor did it correct the other clinical, biochemical and radiographic abnormalities. The addition of cinacalcet to the treatment regimen over the subsequent 32 months resulted in normalization of serum PTH (58 ng/ml), phosphate (4.9 mg/dl) and bone turnover markers, and resolution of the radiographic changes, with no adverse effects noted.

Due to its ease of administration, we recommend the addition of cinacalcet into the armamentarium of medications available to treat children with PHP1b.