Spinal muscular atrophy (SMA) is a genetic condition that affects a child’s range of movement due to the ongoing degeneration of muscle tone.
This is usually noticed in infancy when the child fails to make the usual developmental milestones, such as rolling over, sitting up, crawling and walking. The muscle tone will continue to waste away over time, with the muscles closest to the center of the body, such as the shoulders, chest and back, being affected more than those in the extremities.
In severe cases, as the muscle deteriorates the child will begin to lose the ability to walk, sit unaided, and eventually move. In types 3 and 4, problems may appear with running and walking, balance, tremors, and twitching in adulthood.