Beyond managing spinal muscular atrophy symptoms, are there any treatments for the condition itself?

Yes. There are a few treatments for spinal muscular atrophy that treat the disease by increasing the amount of survival motor neuron (SMN) protein in the body. These are known as disease-modifying, SMN-based or SMN-enhancing treatments.

In the majority of people with spinal muscular atrophy, the cause is an abnormal or missing (mutated) survival motor neuron 1 (SMN1) gene. The SMN1 gene is responsible for making the SMN protein, which motor neurons need to work.

Because of the SMN1 gene mutation, the motor neurons in a person with spinal muscular atrophy don't get enough SMN protein. This causes the motor neurons to shrink and eventually die, leading to progressively worsening muscle weakness and, for some, death.

The SMN protein is also made by another gene, the SMN2 gene, but it's a less stable form. Also, the number of SMN2 genes people have varies. People who have a less severe form of spinal muscular atrophy usually have more SMN2 genes.

FDA-approved disease-modifying treatments include:

  • Nusinersen (Spinraza). This drug is injected into the fluid surrounding the spinal cord. It increases the ability of SMN2 genes to make more SMN protein. The drug is approved for people of any age and with any type of spinal muscular atrophy. After several initial doses, it's given every several months. Possible side effects include respiratory infections and constipation, and the drug may affect the kidneys.
  • Onasemnogene abeparvovec-xioi (Zolgensma). This drug is given as an injection in a vein. It uses a virus to deliver a copy of the SMN1 gene to the body, to increase levels of SMN production. The drug is approved for children up to 2 years old. Steroids must also be taken with this drug, for a month, possibly more. Possible side effects include vomiting and an increase in certain other proteins in the body. The drug may also affect the liver.
  • Risdiplam (Evrysdi). This drug is taken by mouth. It boosts the ability of SMN2 genes to make a more stable SMN protein. The drug is approved for people 2 months of age and up. Possible side effects include fever, diarrhea, constipation, vomiting, rash and respiratory infections.

If you're considering SMN-enhancing treatments, it's important to start them early. This can help prevent the loss of motor neurons, which can't be replaced.

With

Duygu Selcen, M.D.

Sept. 23, 2020 See more Expert Answers