source: Children's National Hospital
What is spinal muscular atrophy (SMA)?
Spinal muscular atrophy is a genetic disease that affects the motor nerve cells in the spinal cord, resulting in progressive muscle wasting and weakness. It typically begins in infancy or childhood years and affects about 1 in 11,000 babies.
What causes spinal muscular atrophy?
SMA is an autosomal recessive disease. This means that both males and females are equally affected, and that changes or mutations in two copies of the SMN1 gene (typically, one inherited from each parent), are necessary to have the condition. About 1 in every 50 Americans is a carrier for SMA.
Testing for SMA is done by looking for deletions (in nearly 95 percent of cases of SMA) or in a smaller number of cases looking for mutations in the SMN1 gene. Symptomatic individuals of all ages can be tested through DNA studies typically done from a blood sample. In addition, in some cases, prenatal testing can identify expecting parents who are at risk of having a child with SMA, and when desired, further fetal testing can be done. When both parents are carriers, there is a one in four, or 25 percent, chance, with each pregnancy, to have a child with SMA.