SMA type III is the mildest form of the disease and symptoms may not appear until the second year of life. Often, weakness is first noted in the shoulder muscles and proximal leg muscles. Weakness is progressive and will eventually become profound, but children may survive into early adulthood. Genetic counseling is recommended for prospective parents with a family history of spinal muscular atrophy. There is no treatment for the progressive weakness caused by the disease.
Supportive care is important.
Attention must be paid to the respiratory system as affected people have difficulty clearing secretions and respiratory complications are common. Physiotherapy is important to prevent contractures and scoliosis . Bracing may be necessary. The less severe form is compatible with a longer lifespan. However, progressive weakness and debility are present in all forms.