Spinal muscular atrophy type 2 (SMA2) is one type of a group of conditions known as spinal muscular atrophies (SMAs). SMAs are inherited disorders that cause a child to lose a specific type of cell in their spinal cord (motor neurons) and a part of their brain that is connected to the spinal cord (brain stem). Without these important parts of the brain and spinal cord, an affected child loses control of muscle movement, has muscle weakness, and loses muscle tissue (atrophy). Muscle weakness in SMA2 is first noticed between the ages of 6 and 12 months. Children with SMA2 can usually sit without support, but need help getting to a seated position. Development is delayed and affected children usually cannot stand or walk. Many children with SMA2 lose the ability to sit on their own by their mid-teens. Other symptoms of this disease can include curvature of the spine (scoliosis) and uncontrollable movement in the fingers (tremors). Most affected individuals live past the age of 25 years.
SMA2 is caused by changes (mutations) in the SMN1 gene. This gene provides instructions to make a protein that helps motor neurons work. Motor neurons are cells that send signals from the brain to the muscles. When there are mutations in the SMN1 gene, the motor neurons die off, leading to the symptoms of this condition. SMA2 is inherited in an autosomal recessive way, which means a child must have a mutation in both copies of their SMN1 gene to have the condition.
SMA2 is usually considered in a child who has significant muscle weakness that is noticed between 6 and 12 months of age. Genetic testing of the SMN1 gene is used to confirm the diagnosis. There is no cure for SMA2. Treatment options, such as braces to help support the back or legs, are available to help manage the symptoms of SMA2. Talk to a doctor about all treatment options. Support groups are available for additional information and to connect with other families affected by SMA2.