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FDA Okays Expensive Gene Therapy for Infantile-Onset Spinal Muscular Atrophy
By Rajaneesh K. Gopinath, Ph.D.
Apart from becoming the first and only gene therapy to receive FDA approval for this indication, Zolgensma also turned out to be the world’s most expensive drug priced at $2.1 million.
Last week, the U.S. Food and Drug Administration announced the approval of AveXis’ Zolgensma (onasemnogene abeparvovec-xioi) making it the first and only gene therapy to be approved for the treatment of children less than two years suffering from infantile-onset Spinal muscular atrophy (SMA). Acting FDA Commissioner Ned Sharpless, M.D. shared his excitement. “Today’s approval marks another milestone in the transformational power of gene and cell therapies to treat a wide range of diseases. With each new approval, we see this exciting area of science continue to move beyond the concept phase into reality” he said.
SMA, a Leading Genetic Cause of Infant Mortality
Motor neurons are specialized nerve cells present in the anterior horn of the spinal cord. These cells receive impulses from the brain and in turn transmit them to the muscles to control their movement. SMA is a rare, inherited neuromuscular disorder that is characterized by the loss of motor neurons caused due to the insufficient production of functional survival motor neuron (SMN) protein. A majority of patients suffering from this genetic disease contain a mutation in the SMN1 or SMN2 gene and display muscle weakness, muscle wasting (atrophy) and severe outcomes such as inability to breathe or swallow. Depending upon the age of onset and severity, SMA is divided into four primary subtypes, among which infantile-onset SMA is the most common and serious. This makes the disease, the leading cause of genetic infant death with around 450 to 500 infants affected in the US annually.
Clinical Trial Data Leading to Zolgensma’s Approval
Zolgensma is an adeno-associated virus vector-based gene therapy in which a fully functional copy of human SMN gene is delivered into the target motor neurons. Children receiving a one-time intravenous injection showed improvement in their symptoms indicating sufficient expression of the SMN protein in the motor neurons. Zolgensma was submitted for FDA approval in October last year and as an acknowledgment of its efficacy, the drug received Priority Review. The initial clinical results were so promising that the drug received a Breakthrough Therapy designation back in 2016, long before Avexis was acquired by Novartis.
The evaluation of Zolgensma’s safety and effectiveness is based on an ongoing Phase 3 STR1VE trial and a completed Phase 1 START trial. The trials involved a total of 36 patients with infantile-onset SMA in the age bracket of 2 weeks to 8 months at the start of the study. The primary evidence of effectiveness is based on results from the 21 patients (10 male and 11 female) treated with Zolgensma in the Phase 3 STR1VE trial. Among the 19 remaining patients, who range from 9.4 to 18.5 months, 13 of them are at least 14 months of age. In comparison to the patients with infantile-onset SMA, the Zolgensma treated subset demonstrated significant improvement in their ability to reach developmental motor milestones such as better head control and the ability to sit without support. The most common side effects include elevated liver enzymes and vomiting. Therefore, the drug comes with a serious liver injury warning.
“The approval of Zolgensma is a testament to the transformational impact gene therapies can have in reimagining the treatment of life-threatening genetic diseases like spinal muscular atrophy,” said Vas Narasimhan, CEO of Novartis. “We believe Zolgensma could create a lifetime of possibilities for the children and families impacted by this devastating condition.”
Competition from other SMA Drugs
Before this, the only available disease-modifying therapy that was FDA approved to treat SMA, was Biogen’s Spinraza (nusinersen) which also costs a lot. Although, Zolgensma is much more expensive, its developers claim its worth its tall price because it is easier to administer. At the moment, the treatment will cost $2.1 million or $425,000 annually for five years. Besides, Roche is developing an oral drug called risdiplam to treat a broad range of patients with SMA from 1 month to 60 years of age. It remains to be seen whether the three-way competition could bring down the cost of these SMA drugs in the future.
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