About Spinal Muscular Atrophy
The New York Center for Rare Diseases supports the mission and guidelines of the Genetic and Rare Diseases Information Center (GARD). The following information is provided by the NIH.
Summary
Spinal muscular atrophy (SMA) is a group of genetic neuromuscular disorders that affect the nerve cells that control voluntary muscles (motor neurons). The loss of motor neurons causes progressive muscle weakness and loss of movement due to muscle wasting (atrophy). Many types of SMA mainly affect the muscles involved in walking, sitting, arm movement, and head control. Breathing and swallowing may also become difficult as the disease progresses in many types of SMA. In some types of SMA, the loss of motor neurons makes it hard to control movement of the hands and feet. SMA type 1, 2, 3, and 4 are caused by changes (pathogenic variants, also known as genetic changes) in the SMN1 gene and are inherited in an autosomal recessive manner. Extra copies of the nearby related gene, SMN2, modify the severity of SMA. There are other rarer types of SMA caused by changes in different genes. Other autosomal recessive forms include SMA with progressive myoclonic epilepsy (SMA-PME) caused by changes in the ASAH1 gene and SMA with respiratory distress 1 (SMARD1) caused by changes in the IGHMBP2 gene. X-linked forms include X-linked infantile SMA caused by changes in UBA1. Diagnosis of SMA is suspected by symptoms and confirmed by genetic testing.