Scapuloperoneal spinal muscular atrophy (SPSMA) is a very rare genetic disorder that causes muscle weakness and a decrease of muscle tissue (atrophy) that gets worse with time (progressive). In SPSMA, the weakness and atrophy tend to occur in the muscles of the shoulders (scapula) and lower legs (peroneal), but muscles of the face and voice box (larynx) may also be affected. The symptoms of SPSMA generally begin early in life, either in infancy or early childhood.
SPSMA is caused by a mutation in the TRPV4 gene. This gene provides instructions for the body to make a protein that allows calcium into or out of cells in the body and is important in motor neurons (cells that carry signals from the brain to the muscles of the body). When the TRPV4 gene has a change (mutation), it affects how the brain communicates with the muscles through the motor neurons, leading to weakness and atrophy in the muscles.
SPSMA seems to be inherited in an autosomal dominant manner, meaning that a mutation in one of the two copies a person has is enough to cause the disorder. However, not everyone who has a mutation in the TRPV4 gene will have symptoms (incomplete penetrance). A diagnosis of SPSMA is considered in children with muscle weakness in the shoulders and lower legs. Genetic testing is used to confirm the diagnosis. If your child has been diagnosed with this disease, talk with your doctor about the current treatment options. Support groups are a good resource for additional information and to connect with other families affected by this condition.