What exactly is spinal muscular atrophy (SMA)?
SMA is a rare genetic disorder that causes progressive muscle weakness and wasting. It happens because of a loss of motor neurons, which are nerve cells in the brain and spinal cord that control voluntary movement.
The condition affects about 1 out of every 11,000 births in Show Full Answer
What exactly is spinal muscular atrophy (SMA)?
SMA is a rare genetic disorder that causes progressive muscle weakness and wasting. It happens because of a loss of motor neurons, which are nerve cells in the brain and spinal cord that control voluntary movement.
The condition affects about 1 out of every 11,000 births in the United States. While it impacts a small number of people, it's the leading genetic cause of infant mortality.
There are five main types of SMA (types 0, 1, 2, 3, and 4) that account for 95 percent of cases. These types are categorized based on how severe the symptoms are and when they begin:
- Type 0 is the most severe and begins before birth
- Type 1 typically affects infants
- Types 2 and 3 can begin in childhood through early adulthood
- Type 4 is the mildest and begins in adulthood
Depending on the type, symptoms can include:
- Respiratory problems
- Difficulty swallowing and chewing
- Limited motor function
- Inability to walk or loss of walking ability
- Mild to moderate muscle weakness
It's important to note that SMA doesn't affect intelligence - people with the condition are typically bright and alert.
December 31, 2025
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