Spinal muscular atrophy

What is spinal muscular atrophy (SMA)?

Spinal muscular atrophy (SMA) is a degenerative problem that affects the nerves that control voluntary muscle movement.

Childhood onset occurs in one in 10,000 live births. 

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 1 (or SMN1) is found to be abnormal in SMA. There is a nearby gene called SMN2 that will determine how severe the disease will be.  However, both copies need to be affected to cause disease. If only one is affected, you are called a “carrier”. A “carrier” has an abnormal gene but no symptoms.

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.  However, in Wisconsin, there is discussion of testing newborns for the disease before they have symptoms.

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) - This is the most severe type of SMA and may be present at birth or shortly after. 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 2 to 3 years from breathing problems.
• Type II (intermediate form) - This form of SMA is seen in children from 6 months to 2 years of age. They typically have generalized muscle weakness and may require braces, walkers, or a wheelchair for assistance. Life expectancy may extend to the 20s and 30s. 
• Type III (also called Wohlfart-Kugelberg-Welander) - This form of SMA affects children between 3 and 17 years of age. 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 physician 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 physician will obtain a complete medical history of your child, and he/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 physician 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 current cure for spinal muscular atrophy.  However, for eligible patients, Children’s also offers Spinraza (nusinersen), a drug that was recently approved by the Federal Drug Administration (FDA) for the treatment of spinal muscular atrophy.

In addition, across the country, there are ongoing clinical trials looking for a cure. Please discuss available treatment options and concerns with your doctor. Even with treatment, some children may have problems breathing or eating. The neuromuscular program team will assist with ways for your child to obtain nutrition and be safe.