Prevalence of Hypovitaminosis D and Its Association with Motor Impairment in Spinal Muscular Atrophy

Background/Objectives: In recent years, the role of vitamin D in the etiology of central and peripheral neurological diseases has been widely investigated, and evidence suggests benefits of vitamin D replacement therapy. However, few studies have evaluated the relationship between serum vitamin D levels and patients with spinal muscular atrophy (SMA). Therefore, this study aimed to analyze serum vitamin D levels in patients with SMA and their relationship with disease type, degree of motor impairment, and the presence of musculoskeletal deformities. Methods: This was a cross-sectional analytical study conducted with patients diagnosed with SMA who were treated at a Rare Diseases Reference Service in Recife, Pernambuco, Brazil. Serum vitamin D levels and their association with clinical characteristics of the disease, including SMA type, motor impairment, and the presence of musculoskeletal deformities were evaluated. Motor impairment was classified according to functional capacity, and an ordinal score was used for correlation analysis. Results: The sample consisted of 36 patients with SMA. The mean serum 25(OH)D concentration was 28.95 ± 10.28 ng/mL, with values ranging from 8.3 to 49.4 ng/mL. Based on the predefined cutoff of 30 ng/mL, 58.3% of participants had serum 25(OH)D concentrations below 30 ng/mL, whereas 41.7% had concentrations ≥30 ng/mL. Serum 25(OH)D concentrations differed significantly across motor function groups (p = 0.002). However, correlation analysis showed a weak and non-significant correlation between motor impairment and serum 25(OH)D concentrations (Spearman r = −0.136; p = 0.431; (n = 36). An association between hypovitaminosis D and the presence of musculoskeletal deformities was also observed. Conclusions: Hypovitaminosis D showed a high prevalence in patients with SMA. Although serum 25(OH)D concentrations differed significantly across motor function groups, the correlation between motor impairment and serum 25(OH)D concentrations was weak and non-significant. These findings reinforce the importance of monitoring serum vitamin D levels and adopting clinical and nutritional follow-up strategies in this population.