Bone Health in Children with Spinal Muscular Atrophy

Objectives: The bone health status in children with spinal muscular atrophy (SMA) on disease-modifying drugs is not known. This study evaluates the bone health status in children with SMA.

Methods: This is a prospective study of children with molecular confirmed SMA. Information on the SMA type, disease-modifying drug used, Dual X-ray absorptiometry (DXA) findings, and vitamin D levels, are collected.

Results: Thirty-two paediatric patients including 8 with SMA type 1, 14 with type 2, and 10 with type 3, were recruited. The male to female ratio was 3:5. The mean age was 11.3 ± 5.5 years. Twenty-six patients had been on nusinersen for a mean duration of 2.7 ± 1.3 years, while 7 had been on Risdiplam for 0.3 ± 0.2 years. Their mean 25OH-vitamin D level was 84 ± 44 nmol/L. Only three had vitamin D insufficiency. DXA performed in 15 patients (14 on either nusinersen or risdiplam) confirmed low bone mineral density (BMD) with a Z-score < 2 in 14 out of the 15 patients. Four had a history of long bone fractures and three were put on intravenous bisphosphonates.

DXA sites BMD Z-scores Total-body-less-head -4.7 ± 1.5 Lumber spine -1.8 ± 1.7 Lateral distal femur (region 1) -3.1 ± 1.9 Lateral distal femur (region 2) -3.5 ± 1.5 Lateral distal femur (region 3) -3.0 ± 1.4

Conclusion: Low BMD was common in children with SMA even on disease-modifying treatments. To maximize the effectiveness of these drugs, an effective treatment to improve bone health is needed.
Keywords: spinal muscular atrophy: bone health; disease-modifying treatment