Spinal Muscular Atrophy (SMA) | Diagnosis & Treatment

How is spinal muscular atrophy diagnosed?

Spinal muscular atrophy (SMA) is sometimes difficult to diagnose, as symptoms can resemble other conditions or medical problems. Doctors usually diagnose SMA after a child has muscle weakness and decreased muscle tone.

If your clinician suspects SMA, they may use the following tests to diagnose the condition:

  • genetic blood tests, which can confirm the diagnosis of SMA
  • an electromyography (EMG) test that measures the electrical activity of a muscle or a group of muscles (in some cases)
  • a creatine kinase (CPK) test (to distinguish from other types of neuromuscular diseases, if necessary)

What are the treatment options for spinal muscular atrophy?

The recent discovery of the genetic cause of SMA has led to the development of two new treatment options — a gene replacement therapy called Zolgensma (previously AVXS-101) and a drug called nusinersen (brand name Spinraza). Both have shown promising results.

Gene therapy for SMA

SMA gene therapy is a one-time infusion that replaces the defective or missing SMN1 gene with a working copy. This new gene increases survival motor neuron (SMN) protein levels, which improves motor neuron function and increases the likelihood of survival. Recently, the FDA approved this treatment for children less than 2 years of age with SMA. Learn more about gene therapy for SMA.

Nusinersen: Medication for SMA

Can my child use nusinersen?

To be treated with nusinersen, your child must have the SMN1 mutation that causes this disease. The FDA approved the use of this drug for all types of SMA with an SMN1 mutation, from infant-onset SMA type 1 to adult-onset SMA type 4.

How does nusinersen work?

SMA is caused by absence of both copies of the survival motor neuron gene 1, also known as SMN1. All people with SMA have a number of copies of the survival motor neuron gene 2, called SMN2. But the SMN2 gene produces only a small amount of functional SMN protein; the more copies of the SMN2 gene a child has, the milder the disease.

Nusinersen uses synthetic (man-made) genetic material called antisense oliigonucliotide to improve the splicing of the SMN2 gene. This helps children to make more SMN protein needed for healthy motor neurons.

Will my child benefit?

That may depend on the type of SMA your child has. The greatest effects of nusinersen have been seen in infants with SMA type 1, who participated in the ENDEAR trial. These children were enrolled before 7 months of age. In the trial, study investigators saw infants reaching developmental milestones like head control, rolling over, and sitting and standing. A small number of children were able to walk with support. Historically, 90 percent of children with SMA type 1 have passed away before their second birthday unless given aggressive respiratory support.

The CHERISH trial studied the effects of nusinersen in children ages 2 to 12 with SMA type 2. The changes were positive. However, children with severely limited mobility, chronic respiratory failure, swallowing problems, severe joint contractures or severe scoliosis were not included in the CHERISH trial. Therefore, the effects of nusinersen in children with more advanced SMA type 2 will likely vary from child to child. 

Nusinersen has been studied in SMA type 3, but not in a controlled way. Open-label studies show some signs of benefit — for example, some patients were able to walk longer on a six-minute walk test.

We don’t yet know whether nusinersen will help people with adult-onset SMA (type 4).

Overall, the results from clinical trials show that the earlier treatment starts and the longer a child is treated, the better the outcome will be. Nusinersen does not work in everyone. Also, we still don’t know how long the benefits will last, since we have only followed children for, at most, several years. The risk and benefits of this drug will be reviewed with the patient, family and medical team on a regular basis.

How is nusinersen given?

Nusinersen is injected directly into the spinal canal (intrathecally). This requires a lumbar puncture or spinal tap. Your child’s care team individualizes the injection process based on their health and needs.

It’s important to be still during the lumbar puncture. Some children may need anesthesia to sleep through the procedure. Children with spinal fusions may need an interventional radiology procedure to safely give the drug.

We start treatment by giving four 12 mg doses of nusinersen. After that, we give the same dose of this drug once every four months. We believe children will most likely need this treatment for life.

Is there a shortage of nusinersen?

No, there is enough supply of the drug.