Evolution of bone mineral density, bone metabolism and fragility fractures in Spinal Muscular Atrophy (SMA) types 2 and 3

•Natural history data of bone involvement and metabolism in SMA are still limited.•Young children with SMA can present low 25-OH D levels and vertebral fractures.•BMD decreases and bone resorption markers increase over time.•Higher spine BMD values at follow up were associated with HFMSE score >12 at baseline. With recent advances in the treatment of Spinal Muscular Atrophy (SMA), there is a strong need to increase knowledge on the involvement of organs and systems outside the central nervous system. We investigated bone metabolism, bone mineral density (BMD) and fractures, and their possible correlation with age and motor capacities. Thirty-two children with SMA (27 type 2, 5 type 3), mean age 40 ± 32.3 months, underwent two evaluations at an 18-month interval (V1 and V2). Twelve of these children also underwent a third evaluation at month 36 (V3). Diet, bone metabolism, BMD, X-rays, and motor function (by the Hammersmith Functional Motor Scale Expanded – HFMSE – and the Upper Limb Module – ULM) were assessed. At V1, 25-OH vitamin D3 (25OH D) therapy was started, and dietary calcium intake adjusted according to the recommended dietary allowance. Low 25OH D levels and asymptomatic vertebral fractures were mainly observed at V1. At all visits, bone resorption markers were higher than normal. At V2 and V3, decreased BMD was observed. Higher spine BMD values at follow-up were associated with HFMSE score >12 at baseline (p