146P Investigation of bone health in a large cohort of naïve SMA patients

SMA patients have a high risk of osteoporosis although limited data are available, and bone fragility management is not fully integrated in the standard of care. This multicenter, retrospective, cross-sectional study aims to evaluate fracture prevalence and bone mineral density (BMD Z-score) in naïve SMA patients included in the ITASMAC registry data, by using hospital charts and dual-energy X-ray absorptiometry (DXA) measurements. Data were available in 148 SMA patients from 11 National referral center for SMA (6.1% SMA1, 42.6% SMA2, and 51.3% SMA3). Overall, 46/148 (31.1%) patients presented at least 1 fragility fracture, 2/9 SMA1 (22.2%), 20/63 SMA2 (32.3%), and 24/76 SMA3 (31.6%), at a mean age of 12 years for SMA1 and SMA2, and 31 for SMA3. Long bone fractures were the most prevalent (93%), and only 4/46 (9%) of fractured patients were treated with bisphosphonates. DXA scans before the first fracture were available in 82 patients, performed at median age of 5 years for SMA1 (n= 3), 15 for SMA2 (n=37), and 27 for SMA3 (n=42). Pathologic BMD Z-scores were observed in 3/3 (100%) SMA1, 35/37 (95%) SMA2, and 21/42 (50%) SMA3. The lowest median BMD Z-scores were registered at femur (-2.9), followed by total body (-2.5) and lumbar spine (-2.2). In conclusion, we detected an overall fractures prevalence of 30%, without significant differences between SMA types. BMD Z-scores were significantly lower in SMA1 and SMA2 compared to SMA3. This baseline analysis of bone health in naïve SMA patients, provides a starting point for longitudinal studies to determine SMA treatment effects on bone in this condition.