SMA patients have a high risk of osteoporosis, but limited data are available, and management of bone fragility is not included in the standard of care.
This multicenter, retrospective, cross-sectional study aims to evaluate fragility fracture prevalence and bone mineral density (BMD Z-score) in untreated SMA patients, analyzing data collected from the ITASMAC registry.
Fracture history was available in 148 SMA patients (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 years for SMA3. Long bone fractures were the most prevalent (93%), and only 9% fractured patients were treated with bisphosphonates.
DXA scans before the first fracture were available in 82 patients, performed at a median age of 5 years for SMA1 (n= 3), 15 for SMA2 (n=37), and 27 for SMA3 (n=42). Pathologic BMD Z-scores (below -2) 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 summary, we found a fractures prevalence of 30%, in a large cohort of untreated SMA patients, with no significant differences between SMA types. BMD Z-scores were significantly lower in SMA1 and SMA2 compared to SMA3. This baseline analysis serves as a starting point for longitudinal studies to determine the effects of drug treatments on SMA bone health.