Low bone mineral density and reduced bone‐specific alkaline phosphatase in 5q spinal muscular atrophy type 2 and type 3: A 2‐year prospective study of bone health

Individuals with spinal muscular atrophy (SMA) are at risk of developing skeletal problems. This study investigated bone mineral density (BMD), bone turnover markers and motor function in children and adolescents with SMA type 2 and type 3 over a two-year period. The effect of nusinersen was studied in a subgroup.Single-centre study, including 20 patients, 2-18 years, of whom ten patients received nusinersen treatment. BMD was measured by dual-energy X-ray absorptiometry.All patients had low BMD levels at baseline; mean Z-score -2.3 for total body less head (TBLH) and -2.9 for total hip left (THL). Significant correlations were found both at baseline and for the follow-up change for motor function and Z-scores (TBLH and THL). For the whole study group, reduced bone formation and unchanged bone resorption, assessed by bone-specific alkaline phosphatase (BALP) (p = 0.0006, ES = -0.83) and C-terminal cross-linking telopeptide of type I collagen (CTX), respectively, were found over the study period. However, BALP decreased less in the nusinersen treatment group, which suggests a positive development on bone mass in these patients.Bone health evaluation is important in follow-up programmes for SMA patients. Further investigations are warranted for individuals on survival motor neuron-targeted treatments.