The US FDA has approved apitegromab-mstn (Isembyld) for the treatment of spinal muscular atrophy (SMA) in adults and pediatric patients aged 2 years and older who are currently receiving an SMN2-targeted treatment. Apitegromab is the first approved SMA therapy that directly targets muscle loss and works alongside existing treatments. Mechanism of Action Apitegromab is a fully human IgG4 monoclonal antibody that binds to promyostatin and latent myostatin and inhibits myostatin activation and blocks myostatin signaling.

Clinical Evidence The efficacy of apitegromab was evaluated in a clinical trial involving 188 patients aged 2 to 21 years with 5q SMA. All patients were receiving an approved SMN2-targeted treatment, either nusinersen or risdiplam, and were nonambulatory at baseline. Key findings at 1 year in patients aged 2 to 12 years: Significant improvement in the Hammersmith…