Spinal Muscular Atrophy
Spinal Muscular Atrophy refers to a group of hereditary diseases that damages and kills specialized nerve cells in the brain and spinal cord (called motor neurons). Motor neurons control movement in the arms, legs, face, chest, throat and tongue, as well as skeletal muscle activity including speaking, walking, swallowing and breathing.
The most common form of SMA is caused by an abnormal or missing gene known as the survival motor neuron gene 1 (SMN1), which is responsible for the production of a protein essential to motor neurons. This form of SMA has four types:
- Type l, also called Werdnig-Hoffman disease or infantile-onset SMA, is usually evident before 6 months of age. The most severely affected children will have reduced movement and chronic shortening of muscles or tendons (called contractures). Other children may have symptoms including reduced muscle tone, lack of tendon reflexes, twitching, skeletal abnormalities, and problems swallowing and feeding. Without treatment, many affected children die before age 2 years.
- SMA Type ll is usually first noticed between the 6 and 18 months of age. Children can sit without support but are unable to stand or walk unaided. Children also may have respiratory difficulties. Life expectancy is reduced but most individuals live into adolescence or young adulthood.
- SMA Type lll (Kugelberg-Welander disease) is seen after age 18 months. Children can walk independently but may have difficulty walking or running, rising from a chair, or climbing stairs. Other complications may include curvature of the spine, contractures, and respiratory infections. With treatment, most individuals can have a normal lifespan.
- Individuals with SMA Type IV develop symptoms after age 21 years, with mild to moderate leg muscle weakness and other symptoms.
There is no cure for SMA. Treatment consists of managing the symptoms and preventing complications. Some patients may benefit from nusinersen (Spinraza™) or other newly developed gene therapies. Physical therapy, occupational therapy, and rehabilitation may help to improve posture, prevent joint immobility, and slow muscle weakness and atrophy.
Stretching and strengthening exercises may help reduce spasticity, increase range of motion, and keeps circulation flowing. Some individuals require additional therapy for speech, chewing, and swallowing difficulties. Applying heat may relieve muscle pain.
Assistive devices such as supports or braces, orthotics, speech synthesizers, and wheelchairs may help some people retain independence. Proper nutrition and a balanced diet are essential to maintaining weight and strength Non-invasive ventilation at night can prevent apnea in sleep, and some individuals may also require assisted ventilation due to muscle weakness in the neck, throat, and chest during daytime.
Pediatric physiatrists can help prescribe programs, therapy services, medication, braces, and equipment to maximize function in children and young adults with SMA.
NIH: National Institute of Neurological Disorders and Stroke