Bone metabolism in patients with mucopolysaccharidosis type II

Objectives: To assess different parameters of bone metabolism in patients with mucopolysaccharidosis type II (MPS II) to better comprehend the mechanisms responsible for their skeletal pathology.

Material and methods: In MPS type II patients (n = 7, age 4–28 years, mean 11.6, median 7) bone metabolism was assessed using the following: a) parameters of calcium-phosphate metabolism (serum level of calcium, phosphorus, alkaline phosphatase (ALP), parathormone (PTH), and vitamin 25(OH)D), b) parameters of bone formation (osteocalcin) and resorption (B-crossLaps), c) bone mineral density (BMD) of the lumbar spine assessed by dual-energy X-ray absorptiometry (DXA), and d) radiographs of the skeletal system.

Results: All patients were normocalcemic, but the majority of them had abnormal serum levels of other parameters of calcium-phosphate metabolism such as: hypophosphatemia (4/7), decreased ALP (2/7), increased PTH (4/7), and vitamin 25(OH)D deficiency (6/7), which in 3 patients was associated with secondary hyperparathyroidism. Five patients presented increased levels of osteocalcin in the serum, and all the patients had high levels of β-CTx. Two adult patients had osteoporosis (T-scores –3.9 and –5.7), while in 3 pediatric patients the Z-score was within the normal range. Radiographs of bones revealed signs of dysostosis multiplex typical for MPS disease in all patients, and in adult patients they corresponded to BMD.

Conclusions: 1. MPS II patients have disturbed serum parameters of bone health and therefore may be at a higher risk for osteoporosis or osteomalacia. 2. Supplementation with vitamin D may be required in MPS patients.