An autosomal recessive disorder of muscle weakness and wasting caused when the motor nerves that stimulate and control muscles fail to function. As a result, the muscles atrophy. There are a variety of presentations of the disorder. Severity of symptoms can range from life threatening in Type I SMA, to mild weakness in the adult form. At present, there is no treatment or cure. The gene for SMA is on chromosome 5, and is due to a mutation in the survival motor neuron gene. All of the autosomal recessive forms of SMA are due to mutations in the survival motor neuron gene, but the severity of the disease is influenced by the function of a related gene (survival motor neuron gene 2). The better the function of the survival motor neuron 2 gene, the milder the clinical features.
an inherited neuromuscular disorder that affects motor neurons, which control movement of voluntary muscles; three groups, based on age of clinical onset, are recognized