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Novel Gene Therapy for Pediatric Spinal Muscular Atrophy

Rare SMA is Leading Genetic Cause of Infant Mortality

AveXis Inc. has received FDA approval for Zolgensma (onasemnogene abeparvovec-xioi), the first gene therapy approved for children aged below 2 years with spinal muscular atrophy (SMA), the most severe form of the disease.

The rare SMA is caused by a mutation in the survival motor neuron 1 (SMN1) gene, and is typically classified into several subtypes based on age of onset and severity. Infantile-onset SMA is the most severe and most common form, and children with SMA have difficulty holding their head up, swallowing, and breathing. Most do not survive past early childhood.

Onasemnogene abeparvovec-xioi is an adeno-associated virus vector-based gene therapy that targets the cause of SMA. A single intravenous administration causes the expression of the SMN protein in the motor neurons, improving muscle movement and function, and survival.

The safety and effectiveness of onasemnogene abeparvovec-xioi are based on trials involving 36 children with infantile-onset SMA aged between approximately 2 weeks and 8 months at study entry. Patients treated with the drug also showed significant improvement in their ability to reach developmental motor milestones, such as head control and sitting without support, compared to the natural history of patients with the disease.

The most common side effects of onasemnogene abeparvovec-xioi are elevated liver enzymes and vomiting.

The FDA granted this application fast track, breakthrough therapy, priority review, and orphan drug designations. The agency also awarded AveXis a rare pediatric disease priority review voucher for onasemnogene abeparvovec-xioi.

Source: FDA, May 24, 2019

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