Spinal muscular atrophy (SMA): Types and treatment

Spinal muscular atrophy is a genetic disorder in which a person cannot control the movement of their muscles, due to a loss of nerve cells in the spinal cord and the brainstem.

Muscle wasting and weakness results, making it difficult to stand, walk, control head movements, and even, in some cases, to breathe and to swallow.

Spinal muscular atrophy (SMA) is not just one condition but a range of diseases. Grouped together, the different types of SMA form the second leading cause of neuromuscular disease.

SMA is present in 1 in every 6,000 to 10,000 live births. It is the second most common fatal autosomal recessive disorder after cystic fibrosis.

If SMA affects an infant under the age of 2 years, it is usually fatal. If the patient is older when the disease appears, they will have a different type of SMA, and life expectancy may be normal.

There is no cure for SMA, but in December 2016, the first drug to treat it was approved: Spinraza.

Fast facts on spinal muscular atrophy:

Here are some key points about spinal muscular atrophy (SMA). More detail is in the main article.

There are different types of SMA. They vary in severity.

It is a genetic condition.

The main symptom is muscle weakness and muscle loss. In severe cases, respiratory problems may occur.

Treatments include supportive devices to help the patient breathe, and a new drug, Spinraza.

SMA cannot be prevented, but prospective parents can request genetic testing if they may be carriers.


There are different types of SMA. They vary in terms of when they start to appear in an individual, and in the life expectancy that a person with the disorder will have.

SMA type I

Spinal muscular atrophy
Spinal muscular atrophy affects physical function but not necessarily intellectual ability.

SMA type I is a serious condition. Children with this disorder never manage to sit or stand. It is usually fatal before the age of 2 years.

It can be detected before birth, as there may be a reduction in fetal movement during the final months of pregnancy. If not, it will become evident within the first few months of life.

Infants with SMA type I never sit or stand, and they do not usually survive to the age of two years. SMA type I is also known as Werdnig-Hoffmann disease.

SMA type II

SMA type II usually appears between the ages of 3 and 15 months. The infant may learn to sit, but will never be able to stand or walk.

Life expectancy depends on whether or not the patient develops breathing problems. Most people with SMA type II survive into adulthood.

SMA type III

SMA type III, or Kugelberg-Welander disease, appears between 2 and 17 years of age.

Symptoms include an unusual gait and difficulty running, climbing steps, or rising from a chair. There may be a slight tremor of the fingers. Some people may lose the ability to walk, and they may also develop scoliosis. Complications include obesity and osteoporosis.

Kennedy syndrome

Kennedy syndrome is also known as progressive spinobulbar muscular atrophy. Kennedy syndrome is a slowly progressive, inherited condition that usually appears between 20 and 40 years of age, but it can appear later.

Women carry the gene, but only a son will inherit the disorder.

Congenital SMA with arthrogryposis

Congenital SMA with arthrogryposis is a rare disorder. People with this condition will have a persistent contracture of joints, known as arthrogryposis.

The condition is evident at birth. Features include severe contractures, curvature of the spine, chest deformity, respiratory problems, an unusually small jaw, and drooping upper eyelids.

Adult SMA

Adult SMA, or SMA IV, begins after the age of 18 years. People with this condition can walk, and they do not have problems with breathing or eating.

Researchers have also found links between SMA and amyotrophic lateral sclerosis (ALS), commonly called Lou Gehrig’s disease.

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