Spinal Muscular Atrophy

Medically Reviewed by Christopher Melinosky, MD on April 08, 2023
8 min read

Spinal muscular atrophy (SMA) most often affects babies and children and makes it hard for them to use their muscles. When your child has SMA, there's a breakdown of the nerve cells in the brain and spinal cord. The brain stops sending messages that control muscle movement.

When that happens, your child's muscles get weak and shrink, and children can have trouble controlling head movement, sitting without help, and even walking. In some cases, they can have trouble swallowing and breathing as the disease gets worse.

There are different types of SMA, and how serious it is depends on which type your child has. There's no cure, but treatments can improve some symptoms and, in some cases, help your child live longer. Researchers are working to find new ways to fight the disease.

Keep in mind that every child or adult who has SMA will have a different experience. No matter how much your child's movement is limited, the disease doesn't affect their intelligence in any way. They will still be able to make friends and socialize.

Symptoms vary a lot, depending on the type of SMA:

Type 0. This is the rarest and most severe form of SMA and develops while you’re still pregnant. Babies with this type of SMA move less in the womb and are born with joint problems, weak muscle tone, and weak muscles for breathing. They often do not survive due to breathing problems.

Type 1. This is also a severe type of SMA. A child may not be able to support their head or sit without help. They may have floppy arms and legs and problems swallowing.

The biggest concern is weakness in the muscles that control breathing. Most children with type 1 SMA don't live past age 2 because of breathing problems.

Keep in touch with your medical team, family members, clergy, and others who can help give you the emotional support you need while your child fights this disease.

Type 2. This affects children 6-18 months old. The symptoms range from moderate to severe and usually involve the legs more than the arms. Your child may be able to sit and walk or stand with help.

Type 2 is also called chronic infantile SMA.

Type 3. Symptoms for this type start when children are 2-17 years old. It's the mildest form of the disease. Your child will most likely be able to stand or walk without help but may have problems running, climbing stairs, or getting up from a chair. Later in life, they may need a wheelchair to get around.

Type 3 is also called Kugelberg-Welander disease or juvenile SMA.

Type 4. This form of SMA starts when you're an adult. You may have symptoms such as muscle weakness, twitching, or breathing problems. Usually, only your upper arms and legs are affected.

You'll have the symptoms throughout your life, but you can keep moving and even get better with exercises that you'll practice with the help of a physical therapist.

It's important to remember that there's a lot of variation in the way this type of SMA affects people. Many people, for instance, are able to keep working for many years. Ask your doctor about ways to meet with others who have the same condition and know what you're going through.

SMA is a disease that's passed down through families. If your child has SMA, it's because they have two copies of a broken gene, one from each parent.

When this happens, their body won't be able to make a specific kind of protein. Without it, the cells that control muscles die.

If your child gets a faulty gene from just one of you, they won't get SMA but will be a carrier of the disease. When your child grows up, they could pass the broken gene to their own child.

SMA can be hard to diagnose because the symptoms may be similar to other conditions. To help figure out what's going on, your doctor may ask you:

  • Has your baby missed any developmental milestones, such as holding their head up or rolling over?
  • Does your child have trouble sitting or standing on their own?
  • Have you seen your child have trouble breathing?
  • When did you first notice the symptoms?
  • Has anyone in your family had similar symptoms?

Your doctor may also order some tests that can help make a diagnosis. For example, they may take a blood sample from your child to check for missing or broken genes that can cause SMA. Your doctor could also order a blood test that checks for creatine kinase (CK). It’s an enzyme that leaks out of weakening muscles. High blood CK levels aren’t always harmful but do show possible muscle damage.

Other tests rule out conditions that have similar symptoms:

  • Nerve tests, such as an electromyogram (EMG). Your doctor puts small patches on your child's skin and sends electrical impulses through the nerves to see if they are sending messages to the muscles.
  • CT. This is a powerful X-ray that makes detailed pictures of the inside of your child's body.
  • MRI. This uses powerful magnets and radio waves to make pictures of organs and structures inside your child.
  • Muscle tissue biopsy. In this test, the doctor removes muscle cells through a needle in the muscle or through a small cut in your child's skin.
  • Have you treated others with this condition?
  • What treatments do you recommend?
  • Is there therapy that can help keep my child's muscles strong?
  • What can I do to help my child become more independent?
  • How can I get in touch with others who have family members with SMA?

The FDA has approved three medications to treat SMA: nusinersen (Spinraza), onasemnogene abeparvovec-xioi (Zolgensma) and risdiplam (Evrysdi). Both are forms of gene therapy that affect the genes involved in SMA. The SMN1 and SMN2 genes give your body instructions for making a protein that helps with controlling muscle movement.

  • Nusinersen (Spinraza). This treatment adjusts the SMN2 gene and lets it make more protein. It's used for both children and adults with SMA. Your child's medical team will inject the drug into the fluid around their spinal cord. Including preparation and recovery time, this can take at least 2 hours and will need to be done several times, followed by another dose every 4 months. Studies show it helps about 40% of people who use it by making them stronger and slowing the disease.
  • Onasemnogene abeparvovec-xioi (Zolgensma). This involves replacing the problem SMN1 gene. It's used for children under 2 years old. Your child's medical team will put a tiny tube called a catheter directly into a vein in their arm or hand (an IV). Then, they'll send a copy of the SMN gene through the tube into a specific group of motor neuron cells. This will need to be done only one time. In studies, onasemnogene abeparvovec-xioi helped children with SMA reach certain developmental milestones faster, like controlling their heads or sitting without support.
  • Risdiplam (Evrysdi). This treatment works to stop the SMN2 genes from disrupting the protein production,  allowing the protein to reach the nerve cells as needed. Your child takes it orally once a day after a meal. The dosage is determined by their weight.Clinical trials showed improved muscle function after 12 months in 41% of those taking it.

Besides gene therapy, your doctor may suggest a few other ways to help manage symptoms:

  • Breathing. With SMA, especially types 1 and 2, weak muscles keep air from moving easily in and out of the lungs. If this happens to your child, they may need a special mask or mouthpiece. For severe problems, your child may use a machine that helps them breathe.
  • Swallowing and nutrition. When muscles in the mouth and throat are weak, babies and children with SMA can have a hard time sucking and swallowing. In that situation, your child may not get good nutrition and may have trouble growing. Your doctor may suggest working with a nutritionist. Some babies may need a feeding tube.
  • Movement. Physical and occupational therapy, which use exercises and regular daily activities, can help protect your child's joints and keep muscles strong. A therapist may suggest leg braces, a walker, or an electric wheelchair. Special tools can control computers and phones and help with writing and drawing.
  • Back issues. When SMA starts in childhood, children can get a curve in their spine. A doctor may suggest that your child wear a back brace while their spine is still growing. When they’ve stopped growing, they may have surgery to fix the problem.

There's a lot you can do as a family to help your child with some of the basic tasks of daily life. A team of doctors, therapists, and support groups can help you with your child's care and let them keep up with friendships and activities with your family.

Your child will probably need lifelong care from different types of doctors. They may need to see:

  • Pulmonologists, doctors who treat lungs
  • Neurologists, specialists in nerve problems
  • Orthopedists, doctors who treat bone problems
  • Gastroenterologists, specialists in stomach disorders
  • Nutritionists, experts in the way food affects your child's health
  • Physical therapists, people trained in using exercise to improve your child's motion

This team can help you make decisions about your child's health. It's important not to let yourself get overwhelmed by the task of managing care. Check for support groups that can let you share your experiences with others who are in similar situations.

The outlook depends on when symptoms started and how severe they are. If your child has type 1, a severe form of SMA, they may start having symptoms anywhere from birth to age 6 months. In general, most babies with this type start showing signs of the disease by age 3 months. You'll start to notice that their development is delayed, and they may not be able to sit up or crawl.

Even though children with this type usually don't live beyond age 2, with help from your doctors and support team, you can make their life comfortable.

In other types of SMA, doctors can help ease a child’s symptoms for many years and, in many cases, throughout their life.

Keep in mind that every child or adult who has SMA will have a different experience. A treatment plan that's made just for your child can help them have a better quality of life.

Organizations like these can offer you support:

  • Cure SMA. It funds research aimed at treating and curing SMA. Its SMArt Moves initiative focuses on the importance of early diagnosis and treatment. Cure SMA also offers support for people and families through local chapters and its website, including offering information to those newly diagnosed.
  • Muscular Dystrophy Association. This group has information and links to services and support groups in your area.
  • SMA Foundation. Its mission is to boost the search for SMA treatment, working with researchers, developing clinical trials, and helping to educate others about this genetic condition.