What Is Spinal Muscular Atrophy?

What Is Spinal Muscular Atrophy?

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 he can have trouble controlling head movement, sitting without help, and even walking. In some cases, he can have trouble swallowing and breathing as the disease progresses.

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 his intelligence in any way. He will still be able to make friends and socialize.


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

When this happens, his 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, he won't get SMA but will be a carrier of the disease. When your child grows up, he could pass the broken gene to his child.


Symptoms vary greatly, depending on the type of SMA:

Type 1. This is the most severe type of SMA. He may not be able to support his head or sit without help. He 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, he 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.

Getting a Diagnosis

SMA can sometimes 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 his head up or rolling over?
  • Does your child have trouble sitting or standing on his 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, he may take a blood sample from your child to check for missing or broken genes that can cause SMA.

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 check if they are sending messages to the muscles.

CT, or computed tomography. This is a powerful X-ray that makes detailed pictures of the inside of your child's body.

MRI, or magnetic resonance imaging. 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 cells through a needle in the muscle or through a small cut in your child's skin.

Questions for Your Doctor


  • 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 one medication to treat SMA: nusinersen (Spinraza). Studies show it helps about 40% of people who use it by slowing down the advance of the disease and making people stronger.

Doctors inject nusinersen into the fluid around your child's spinal cord. The procedure for the shot -- including preparation and recovery time -- can take at least 2 hours. Your child will need multiple shots.

Nusinersen is a type of gene therapy. It belongs to a group of drugs called antisense oligonucleotides that have small bits of man-made genetic material. They work by "modulating," or adjusting, the SMN2 gene.

Everyone who has spinal muscular atrophy has at least one copy of the SMN2 gene, and some people have more. The SMN2 gene isn't doing a good job of making a key protein that allows the cells that control muscles to work. Adjusting this gene can let it make more protein or a better-quality protein.

Besides adjusting the SMN2 gene, researchers are studying another type of gene therapy that involves replacing or correcting the SMN1 gene. Since spinal muscular atrophy is caused by a mutation -- or change -- in the SMN1 gene, doctors are checking to see if replacing or fixing it will treat the disease.


This method is also called "gene transfer." Scientists are looking for ways to put a copy of the faulty gene into cells in the area of the spinal cord.

Besides gene therapy, your doctor may suggest ways for your child to manage symptoms. Some methods that may be helpful are:

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, he may need a special mask or mouthpiece. For severe problems, your child may use a machine that helps him 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 his spine is still growing. When he's stopped growing, he may have surgery to fix the problem.

Taking Care of Your Child

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 him keep up with friendships and activities with your family.

Your child will likely need care throughout life from different types of doctors. He 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 getting the food your child needs to stay healthy
  • 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 his care. Check for support groups that can let you share your experiences with others who are in similar situations.


What to Expect

The outlook depends on when symptoms started and how severe they are. If your child has type 1, the most severe form of SMA, he 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 his development is delayed, and he 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 his life comfortable.

In other types of SMA, doctors can work to ease a child’s symptoms for many years, and in many cases throughout his 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 him keep up a better quality of life. Researchers are also working to find new drugs that improve symptoms.

Getting Support

You can get insights from parents who have kids with SMA on the website of Fight SMA. You can also find out about clinical trials.

The Muscular Dystrophy Association website has information and links to services and support groups in your area that can help if you are facing SMA.

WebMD Medical Reference Reviewed by Dan Brennan, MD on November 08, 2018



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