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FDA approves first gene therapy for spinal muscular atrophy in children

The FDA on Friday approved the first gene therapy for children aged 2 years or younger with spinal muscular atrophy, a leading genetic cause of infant mortality, according to an agency press release.

Zolgensma (onasemnogene abeparvovec-xioi, AveXis Inc.) is an adeno-associated virus vector-based gene therapy that targets the cause of spinal muscular atrophy (SMA). The vector delivers a fully functional copy of human SMN gene into the target motor neuron cells, according to the FDA. A one-time IV administration of the gene therapy results in expression of the SMN protein in a child’s motor neurons, which improves muscle movement and function, and survival of a child with SMA. Dosing is determined based on the weight of the patient.

“Today’s approval marks another milestone in the transformational power of gene and cell therapies to treat a wide range of diseases,” Ned Sharpless, MD, acting FDA commissioner, said in the release. “With each new approval, we see this exciting area of science continue to move beyond the concept phase into reality. The potential for gene therapy products to change the lives of those patients who may have faced a terminal condition, or worse, death, provides hope for the future.”

SMA is a rare genetic disease caused by a mutation in the SMN1 gene. SMA caused by mutations in the SMN1 gene is generally classified into several subtypes, based on the age of onset and severity; infantile-onset SMA is the most severe and most common subtype. Children with this condition have problems holding their head up, swallowing and breathing, according to the FDA. These symptoms may be present at birth or may present by age 6 months.

The safety and effectiveness of the gene therapy is based on an ongoing clinical trial and a completed clinical trial involving 36 pediatric patients with infantile-onset SMA aged approximately 2 weeks to 8 months at study entry, according to the release. The primary evidence of effectiveness is based on results from the 21 patients treated with onasemnogene abeparvovec-xioi in the ongoing clinical trial. In this trial, there are 19 remaining patients aged 9 to 19 months. Compared with the natural history of patients with infantile-onset SMA, patients treated with the gene therapy also demonstrated significant improvement in their ability to reach developmental motor milestones, including head control and the ability to sit without support, according to the release.

The most common adverse effects of onasemnogene abeparvovec-xioi are elevated liver enzymes and vomiting. The gene therapy has a boxed warning that acute serious liver injury can occur. Patients with pre-existing liver impairment may be at higher risk for experiencing serious liver injury. Clinical examination and laboratory tests to assess liver function should be completed before treatment with onasemnogene abeparvovec-xioi, and patients’ liver function should be monitored for at least 3 months after administration of therapy.

Certain vaccines are contraindicated for patients on a substantially immunosuppressive steroid dose. Caregivers should consult with their health care professional to determine whether adjustments to the patient’s vaccination schedule are necessary to accommodate concomitant corticosteroid administration.

The FDA granted this application fast track, breakthrough therapy and priority review designations. The gene therapy also received orphan drug designation. The FDA also awarded the manufacturer a rare pediatric disease priority review voucher, under a program intended to encourage the development of new drugs and biological products for the prevention and treatment of certain rare pediatric diseases. – by Regina Schaffer

Disclosure s : Sharpless is acting commissioner of the FDA. AveXis Inc. is a Novartis company.