Low bone mineral density and its influencing factors in spinal muscular atrophy without disease-modifying treatment: a single-centre cross-sectional study.

Background: Children with spinal muscular atrophy (SMA) are at risk of low bone mineral density (BMD) and bone fragility. This study aims to assess lumbar spine BMD measured by quantitative computed tomography (QCT) and investigate influencing factors of low BMD in children with SMA without disease-modifying treatment.

Methods: Demographic data, laboratory parameters, QCT data, and data on spinal radiographs were collected. A linear regression model was carried out to explore the correlations between BMD and its related factors.

Results: Sixty-six patients with SMA who had complete records between July 2017 and July 2023 were analyzed, with SMA with a mean age of 5.4 years (range, 2.4-9.7 years), including type 1 in 14, type 2 in 37, and type 3 in 15. 28.8% of patients (19/66) were diagnosed with low BMD (Z-scores ≤ - 2), and the mean BMD Z-scores on QCT was - 1.5 ± 1.0. In our model, BMD Z-scores was associated with age (β=-0.153, p = 0.001). SMA phenotype and serum bone metabolism markers, such as serum phosphorus (P), alkaline phosphatase (ALP) and 25-Hydroxyvitamin D (25-OH-D) levels did not independently predict low BMD. ROC analysis showed that the age ≥ 6.3 years predicts a Z-scores ≤ -2.0 with a sensitivity of 68.4% and a specificity of 68.1%.

Conclusions: Low BMD were highly prevalent in children with SMA without disease-modifying treatment in our centre. Regular monitoring of BMD is necessary for all types of SMA children, especially those aged ≥ 6.3 years.