Spinal muscular atrophy (SMA) is a neuromuscular disorder that causes muscle weakness. SMA’s impact on physical function, quality of life, and life expectancy is different in everyone. The type of SMA and age at diagnosis are two key factors that predict how severe the symptoms will be. Starting treatment with disease-modifying treatments early improves outcomes. Disease-modifying treatments change the course of the disease rather than just easing symptoms.

Some people with SMA use a wheelchair and need help with daily tasks like bathing, dressing, and eating. Others can walk and do most activities of daily living on their own. Knowing what to look out for can help you research the right type of support.

1. Muscle Weakness

Muscle weakness, or a lack of muscle tone, is called hypotonia. It’s the main symptom of all types of SMA. Muscle weakness in SMA is caused by the loss of nerve cells responsible for communication between the brain and the muscles.

Most people with SMA have types 0 to 4. These types are all caused by a mutation (change) in the survival motor neuron 1 (SMN1) gene. Another gene, SMN2, determines which type of SMA a person develops. The types of SMA were established before SMA treatment became available. Early treatment improves symptoms and outcomes.

In SMA, weakness usually affects the muscles near the shoulders and hips, called proximal muscles. It often starts in the lower body and occurs on both sides. Over time, this weakness can slow motor skill development and cause problems with walking, swallowing, breathing, and mobility.

Muscle weakness is most severe in type 0 and type 1 (also known as Werdnig-Hoffmann disease), the most serious forms of SMA. Without treatment, babies with types 0 and 1 have no head control and do not reach developmental milestones. Severe muscle weakness affects their breathing ability and their life expectancy.

In types 0 and 1, muscle weakness comes with severely reduced muscle reflexes. Lack of muscle reflexes is also common among those with type 2.

2. Mobility Limitations

SMA can cause mobility problems that range from not being able to lift the head or sit without support to mild difficulties walking.

Sucking, Chewing, and Swallowing

Problems with sucking and swallowing in babies with severe SMA are caused by weak muscles in the throat and mouth. Infants who have trouble sucking and swallowing may not get the nutrition they need. This difficulty can also cause problems such as inhaling food or liquid into the lungs. Older babies and toddlers with severe SMA may also struggle with chewing. Infants and children with SMA may need a feeding tube to receive enough nutrition.

Sitting Up

Without treatment, infants and children with SMA types 0 and 1 are never able to sit up by themselves. Babies and toddlers with SMA type 2 will develop the muscle strength to sit up without help. However, those with type 2 may lose the ability to sit up by themselves by their midteen years.

Standing

Before treatment was available, children with SMA type 2 typically could sit but rarely stood or walked without help. Those with type 3 (Kugelberg-Welander disease) are usually able to stand. Without treatment, some children with type 3 may slowly lose the ability to stand, while others may struggle to move from sitting to standing.

Walking

Without early treatment, babies and children with types 0 to 2 will never develop the ability to walk. Depending on the age at diagnosis, young children with type 3 generally learn to walk but may start falling or having difficulty with stairs around 2 to 3 years old. People with type 3 may also have problems with falling and stairs as SMA progresses and muscles weaken. They may develop foot deformities or abnormal walking patterns that can make walking more challenging. Adults with type 4 may also develop walking problems as they age and SMA progresses.

SMA with lower extremity predominance (SMA-LED) is one of the rarest forms of the disease. It also causes trouble walking because of muscle weakness in the legs, especially the thighs.

3. Breathing Issues

Problems with breathing can be the most dangerous aspect of SMA. These problems are caused by weak respiratory muscles. Complications related to breathing may reduce life expectancy, especially in the more severe types of SMA. However, once again, note that early treatment improves symptoms and helps people with SMA live longer.

Breathing

A person without SMA breathes using their diaphragm and intercostal muscles. The intercostal muscles cause the chest to expand and contract when breathing. The diaphragm is a separate muscle that moves the rib cage up and down. SMA can cause weakness in the intercostal muscles. This happens mostly in types 0 to 2 and rarely in type 3. The diaphragm is forced to compensate for or make up for weak intercostal muscles. This leads to abnormal breathing patterns and underdeveloped lungs.

Breathing problems can also be related to scoliosis (curvature of the spine). It’s a very common complication of SMA type 2. The changed shape of the spine can reduce the capacity or available space in the lungs. Those with respiratory weakness will require respiratory care to support breathing.

Sleep problems are common in children with types 1 and 2 because of weak breathing muscles. These weak muscles can make breathing during sleep too slow or too shallow, so people with SMA may not take in enough oxygen or release enough carbon dioxide. This can cause headaches, but a mechanical breathing machine can provide support at night and, in some cases, during the day as well. If breathing becomes too difficult, a tracheostomy — a breathing tube placed in the neck — may be needed, with the machine connected to help with airflow.

Coughing

Weak respiratory muscles can make it hard for people with SMA to cough and clear their lungs, which makes breathing more difficult and raises the risk of chest infections. In some cases, this can even lead to complete or partial lung collapse. A cough machine uses air pressure to help push mucus out of the lungs. Manual cough assistance is when a caregiver presses on the chest or abdomen to help clear the lungs.

Infection

People with SMA have a higher risk of pneumonia and other chest infections. Respiratory infections are most common in SMA types 1 and 2 and in SMA forms that affect breathing. Mechanical cough machines and other treatments can help keep the lungs clear.

4. Musculoskeletal Symptoms

Scoliosis is when the spine curves to the side. Instead of the spine being held by muscles in a normal curve, the spine creates an “S” shape. Scoliosis affects many children with SMA type 2 and, less often, those with type 3. The change in spine shape is caused by muscle weakness. It can cause breathing problems and limited mobility. SMA-related scoliosis is often treated with surgery or bracing. People with SMA may also have kyphosis, a forward bend in the spine.

Joint contracture is a deformity caused by the shortening or tightening of muscles or tendons. Joint contractures in the lower limbs are more common in people with SMA than in the upper limbs. The hips and knees are the most affected areas. Physical therapy or surgery can help.

Hip weakness and dislocation can affect people with SMA, especially type 3. In some cases, surgery is recommended.

Bone fractures occur frequently in SMA types 2 and 3. Fractures in the thigh bone near the knee and in the ankle are common in type 2. Fractures in the arms are common in type 3. In some cases, infants born with SMA may be born with broken bones.

5. Mental Health Effects

Depression and mood disorders are common for people with chronic health conditions, including SMA. In a series of interviews with 19 young people with SMA, several reported depression or feelings of sadness related to their condition. If you’re experiencing symptoms of depression, speak to your healthcare provider. Treatment options, including therapy and medication, can help.

Depression can also affect the parents of babies and children with SMA. In-person or online support groups like mySMAteam can help you feel less alone. You may also want to get support from a mental health professional.

Other Symptoms of SMA

SMA comes with many different symptoms. No two people with SMA are exactly alike.

Sometimes the symptoms of SMA can be subtle. For example, it may become harder to climb the stairs, or you may notice occasional shakiness.

You should always contact your healthcare provider if you feel like something isn’t right with you or your child. With some investigation, you can find out what’s going on and figure out the best next steps. You can also ask about newer treatment options and whether there are any promising clinical trials you may be qualified to join.

Find Your Team

On mySMAteam, people talk about their experiences with spinal muscular atrophy, get advice, and find support from others who understand.

Have you had some of these symptoms of spinal muscular atrophy? Do you have any tips for managing them? Share your thoughts in the comments below.