The serum bone Gla protein (BGP) level was measured in patients with idiopathic hypoparathyroidism, and primary hyperparathyroidism, and normal volunteers. The mean serum BGP level was 4.5±0.20μg/l in 40 normal volunteers. It was significantly lower in 12 patients with idiopathic hypoparathyroidism (1.6±0.21μg/l, p<0.001) and significantly higher in 33 patients with primary hyperparathyroidism (13.0±1.3μg/1, p<0.001).
When a single intravenous injection of 30μg of human PTH 1-34 was administered to the patients with idiopathic hypoparathyroidism, there was no significant change in serum BGP within the next 24 hours. Following a therapeutic oral dose of alfacalcidol, serum BGP was appreciably increased (p<0.001) from the preadministration value of 1.6±0.21μg/l to 3.9±0.34μg/l.
In patients with primary hyperparathyroidism, the surgical excision of parathyroid adenoma led to a sharp decrease in serum PTH but a gradual decrease in serum BGP. The latter approximately paralleled the decline in serum alkaline phosphatase.
Thus, serum BGP is a marker that reflects bone turnover status in parathyroid disease. It appears that the active form of vitamin D directly increases the secretion of BGP in existing osteoblasts and PTH mainly affects serum BGP to stimulate the bone remodeling cycles with its long term effect.