US FDA Grants Expanded Approval of ELEVIDYS Gene Therapy for DMD Patients Ages 4 and Above

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Muscular Dystrophy Association Celebrates FDA Approval of Viltolarsen for Treatment of Duchenne Muscular Dystrophy Amenable to Exon 53 Skipping

This is the third approved exon-skipping therapy for Duchenne muscular dystrophy.

New York, NY – August 12, 2020 — The Muscular Dystrophy Association (MDA) today celebrated the decision by the US Food and Drug Administration (FDA) to grant accelerated marketing approval to viltolarsen (Viltepso) for the treatment of Duchenne muscular dystrophy (DMD) in patients amenable to skipping exon 53. It is the third exon-skipping, disease-modifying drug to treat DMD, the most common childhood form of muscular dystrophy. Viltepso will be made available in the United States and marketed by NS Pharma, a wholly owned subsidiary of the Japanese company Nippon Shinyaku Co. Ltd.

In September 2016, the approval of eteplirsen (marketed by Sarepta as Exondys 51) marked a watershed moment for treating neuromuscular diseases with gene-targeting therapies such as exon skipping. Approval in December 2019 off Vyondys 53, another exon-skipping drug designed to treat a different subset of DMD individuals than those who qualify for Exondys 51, was another significant step forward in the development of therapies for DMD — and all neuromuscular diseases — that target the root cause of the disease. With the current approval, Viltepso joins Vyondys 53 as a targeted treatment available to patients with DMD amenable to exon 53 skipping.


"The approval of Viltepso provides another option for patients with Duchenne, a disease that, up until a few years ago, had no approved therapies," says MDA’s Executive Vice President, Chief Research Officer Sharon Hesterlee, PhD. "It adds to the arsenal of gene-targeting therapies, and it may spur the development of more disease-modifying therapies to treat other neuromuscular diseases as the promise of effective genetic medicines comes to reality through the commitment of researchers and families."

DMD is caused by mutations in the dystrophin gene (DMD) on the X chromosome that result in little or no production of dystrophin, a protein essential to keeping muscle cells intact. Viltepso is called an “exon-skipping” drug in that it is designed to target and promote skipping over a section of genetic code in order to avoid the gene mutation and produce more of the dystrophin protein. It is estimated that up to 8% of patients with DMD have mutations amenable to treatment with Viltepso. Although treatment with the drug will not cure DMD, it could slow progression of the disease, which, in turn, could extend the length of time individuals with DMD could walk, eat independently, and breathe without assistance.

The FDA’s decision to approve Viltepso highlights the importance of years of commitment to supporting and funding breakthrough research by MDA and others into gene identification and unlocking the cause of DMD. MDA-supported research has been central to the development of the exon-skipping approach behind both Exondys 51, Vyondys 53, and Viltepso from the beginning, having funded foundational work upon which the strategy was built as well as extensive research into the strategy since that time. Laboratory development of exon-skipping therapies began in the 1990s, including notably with MDA-funded work by Steve Wilton, PhD, and colleagues. Their work led to the invention of what would later become Exondys 51, Vyondys 53, and Viltepso.

Since its inception, MDA has committed more than $218 million to DMD and Becker muscular dystrophy research and more than $1 billion across the spectrum of neuromuscular diseases. While this may be the second exon-skipping therapy for treating DMD, the increasing pace of drug development holds immense promise for the future of all neuromuscular diseases. Of the now 12 approved therapies for treating neuromuscular diseases, ten have been approved by the FDA in the past decade alone.

Clinical trials support approval of Viltepso

Viltepso was evaluated in two clinical studies with a total of 32 male patients with genetically confirmed DMD. The most common side effects observed during the two clinical studies were: upper respiratory tract infection, injection site reaction, cough and fever.

The FDA based its decision to grant accelerated approval to Viltepso on the positive results of the phase 2 study to assess safety, tolerability, and dose, followed by a 20-week open-label treatment period, in sixteen ambulant boys (ages 4-9) with DMD amenable to skipping exon 53.

At the end of the phase 2 study, treatment with Viltepso was associated with significant increases in dystrophin levels, seen in patients as young as 4 year old and after six months or fewer of treatment. Additional secondary outcomes included gross motor skill assessment using timed function tests and quantitative muscle testing. All patients receiving Viltepso showed significant improvements in timed function tests at the 25-week visit. Consistent with the FDA’s accelerated approval pathway, the continued approval of Viltepso may be contingent on confirmation of a clinical benefit in a post-marketing confirmatory trial (RACER53), which is currently enrolling and expected to conclude by 2024.

In March 2020, viltolarsen was approved in Japan for the treatment of patients with DMD amenable to skipping exon 53.

About NS Support

NS Support is a patient support program designed to provide patients with information to help navigate the process of starting and staying on therapy. NS Support can be reached by telephone at 833-677-8778, Monday through Friday from 8 am to 8 pm ET. Caregivers and healthcare providers can call to learn more information about NS Support and request notifications about product availability and program enrollment.

MDA’s Resource Center provides support, guidance, and resources for patients and families, including information about the approval of Viltepso, open clinical trials, and other services. Contact the MDA Resource Center at 1-833-ASK-MDA1 or

About DMD

DMD occurs in 1 in every 3,500 to 5,000 males born worldwide. The disease primarily affects boys, but in rare cases it can affect girls. Onset of symptoms occurs in early childhood, usually between ages 3 and 5. Muscle weakness can begin as early as age 3, first affecting the muscles of the hips, pelvic area, thighs, and shoulders, and later the skeletal (voluntary) muscles in the arms, legs, and trunk. The calves often are enlarged. By the early teens, the heart and respiratory muscles also are affected.

About Viltepso

Viltepso uses NS Pharma’s exon-skipping technology to target exon 53 of the DMD gene. Exon skipping is a treatment strategy in which sections of genetic code are “skipped” (spliced out, or left out) during the protein manufacturing process, allowing cells to create shortened but partially functional dystrophin protein, the muscle protein missing in DMD. Exon skipping is not a cure for DMD but potentially could lessen the severe muscle weakness and atrophy that is the hallmark of the disease.

Just as individuals with DMD caused by a mutation that would be amenable to skipping exon 51 could benefit from treatment with Exondys 51, those with DMD caused by a mutation that would be impacted by skipping exon 53 could benefit from treatment with Vyondys 53, and now the newly approved Viltepso.

About the Muscular Dystrophy Association

For 70 years, the Muscular Dystrophy Association (MDA) has been committed to transforming the lives of people living with muscular dystrophy, ALS, and related neuromuscular diseases. We do this through innovations in science and innovations in care. As the largest source of funding for neuromuscular disease research outside of the federal government, MDA has committed more than $1 billion since our inception to accelerate the discovery of therapies and cures. Research we have supported is directly linked to life-changing therapies across multiple neuromuscular diseases. MDA's MOVR is the first and only data hub that aggregates clinical, genetic, and patient-reported data for multiple neuromuscular diseases to improve health outcomes and accelerate drug development. MDA supports the largest network of multidisciplinary clinics providing best in class care at more than 150 of the nation's top medical institutions. Our Resource Center serves the community with one-on-one specialized support, and we offer educational conferences, events, and materials for families and healthcare providers. Each year thousands of children and young adults learn vital life skills and gain independence at summer camp and through recreational programs, at no cost to families. During the COVID-19 pandemic, MDA continues to produce virtual events and programming to support our community when in-person events and activities are not possible. MDA's COVID-19 guidelines and virtual events are posted at For more information, visit