Spinal muscle atrophy (SMA) is a serious heritable disease characterized by the loss of motor neurons. Motor neurons are nerve cells that control the movement of voluntary muscles. As the disease progresses, patients lose the ability to move, swallow, talk, and even breathe.
The disease is caused by a mutation in the SMN1 gene, which contains the information necessary to make the SMN protein that is essential for the survival of motor neurons. A second gene called SMN2 can also produce the SMN protein, but not in amounts necessary for motor neuron health.
SMA is divided into types based on the age of disease onset and the severity of its symptoms. Severity is thought to depend on the SMN2 gene copy number that a patient has, although this is not the only determinant. There are also some rare cases of SMA that are caused by mutations in genes other than SMN1.
What is SMA Type 2?
SMA type 2, also called intermediate SMA or chronic infantile SMA, is marked by symptoms that usually appear between 7 and 18 months of age.
The earliest symptoms of SMA type 2 are often a delay of developmental ability, such as difficulty in sitting independently or sitting without support.
Muscle weakness is usually more apparent in the legs than the arms.
Some children may have difficulty swallowing and may have an increased susceptibility to respiratory infections.
Approximately 70 percent of the children with SMA type 2 do not have deep tendon reflexes, affecting joints and reducing limb movement. Many patients also have tremors affecting the fingers.
Some children are able to crawl or stand with assistance or bracing, but most likely will never be able to walk unaided.
Cognition and mental ability are not affected by the disease — children with SMA type 2 are generally alert, bright, and responsive. Special educational programs are not necessary, though assistance with the physical demands of schooling may be.
Following a preliminary diagnosis based on symptoms and family history, a physician will take a small blood sample from the child and send it for genetic testing. It generally takes between two and four weeks to receive test results.
There is currently no cure for SMA. However, treatments can help to manage symptoms of the disease.
Parents of a child with SMA type 2 will need to meet with a multidisciplinary health care team to ensure that their child is receiving needed care. This will include a physiotherapist or an occupational therapist who can help parents support their child in learning to move and speak. The physiotherapist can design an individualized exercise program, while the occupational therapists can prescribe aids and adaptations such as braces or a wheelchair to maximize mobility.
The outlook for patients with SMA type 2 depends on the age of diagnosis, and the early care and support they receive, especially with respiration. While some people with SMA type 2 succumb to the disease at an early age, many survive into adulthood.
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