Assessment of bone health and bone mineral density in patients with mucopolysaccharidosis receiving enzyme replacement therapy

Abstract

BACKGROUND: Most patients with mucopolysaccharidosis (MPS) experience skeletal involvement due to impaired bone remodeling, glycosaminoglycan (GAG) accumulation, reduced mobility, and nutritional deficiencies. These factors may predispose to low bone mass and increased fracture risk. This study assessed bone mineral density (BMD) using height-adjusted dual-energy X-ray absorptiometry (DXA) in pediatric MPS patients receiving enzyme replacement therapy (ERT) and examined its associations with clinical, functional, and biochemical parameters. METHODS: This cross-sectional study included 29 children with biochemically and/or genetically confirmed MPS receiving ERT at Tanta University Hospital. Children under 5 years and ERT-naïve patients were excluded. BMD was measured at the lumbar spine (L1-L4) and femoral neck using DXA and adjusted for height-for-age z-score (HAZ). Clinical data, Katz Activities of Daily Living (ADL) score, anthropometry, and biochemical markers of bone metabolism were recorded. Statistical analyses included the Shapiro-Wilk test, Pearson correlation, and two-tailed t-test (p < 0.05). RESULTS: The cohort included 29 patients (19 males, 10 females; mean age 9.79 ± 3.85 years): 13 with MPS IVA, 11 with MPS I, 3 with MPS II, and 2 with MPS VI. Mean HAZ-adjusted BMD z-scores were - 1.84 ± 1.38 (right femur), - 2.07 ± 1.22 (left femur), and - 3.00 ± 1.49 (lumbar spine). Low bone mass for age (HAZ-adjusted z ≤ - 2) was present in 20/29 (68.9%) patients, predominantly affecting the spine. Vitamin D insufficiency/deficiency was observed in 75.9% of patients. Katz ADL score correlated strongly with BMD at all sites, particularly the lumbar spine (r = 0.88, p < 0.001). Total calcium and vitamin D levels showed positive correlations with BMD. Patients with cardiac involvement had significantly lower BMI than those without cardiac disease (p < 0.001). CONCLUSIONS: Pediatric patients with MPS receiving ERT show a high prevalence of low bone mass for age, driven by a multifactorial interaction between impaired mobility, nutritional deficiencies, and intrinsic skeletal pathology. Routine height-adjusted DXA monitoring, early physiotherapy, and proactive vitamin D and calcium supplementation should be integrated into comprehensive MPS care.