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SMA and 3 Other Neuromuscular Disorders That Affect Breathing

Medically reviewed by Dennrik Abrahan, M.D. — Written by Emily Wagner, M.S.
Posted on May 16, 2023

Breathing is an automatic body function that we often take for granted. For individuals living with neuromuscular disorders (NMDs) such as spinal muscular atrophy (SMA), even the simplest act of breathing can become a challenge. Among these NMDs, SMA is one of the most well known, but others can also affect a person’s ability to breathe properly.

SMA is an NMD that affects the motor neurons, which are responsible for muscle function and movement. SMA and other NMDs also affect the muscles supporting the lungs, which can make breathing difficult. Some children and adults with these disorders need breathing support or medications to improve their condition.

In this article, we’ll discuss how SMA and other NMDs are associated with breathing problems. Because each disease affects muscles differently, we’ll explain how they affect pulmonary function (lung function) and what treatments are available to help.

1. Spinal Muscular Atrophy

SMA is an NMD caused by mutations (changes in a DNA sequence of a gene, which can affect the way the gene works) in the survival motor neuron 1 (SMN1) gene. This gene provides instructions for making the SMN1 protein, a protein required for nerve cells to send signals from the brain to muscles. Without these signals, the muscles can’t move and they begin to atrophy (waste away).

There are five types of SMA — from 0 to 4 — that vary in severity. Type 0 begins before birth and is the most severe form. Type 4 begins in adulthood and is the mildest form. Many children and adults with SMA type 0, 1, 2, or 3 have breathing difficulties. Eventually, respiratory insufficiency can limit the life span of many people living with SMA type 1 or type 2. Respiratory insufficiency happens when the respiratory system can’t take in enough oxygen or get rid of enough carbon dioxide from the body, causing breathing problems that can be serious or even life-threatening. Children with SMA type 3 can also experience breathing difficulties, especially after they are no longer able to walk.

The muscles in the chest wall between the ribs — known as the intercostal muscles — are weak in people with SMA. Normally, these muscles help the chest expand and fill with air. In SMA, these muscles can’t expand as well, causing hypoventilation (difficulty breathing deeply in a normal rhythm). Infants with SMA also have a hard time sucking and swallowing, which can cause them to inhale liquids or food. This is known as aspiration, and it increases the risk of pneumonia and other lung problems.

Spinal Muscular Atrophy With Respiratory Distress Type 1

An extremely rare type of SMA that affects breathing is SMA with respiratory distress type 1 (SMARD1). This disease affects specific nerve cells known as alpha motor neurons, which are found in the spinal cord. They’re responsible for triggering muscles to squeeze or contract.

SMARD1 is diagnosed in infants between the ages of 6 weeks and 6 months who are experiencing respiratory failure (trouble breathing). The motor neurons that control the diaphragm — the flat muscle along the bottom of the rib cage that pushes air out of the lungs — and abdomen don’t work properly, making it hard to breathe. Unless infants with SMARD1 receive ventilation treatment, many die from respiratory failure at around 1 year old.

SMA type 1 and SMARD1 have similar characteristics. The first sign of SMA type 1 in infants is having weak or “floppy” muscles, and they develop breathing problems later on. The first signs of SMARD1 are early breathing problems and some muscle weakness.

Ventilation and SMA Treatments Improve Breathing

Children and adults with SMA and breathing difficulties should see a pulmonologist (lung specialist) a few times a year to check on their health. Since they can’t breathe as well, many people with SMA are at an increased risk of respiratory tract infections like pneumonia. It’s essential to work with a pulmonologist to find ways for you or your child to clear the lungs, remove mucus, and support breathing, especially while sleeping.

Depending on how severe SMA is, mechanical ventilation may be needed to help you or your child breathe properly. Your pulmonologist will discuss the different options and which is best for you (or your child’s case). Most children with SMA type 1 usually need extra assistance with breathing, which often involves invasive methods such as using an endotracheal tube for ventilation. This tube is placed in the mouth during a medical emergency if the child has a sudden decline in breathing. If the pulmonologist believes that the breathing is getting worse to the point where it could endanger the child’s life, they may suggest a tracheostomy tube. This tube is inserted through a small hole in the neck into the windpipe and is attached to a ventilator, which can help with breathing problems in the long term.

Those with SMA type 2 or 3 can often use noninvasive ventilation, such as a bilevel positive airway pressure (BiPAP) machine. This machine uses a mask placed over the nose and mouth that helps move air in and out of the lungs. It’s also used to help treat nocturnal hypoventilation (shallow breathing when sleeping) and sleep apnea (when you stop breathing while sleeping).

In addition to a pulmonologist, children with SMA need a care team of specialists. These people typically include a gastroenterologist and a team to help manage nutrition, dental hygiene, psychiatry, social work, case management, and in some cases, palliative care (improve quality of life rather than focus on a cure, for those with serious illnesses). Doctors and researchers also continue to develop new treatments for SMA that improve quality of life and respiratory care. These new therapies still need long-term studies to better understand their effects and overall impact.

2. Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an NMD caused by mutations in the gene for making the protein dystrophin. This protein is important for making muscle fibers — without it, muscle cells begin to die off and can’t be replaced. DMD typically begins in early childhood, affecting children under the age of 6. Becker muscular dystrophy is a milder form of DMD.

Children with DMD have a progressive loss of muscle function, starting with the muscles in their legs. They may have trouble walking, running, or climbing stairs. Scoliosis, bending of the spine, is also common in DMD. As the disease progresses, breathing difficulties and heart problems happen more often. Scoliosis can change the shape of the chest, making it harder for the lungs and diaphragm to work. Children with DMD eventually develop breathing difficulties and respiratory failure.

Many children with DMD also develop dilated cardiomyopathy (heart disease). The heart’s walls become thin over time, making it harder for it to pump blood to the rest of the body. Symptoms of dilated cardiomyopathy include shortness of breath, chest pain, and fatigue. Many children with DMD begin taking blood pressure medications at an early age to help slow down heart disease and prevent heart failure.

3. Myasthenia Gravis

Myasthenia gravis is an autoimmune disorder caused by the body’s immune system attacking the muscles. Specifically, those with the condition have antibodies that target the neuromuscular junctions where the nerve endings and muscles communicate with one another. When these junctions are destroyed, nerve cells can’t send signals to the muscles anymore, causing muscle weakness.

The muscles most often affected by myasthenia gravis control voluntary movement in the mouth, eyes, arms, legs, and throat. Breathing problems can occur during a myasthenia crisis, one of the most serious complications of myasthenia gravis. The chest muscles and diaphragm become weak, making it difficult to breathe without assistance. If the throat muscles are weak, mucus and other secretions can build up, blocking the throat and airway.

A myasthenia crisis can be brought on by a respiratory infection or stress. Up to 20 percent of people with myasthenia gravis will have at least one myasthenia crisis in their lifetime. A person with a myasthenia crisis will need ventilation until they can breathe on their own again.

4. Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis, also called ALS or Lou Gehrig’s disease, is a rare NMD that progressively affects motor neurons, causing muscle twitching and wasting. Symptoms of early ALS include stiff, spastic, or weak muscles and trouble talking, chewing, and swallowing.

As ALS progresses, many people have trouble with voluntary movements using their arms and legs. The inspiratory and expiratory muscles, which help move air in and out while breathing, eventually become paralyzed. Most people with ALS need a BiPAP machine to help them breathe at night.

In the later stages of ALS, a tracheostomy is usually needed for breathing. Respiratory failure is the most common cause of death in ALS, typically within five years of the first symptoms. However, as respiratory therapy and ventilation methods improve, some people with ALS live a decade or longer.

Talk With Others Who Understand

On mySMAteam, the social network for people with SMA and their loved ones, more than 2,000 members come together to ask questions, give advice, and share their stories with others who understand life with SMA.

Are you or your child living with SMA? Have you found any therapies that support healthy breathing? Share your experience in the comments below, or start a conversation by posting on your Activities page.

Posted on May 16, 2023
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Dennrik Abrahan, M.D. received his medical degree from the University of Central Florida. Learn more about him here.
Emily Wagner, M.S. holds a Master of Science in biomedical sciences with a focus in pharmacology. She is passionate about immunology, cancer biology, and molecular biology. Learn more about her here.

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