Spinal muscular atrophy (SMA) is a disease of the nerves and muscles caused by certain genes. It affects the motor neurons in the spinal cord. It causes muscle wasting and weakness.
SMA is caused by a faulty or missing gene called SMN1. SMA is an autosomal recessive disease. This means that both boys and girls are equally affected. And it means that one copy or missing copy of the faulty gene from each parent (2 total) are needed to cause the condition.
If both parents are carriers, they have a 1 in 4 chance for a child with SMA with each pregnancy. Carrier testing is usually done only if a child in the family is known to have SMA. In the U.S., newborns are now screened for the disease.
A child is more at risk for SMA if he or she has a parent or sibling with the disease.
There are several types of SMA that affect children. They vary in the age when symptoms first appear, the seriousness of symptoms, and how symptoms get worse. Symptoms can also occur a bit differently in each child. The different types of SMA include:
Type 0. This is the rarest and most severe type. It is found before a child is born. Newborns with this type may have joint or heart defects. They also have problems breathing. Many die within 6 months after birth.
Type 1. This is also called Werdnig-Hoffman or infantile-onset SMA. This is a very severe type of SMA and may be present at birth. Infants have problems holding up their head, sucking, feeding, and swallowing. They tend to move very little. The muscles of the chest are also affected. The child moves his or her tongue in wormlike movements. Children with type 1 often die by age 2 because of breathing problems.
Type 2. This is also called intermediate SMA. This form of SMA is seen in children from age 6 months to 18 months. Children with type 2 have overall muscle weakness. They may need braces, a walker, or a wheelchair. They can often live into adulthood.
Type 3. This is also called Kugelberg-Welander or mild SMA. Symptoms may appear in children between ages 2 and 17 years. These children show signs of clumsiness, trouble walking, and mild muscle weakness. They may have delayed motor development. Children with type 3 live long into their adult years.
A fourth type of SMA affects adults, typically in their 30s and 40s. It causes a walking disability.
The symptoms of SMA can be like other health conditions. Make sure your child sees a healthcare provider for a diagnosis.
SMA is sometimes hard to diagnose. The healthcare provider will ask about your child’s symptoms, past health, and your family’s health history. Your child will have a physical exam. Your child may also have tests, such as:
Blood and saliva tests. Babies may be screened for the condition shortly after birth. Older children may have tests that measure levels of a muscle enzyme (CK). Or they may have genetic tests to check for conditions that tend to run in families.
Muscle biopsy. For this test, a healthcare provider removes a small sample of the muscle and checks it under a microscope.
Electromyogram (EMG). This test measures the electrical activity of a muscle or a group of muscles. An EMG can show abnormal electrical muscle activity caused by conditions that affect the nerves and muscles.
Treatment will depend on your child’s symptoms, age, and general health. It will also depend on how severe the condition is.
There is no cure for SMA. The goals of treatment are to:
Prevent breathing problems in children who have affected breathing muscles
Give breathing support with a machine (ventilator) if needed
Give nutritional support to children whose swallowing muscles are affected
A new therapy called nusinersen is now available. It may help children with SMA achieve motor milestones that would not normally happen without treatment. This medicine is injected into the cerebrospinal fluid.
Your child may be able to try other SMA treatments that are still being tested in clinical trials. Talk with your child’s healthcare provider to find out if there are any clinical trials you should consider.
Talk with your child’s healthcare providers about the risks, benefits, and possible side effects of all treatments.
Depending on the type of SMA, possible complications may include:
Aspiration (when fluids or small bits of food get into the airways)
Contractions of muscles and tendons
Scoliosis, or curvature of the spine
Trouble breathing due to muscle weakness and scoliosis
SMA has no cure. Treatment is supportive. It focuses on preventing complications of weakness. The severity of muscle weakness determines likelihood of survival.
Your healthcare provider may advise genetic counseling. You can discuss with a counselor the risk for SMA in a future pregnancy.
The healthcare team will talk with you about how to best care for your child at home. Children with SMA need regular visits with their healthcare providers.
Call the healthcare provider if your child has:
Symptoms that don’t get better, or get worse
SMA is a disease of the nerves and muscles caused by certain genes. It affects the motor neurons in the spinal cord. It causes muscle wasting and weakness.
SMA is caused by a faulty or missing gene. Boys and girls are equally affected. One copy or missing copy of the faulty gene from each parent (2 total) is needed to cause the condition.
There are several types of SMA that affect children. They vary in the age when symptoms first appear, the seriousness of symptoms, and how symptoms get worse.
SMA has no cure. One new treatment can result in improved motor function. The other goals of treatment are to treat breathing and nutrition problems.
Your child may be able to try new SMA treatments that are still being tested in clinical trials. Talk with your child’s healthcare provider to find out if there are any clinical trials you should consider.
Tips to help you get the most from a visit to your child’s healthcare provider:
Know the reason for the visit and what you want to happen.
Before your visit, write down questions you want answered.
At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you for your child.
Know why a new medicine or treatment is prescribed and how it will help your child. Also know what the side effects are.
Ask if your child’s condition can be treated in other ways.
Know why a test or procedure is recommended and what the results could mean.
Know what to expect if your child does not take the medicine or have the test or procedure.
If your child has a follow-up appointment, write down the date, time, and purpose for that visit.
Know how you can contact your child’s provider after office hours. This is important if your child becomes ill and you have questions or need advice.