Spinal Muscular Atrophy (SMA)

Fact: Spinal muscular atrophy (SMA) most often affects babies and children

What is spinal muscular atrophy?
Spinal muscular atrophy (SMA) is a genetic disease affecting the part of the nervous system that controls voluntary muscle movement.

Most of the nerve cells that control muscles are located in the spinal cord, which accounts for the word spinal in the name of the disease. SMA is muscular because its primary effect is on muscles, which don’t receive signals from these nerve cells. Atrophy is the medical term for getting smaller, which is what generally happens to muscles when they’re not active.

SMA involves the loss of nerve cells called motor neurons in the spinal cord and is classified as a motor neuron disease.

In the most common form of SMA (chromosome 5 SMA, or SMN-related SMA), there is wide variability in age of onset, symptoms and rate of progression. In order to account for these differences, the chromosome 5 SMA often is classified into types 1 through 4.

The age at which SMA symptoms begin roughly correlates with the degree to which motor function is affected: The earlier the age of onset, the greater the impact on motor function. Children who display symptoms at birth or in infancy typically have the lowest level of functioning (type 1). SMA onset in children (types 2 and 3), teens or adults (type 4) generally correlates with increasingly higher levels of motor function.

Spinal muscular atrophy (SMA) most often affects babies and children and makes it hard for them to use their muscles.

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 or she 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.

Your child's treatment depends on his symptoms and the type of SMA he has. The goal is to help your child move better and be as independent as possible.While your child is getting treatment, you can let him take part in as many activities for his age group as possible.

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 develop curves in their spines. 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.

Want to learn more?

The following are organizations and/or websites dedicated to providing information and education surrounding Spinal Muscular Atrophy. These organizations are dedicated to research, education, awareness, and/or support. They are listed in Alphabetical order without any preference or prejudice. Listing these organizations is not a recommendation or referral in any regard for seeking treatment or consultation or support for treatment.

U.S. National Library of Medicine

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