What is spinal muscular atrophy (SMA)?

Spinal muscular atrophy is a genetic disease that affects the spinal cord and nerves, resulting in muscle wasting and weakness.

What causes spinal muscular atrophy?

SMA is an autosomal recessive disease. This means that both males and females are equally affected, and that two copies of the gene, one inherited from each parent, are necessary to have the condition.

A gene called survival motor neuron (or SMN) is found to have an abnormal area (either a deletion or extra copy of the gene) in over 95 percent of cases of SMA. Symptomatic individuals of all ages can be tested through DNA studies typically done from a blood sample.

When both parents are carriers, there is a one in four, or 25 percent, chance, with each pregnancy, to have a child with SMA. Carrier testing for the general population is technically difficult and usually available only if a previously affected child in the family has been studied.

What are the symptoms of spinal muscular atrophy?

Spinal muscular atrophy is sometimes difficult to diagnose, as symptoms can resemble other conditions or medical problems. Each child may experience symptoms differently. There are four types of spinal muscular atrophy based on symptoms and age of onset. The child may have the following symptoms:

  • Type I (also called Werdnig-Hoffman or infantile-onset SMA). This is the most severe type of SMA and may be present at birth. Infants have problems holding their head, sucking, feeding, swallowing, and typically move very little. The muscles of the chest are also affected. The motion of the tongue is described as having "worm-like" movements. Death results usually by the age of two to six years from breathing problems.

  • Type II (juvenile SMA, intermediate SMA, or chronic SMA). This form of SMA is seen in children from six months to 18 months of age. They typically have generalized muscle weakness and may require braces, walkers, or a wheelchair for assistance. Life-expectancy often extends into adulthood.

  • Type III [also called (Wohlfart-)Kugelberg-Welander or mild SMA]. This form of SMA affects children older than 18 months of age or as late as adolescence. These children show signs of clumsiness, difficulty walking, mild muscle weakness, and may be developmentally delayed. These children live long into their adult years.

  • Type IV. This form of SMA affects adults in their 30s and 40s, resulting in a walking disability.

The symptoms of spinal muscular atrophy may resemble other problems or medical conditions. Always consult your child's doctor for a diagnosis.

How is spinal muscular atrophy diagnosed?

The diagnosis of spinal muscular atrophy is made after the sudden or gradual onset of specific symptoms and after diagnostic testing. During the physical examination, your child's doctor will obtain a complete medical history of your child, and he or she may also ask if there is a family history of any medical problems.

Diagnostic tests that may be performed to confirm the diagnosis of spinal muscular atrophy include the following:

  • Blood tests

  • Muscle biopsy. A small sample of the muscle is removed and examined to determine and confirm a diagnosis or condition.

  • Genetic tests. Diagnostic tests that evaluate for conditions that have a tendency to run in families.

  • Electromyogram (EMG). A test that measures the electrical activity of a muscle or a group of muscles. An EMG can detect abnormal electrical muscle activity due to diseases and neuromuscular conditions.

Treatment of spinal muscular atrophy

Specific treatment for spinal muscular atrophy will be determined by your child's doctor based on:

  • Your child's age, overall health, and medical history

  • The extent of the condition

  • The type of spinal muscular atrophy

  • Your child's tolerance for specific medications, procedures, or therapies

  • Expectations for the course of the condition

  • Your opinion or preference

There is no cure for spinal muscular atrophy. The key to medically managing spinal muscular atrophy is through early detection.

The goal of treatment is to prevent respiratory problems and provide adequate nutritional care to the child since the swallowing and breathing muscles can be affected by this condition.

The extent of the problem is dependent on the severity of the condition and the presence of other problems that could affect the child. In severe cases, a breathing machine may be required to help the child breathe easier.

The health care team educates the family after hospitalization on how to best care for their child at home and outlines specific clinical problems that require immediate medical attention by his or her doctor. A child with spinal muscular atrophy requires frequent medical evaluations throughout his or her lifespan.