Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a group of genetic diseases that affects the part of the nervous system that controls voluntary muscle movements, such as crawling, walking, head and neck control and swallowing. The disease causes weakness and wasting of the voluntary muscles.

Most nerve cells that control muscles, called motor neurons, are located in the spinal cord. Motor neurons send electrical and chemical messages to the muscles. In SMA, the motor neurons don't send enough signals to the muscle cells, the muscles don't function properly and the muscles deteriorate.

SMA affects infants, children and adults. It's estimated that the condition occurs at a rate of 1 in every 6,000 births. Childhood SMA is an autosomal recessive disease, meaning it runs in families. Children inherit a gene from both their mother and father, although parents may not have symptoms. An estimated 1 in 40 "normal" people are carriers of the SMA gene. If both a man and woman carry the gene, their child has a 25 percent chance of developing the condition.

For more information or to make an appointment, please contact:
Pediatric Muscular Dystrophy Clinic

Reviewed by health care specialists at UCSF Children's Hospital.
Last updated May 8, 2007