FDA Approves Scholar Rock’s SMA Therapy to Improve Muscle Function

Rare Daily Staff

The U.S. Food and Drug Administration has approved Scholar Rock’s Isembyld for adults and children ages 2 and older with spinal muscular atrophy, a rare neuromuscular disease, who are already receiving an SMN2-targeted therapy.

The decision introduces the first approved spinal muscular atrophy (SMA) treatment designed to act directly on muscle, rather than solely preserving motor neurons. Current SMN-targeted medicines have transformed SMA care by helping preserve motor neurons, but they do not directly target muscle tissue, where weakness and atrophy can continue to affect independence over time.

SMA results from the loss of motor neurons, the nerve cells that send signals from the brain and spinal cord to muscles. As those cells are damaged or lost, voluntary muscles in the arms, legs and trunk become weaker and smaller. The effects can vary widely, from severe weakness beginning in infancy to forms diagnosed later in childhood or adulthood. The condition can limit a person’s ability to sit, stand, walk, eat, breathe and carry out everyday activities.

Isembyld is approved for adults and children ages 2 and older who are currently receiving an SMN2-targeted treatment, such as nusinersen or risdiplam. Those established therapies address the underlying shortage of survival motor neuron protein and are intended to protect the nerve cells that control muscles. Isembyld is designed to complement them by addressing declining muscle function.

The approval is significant for the SMA community because people with the disease can continue to lose strength and motor abilities even while receiving medicines that slow motor-neuron damage.

Isembyld is a monoclonal antibody that blocks the activation of myostatin, a protein involved in regulating muscle growth. By inhibiting myostatin signaling, the treatment is intended to make muscles more responsive and support improved motor function.

For families living with SMA, even modest changes in strength or function can have practical consequences. They may affect wheelchair transfers, self-care, reaching, eating, school participation, employment and the ability to sustain social activities.

“Motor function decline in SMA patients is affected by motor neuron health and muscle responsiveness,” Scholar Rock said in its announcement. “SMN-targeted treatments are designed to prevent motor neuron loss but do not directly address muscle.”

Isembyld will be administered by intravenous infusion, generally once every four weeks. Scholar Rock said eligible patients may receive infusions in a hospital, an infusion center or, in some cases, at home.

The FDA also awarded Scholar Rock a Rare Pediatric Disease Priority Review Voucher as part of the approval. The voucher may be used to obtain priority review for a future marketing application, subject to FDA program requirements.