Endocrine Abstracts

Background: Recently introduced disease modifying treatments have dramatically changed the clinical course of spinal muscular atrophy (SMA) and improved survival. Children are now encountering more long-term complications. Bone fragility is a poorly understood complication and whether disease modifying drugs affect bone health (and fragility) is yet to be determined. Our aim was to describe bone health in children with SMA under the care of a tertiary UK children’s hospital.

Method: A retrospective case notes review was conducted of all paediatric patients with SMA at our tertiary centre in 2025. Clinical data on fracture frequency, bone mineral density (BMD), bone biochemistry and vitamin D supplementation were collected.

Results: Twenty-nine children with SMA (Type 1 = 16, Type 2 = 8, Type 3 = 4 and pre-symptomatic =1) were included. Median age was 7 years (range 2-15). All children were receiving disease modifying drugs (11 onasemnogene abeparvovec (OA), 3 nusinersen and 16 risdiplam). Fifteen children had switched from one drug to another (7 nusinersen to OA and 9 nusinersen to risdiplam). Of children aged 5-15 years, 12/24 underwent DXA scans. All had low BMD on at least one scan. Mean total body less head (TBLH) Z-score was -3.09 (SD +/- 0.49) and lumbar spine Z-score was -2.42 (SD +/- 1.14). Mean BMD Z-scores were lower in children with Type 1 than those with Type 2 and Type 3. Four children (Type 1=3 and Type 2 = 1) had a combined total of five fractures, four femoral and one vertebral, all caused by low trauma mechanisms. 97% of children received vitamin D supplementation and mean vitamin D levels was 64nmol/l (SD +/- 20). Two children who sustained fractures received bisphosphonate treatment for bone fragility.

Conclusion: Our pilot data showed a high prevalence of low BMD in children with SMA who underwent DXA scans. Moreover, although uncommon, fractures sustained were caused by minimal trauma. Vertebral fractures were however rare. A multi-centre retrospective study (SMA-ABC) is now underway to further contribute to the understanding of bone health in this population and inform future management plans.