Disease-Modifying Drugs for Spinal Muscular Atrophy

As of early 2021, the United States Food and Drug Administration (FDA) has approved 3 drugs to treat spinal muscular atrophy (SMA). They work in different ways to increase the amount of “survival of motor neuron” (SMN) protein produced by motor neurons. This helps rescue motor neurons and prevent muscle wasting.1

These treatments are changing expected outcomes for many children with SMA. Starting treatment before symptoms begin dramatically improves survival rate and chance of achieving motor milestones. This is the main reason why every newborn should be tested for SMA.1

Talk to your doctor to determine if these drugs are right for your child. The decision between them depends on many personal factors, including age and disease severity. These drugs are also very expensive, and most families must rely on insurance coverage to afford treatment. Despite their benefits, the high prices limit their cost-effectiveness.2,3

Spinraza® (nusinersen)

In 2016, the FDA approved Spinraza as the first drug to treat children and adults with SMA. It is given by injection into the fluid around the spinal cord. Treatment usually starts with 4 initial doses over the course of 2 months. After that, 1 dose is given every 4 months. The cost of each dose is around $125,000.4,5

Spinraza works by increasing the ability of the back-up SMN2 gene to produce functional SMN protein. Spinraza is a type of “antisense” therapy. This means it uses short pieces of DNA or RNA (called “antisense oligonucleotides" or ASOs) to alter how cells use genetic material to make proteins. ASOs cannot reach spinal motor neurons from the bloodstream, so they must be injected directly.5,6

Two phase 3 clinical trials studied the efficacy of Spinraza. In the first trial (called Endear), infants with type 1 SMA treated with Spinraza showed better motor function, increased life expectancy, and a higher chance of achieving independent sitting. The second trial (called Cherish) showed positive results for children with type 2 or 3 SMA.7,8

Another ongoing study (called Nurture) has shown the importance of starting Spinraza early. When started before symptom begin, Spinraza drastically improves survival rate and chances of reaching motor milestones.9

Zolgensma® (onasemnogene abeparvovec-xioi)

In 2019, the FDA approved Zolgensma for children under 2 years old with SMA. It is given as a single intravenous (into the vein) infusion. The estimated cost of 1 dose is more than $2 million.4,5

Zolgensma is a type of “gene therapy.” This means it delivers genetic material to fix a genetic problem. Zolgensma works by delivering a functional SMN1 gene to motor neurons.5,6

In clinical trials (called Str1ve and Start), infants treated with Zolgensma showed increased survival rate, motor functioning, and chance of achieving independent sitting. Ongoing clinical trials (including Spr1nt) are studying the use of Zolgensma in people before they show symptoms.5,10-12

Evrysdi™ (risdiplam)

In 2020, the FDA approved Evrysdi as the first and only drug taken by mouth for SMA. As of early 2021, it is approved to treat people older than 2 months old with SMA. Evrysdi is given by mouth once a day after a meal using an oral syringe.4,5

Evrysdi works by increasing the ability of the back-up SMN2 gene to produce functional SMN protein. Unlike Spinraza, Evrysdi can reach the spinal motor neurons from the bloodstream. This is why Evrysdi can be given by mouth.5,6

Four phase 2 clinical trials are studying the efficacy of Evrysdi. Early results from 2 of these trials (called Firefish and Sunfish) have shown that Evrysdi improves motor functioning and health outcomes in people with types 1, 2, and 3 SMA.13-17

The other 2 trials (called Jewelfish and Rainbowfish) are testing Evrysdi in people who have received other disease-modifying treatments or who do not yet show symptoms.5,18

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Written by: Matt Zajac | Last reviewed: August 2021