Spinal Muscular Atrophy
What Is Spinal Muscular Atrophy (SMA)?
Spinal muscular atrophy (SMA) is a condition affecting the motor nerves that control muscular function. SMA makes activities such as crawling, walking, breathing and eating difficult for children.
The nerves affected by SMA don’t have enough of an important protein, so they can’t carry signals from the brain to the muscles. Without those signals, muscles weaken and decrease in mass (also known as atrophy).
SMA is caused by a change (mutation) in the survival motor neuron 1 gene (SMN1 gene). The SMN1 gene makes a protein known as survival motor neuron protein, which helps motor neurons grow and function properly.
Motor neurons control muscle movement. When a gene mutation decreases the amount of protein, a child loses motor neurons over time. That means muscle control gets worse over time as well.
The most common SMN1 change is a deletion. That means a piece of the gene is missing. Most people who have SMA have two deletions—one in each copy of the SMN1 gene. Roughly 5 percent of people who have SMA have one deleted copy, as well as a different change in the second copy of the SMN1 gene.