Spinal muscular atrophy (SMA) is a genetic disorder that causes a child to lose a specific type of cell in their spinal cord (motor neurons) and a part of their brain that is connected to the spinal cord (brain stem). Without these important parts of the brain and spinal cord, an affected child loses control of muscle movement, has muscle weakness, and loses muscle tissue (atrophy). The most commonly affected muscles are in the shoulders, hips, and thighs, but muscles involved in breathing and swallowing can also be affected in severe cases. There are many different types of SMA, each with its own set of features and symptoms. These include SMA types I through IV, X-linked, spinal muscular atrophy lower extremity dominant (SMA-LED), and adult-onset spinal muscular atrophy. More information about each type is available under a separate disease description.
While every type of SMA is caused by a change (mutation) in a gene, not every type has the same genetic cause. A mutation in the SMN1 gene is the genetic cause of SMA types I through IV. A mutation in the UBA1 gene is the genetic cause for X-linked SMA. A mutation in the DYNC1H1 gene is the cause for SMA-LED and a mutation in the VAPB gene is the cause of adult onset SMA. Each of these genes provide instructions for the body to make a protein that helps motor neurons work. Motor neurons are cells that send signals from the brain to the muscles. When one of these genes has a mutation, the motor neurons do not work, which causes the symptoms of SMA.
SMA is considered in a baby or child who has muscle weakness and atrophy. Genetic testing is used to confirm the diagnosis. There is no cure for SMA and treatments for more severe symptoms, such as breathing and swallowing problems, can include devices to help breathing and feeding. If your child has been diagnosed with SMA, talk with your doctor about current treatment options. Support groups can provide more information and support.