Adult spinal muscular atrophy (SMA) is one type of a group of genetic conditions, called spinal muscular atrophies, that affect specific cells in the spinal cord (motor neurons) and cause muscle weakness and loss of muscle tissue (atrophy). Symptoms of the adult form of SMA include weakness in the muscles that are closest to the chest (proximal), muscle cramping in the arms, legs and abdomen, and uncontrollable muscle movements. The disease can also affect swallowing, bowel movements or bladder function. Adult SMA begins in early to mid-adulthood. The symptoms of this form of SMA typically are not as severe, and become worse (progress) more slowly, than the other forms of SMA.
Adult SMA is caused by a change (mutation) in the VAPB gene. This gene provides instructions for the body to make a protein that helps keep abnormally folded proteins out of motor neurons, which are cells that send signals from the brain to the muscles. If the VAPB gene has a mutation, abnormally folded proteins build up and create clumps in the motor neurons, stopping them from sending signals and causing the symptoms of adult SMA. This condition is inherited in an autosomal dominant manner, which means a mutation in only one of the two gene copies a person has is enough to cause the condition.
A diagnosis of adult SMA is considered in an adult who starts to have muscle weakness and atrophy. The diagnosis is confirmed with genetic testing. Current treatment options depend on the symptoms and can include breathing and feeding support, therapies, and devices to help with movement (such as braces or a wheelchair). If you have been diagnosed with adult SMA, talk with your doctor about current treatment options. Meeting with a genetic counselor may be helpful to determine who else in the family is at risk for adult SMA. Support groups can provide additional information and connect you with others affected by this condition.