Abstract
INTRODUCTION: Onasemnogene abeparvovec is one of the three disease-modifying therapies available that can significantly improve the outcome of patients with 5q-spinal muscular atrophy. Therapy-induced thrombotic microangiopathy is an ultra-rare, but potentially life-threatening condition of not yet clearly defined aetiology. CASE PRESENTATION: A case of a 2-year-old patient with 5q-spinal muscular atrophy, who developed thrombotic microangiopathy after gene replacement therapy with onasemnogene abeparvovec, is described. This severe adverse event was promptly recognized and successfully treated with the complement C5 inhibitor. CONCLUSION: Thrombotic microangiopathy is an ultra-rare, but potentially life-threatening condition that can occur after onasemnogene abeparvovec therapy. Anticipation of these serious adverse events, its prompt recognition and treatment is crucial for a better outcome.