Accelerated bone turnover in pregnant women with McCune-Albright syndrome.

Bone turnover in pregnant women with McCune-Albright syndrome may be affected by both the syndrome and pregnancy. This study evaluated changes in biochemical bone turnover markers in pregnant women with the syndrome. Serum calcium, phosphorus, 1,25-dihydroxyvitamin D (1,25-(OH)2D), intact osteocalcin (I-OC) and alkaline phosphatase (ALP), and urinary pyridinoline (Pyr), deoxypyridinoline (D-Pyr) and hydroxyproline (HPR) were measured during pregnancy and postpartum in 2 women with McCune-Albright syndrome. Serum calcitonin (CT), and plasma intact parathyroid hormone (I-PTH) and parathyroid hormone-related protein (PTHrP) were also measured in 1 patient. Serum corrected Ca levels were normal or low-normal; phosphorus levels were normal, and 1,25-(OH)2D levels increased toward term and decreased thereafter, similar to normal pregnant women. Urinary Pyr, D-Pyr and HPR were elevated during pregnancy compared to normal pregnant women, peaked just after delivery, and decreased thereafter. Serum I-OC and ALP levels were high during pregnancy and postpartum. Intact PTH levels were increased during pregnancy and postpartum compared to normal pregnant women, whereas serum CT and PTHrP levels were not elevated. Both bone formation and absorption appear to be more enhanced during pregnancy and postpartum in women with McCune-Albright syndrome than in normal pregnant women. Additional or amplified cyclic AMP synthesis in bone cells through activation of the alpha subunit of G protein, independent of hormonal control, may explain the high local bone turnover.