Spinal Muscular Atrophy
What is spinal muscular atrophy?
Spinal muscular atrophy (SMA) is a condition caused by the body not being able to produce a specific protein that is required for nerve cells to control muscles. People with spinal muscular atrophy develop muscle weakness which usually gets worse over time, eventually affecting the muscles required for breathing. There are five types of spinal muscular atrophy, called types 0 through type 4. Type 0 is the most severe, with muscle weakness present at birth, while people with type 4 often do not show symptoms until adulthood.
How common is spinal muscular atrophy?
Spinal muscular atrophy affects about 1 in 10,000 babies each year in the United States.
What can be done for spinal muscular atrophy?
Identifying this condition early (soon after birth) can improve the ability to manage the symptoms of spinal muscular atrophy and improve the quality of life. Clinical trials for drugs that can be used to treat some symptoms of the condition are also underway.
How is spinal muscular atrophy inherited?
Spinal muscular atrophy is caused by changes in the SMN1 gene. It is a recessive inherited condition, which means that a person must have two altered copies of the SMN1 gene, usually one from each parent, in order to have the disease. People who have just one copy of the altered SMN1 gene are called carriers, and are not expected to have symptoms of the condition. If a baby is identified as a carrier for spinal muscular atrophy through Eli screening, genetic counseling and additional testing in the parents is recommended.
For babies who are found to have two SMN1 gene alterations, and therefore are diagnosed with spinal muscular atrophy, the severity of the condition is in part due to a second gene called SMN2. The number of copies of the SMN2 gene that a person has determines how severe the spinal muscular atrophy is expected to be, with fewer SMN2 genes meaning more severe symptoms.