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

Causes

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

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.

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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, they 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:

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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, 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 muscle 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?

Treatment

The FDA has approved two medications to treat SMA: nusinersen (Spinraza) and onasemnogene abeparvovec-xioi (Zolgensma). 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. 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. 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 only need to be done one time.

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In studies, onasemnogene abeparvovec-xioi helped children with SMA reach certain developmental milestones faster, like controlling their heads or sitting without support.

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, 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 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 his care. Check for support groups that can let you share your experiences with others who are in similar situations.

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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 help 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 have a better quality of life. Researchers are also working to find new drugs that improve symptoms.

Getting Support

The following organizations can offer you support:

  • Cure SMA – 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 individuals and families through local chapters and their website, including offering information to those newly diagnosed.
  • Muscular Dystrophy Association - has information and links to services and support groups in your area.
  • SMA Foundation  – mission is to accelerate development of treatment for SMA, working with researchers, developing clinical trials and helping to educate others about this genetic condition.
 
WebMD Medical Reference Reviewed by Hansa D. Bhargava, MD on May 23, 2019

Sources

SOURCES:

Genetics Home Reference: "Spinal muscular atrophy."

KidsHealth: "Spinal Muscular Atrophy (SMA)."

Muscular Dystrophy Association: "Spinal Muscular Atrophy."

Medscape: "Spinal Muscular Atrophy."

National Institute of Neurological Disorders and Stroke: "NINDS Spinal Muscular Atrophy Information."

Boston Children's Hospital: "Spinal Muscular Atrophy (SMA)."

Jennifer Trust for Spinal Muscular Therapy: "Adult Onset SMA."

Cure SMA: "Therapeutic Approaches."

New England Journal of Medicine: "Single-Dose Gene-Replacement Therapy for Spinal Muscular Atrophy."

Muscular Dystrophy UK: "Developing a genetic therapy for spinal muscular atrophy."

Science Advances: "Gene therapy rescues disease phenotype in a spinal muscular atrophy with respiratory distress type 1 (SMARD1) mouse model."

Columbia University Department of Neurology: "Q&A on Spinraza Treatment for Spinal Muscular Atrophy (SMA) Patients."

FDA: "FDA approves innovative gene therapy to treat pediatric patients with spinal muscular atrophy, a rare disease and leading genetic cause of infant mortality," "FDA approves first drug for spinal muscular atrophy."

Genetics Home Reference: "SMN1 gene," "SMN2 gene."

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