Spinal muscular atrophy (SMA) affects many body systems and not just the muscular system. Some of these effects can appear before signs of muscular weakness, which suggests that they are not simply a consequence of SMA’s effect on our muscles.

The muscular atrophy caused by SMA can also directly affect other systems:

• Weakened breathing muscles cause respiratory difficulty.
• Weakened chewing and swallowing muscles lead to feeding problems.
• Spinal muscle weakness leads to spine curvatures like scoliosis or kyphosis.

Complications that are not directly related to muscle weakness are less well understood. However, research suggests a connection between SMA and many other conditions. Genetic research has found that survival motor neuron (SMN) deficiency can affect all cells, not just the motor neurons.

Cardiac Complications

One study from 2019 was based on researching simultaneous disorders in people with SMA before their first signs of skeletal muscular weakness. The researchers tried to exclude the possibility that the conditions were caused by the muscular degeneration that's commonly associated with SMA.

This study, based on researching insurance claim data from those who were later diagnosed with SMA, found a variety of cardiac complications among those with the condition, including:

• Cardiomyopathies (dysfunction in the muscle tissue of the heart)
• Shunting and septal defects (holes between the chambers of the heart)
• Valve disorders
• Arrhythmias (premature heartbeats)

Interestingly, studies have shown that mice treated with therapeutic drugs that increase SMN have shown improvement in cardiac deficiencies. Although the link between SMA and cardiac complications seems clear, more research is needed to understand the mechanisms involved.

Vascular Insufficiency

Chronic venous insufficiency and peripheral vascular disease have been linked to SMA. These conditions describe poor blood circulation. This has been shown in studies involving humans and mice alike. The effects of vascular disease in mice appear to be more severe, including necrosis (death) of muscle at the tips of ears and tails. This finding might seem to be an effect of muscle degeneration, but it is more accurately described as being caused by poor circulation.

Vascular disease in humans can lead to pain or numbness in the hands and feet, or slow wound healing anywhere on the body. If you have SMA and are experiencing either of these conditions, consider asking your primary care provider if you might have vascular insufficiency.

Gastrointestinal Disorders

Many gastrointestinal disorders appear to be linked with SMA in humans:

• Persistent vomiting
• Gastroesophageal reflux disease and reflux esophagitis
• Congenital defects of the digestive system
• Intestinal obstruction
• Dysphagia (difficulty swallowing)
• Constipation

Although it can be argued that dysphagia and constipation could be linked to early muscle weakness, the other disorders are likely not related. More studies are necessary to fully understand (and prove) the link between SMA and these conditions. For now, we know that people with SMA experience these conditions at a higher rate than the general population.

Metabolic Conditions (Pancreas and Liver Involvement)

Our understanding of how nutrition affects the body is still limited. A relatively new field of study, metabolomics, is currently attempting to broaden what researchers know about nutrition, metabolism, and the relevant body systems.

Right now, scientists don’t know enough how SMA can affect metabolism. However, many studies suggest a link between SMA and certain liver and pancreatic problems, which can lead to poor body fat and blood sugar regulation. A study from 2020 states that studies involving mice and infants have shown pancreatic developmental deficiencies, which can lead to poor glucose regulation. Liver dysfunction has also been found in both human and mouse studies, involving several of the over 500 essential functions our livers perform. Liver dysfunction can lead to multiple difficulties with metabolizing and using nutrition properly, including increased body fat and cholesterol. Studies have not yet shown why people experiencing SMA may be vulnerable to these conditions.

Reproductive Complications

Dysfunction of the male reproductive system has been found in both human and mouse studies. Some mice with SMA have been born infertile, and some men with SMA are infertile or have testicular hypofunction, which can lead to decreased testosterone or sperm production.

Neuromuscular disease used to be a reason some providers would discourage pregnancy. Fortunately, a recent study has found that most people with SMA enjoyed their pregnancies and that many had favorable and healthy outcomes. People with severe spinal curvatures and markedly decreased breathing capacities had the most difficult birthing processes. However, with respiratory support technology improving, those experiencing breathing difficulties have also successfully given birth to healthy babies.

Skeletal and Brain Abnormalities

Science has not yet made a connection between skeletal or brain abnormalities and humans living with SMA. Signs of osteoporosis have been discovered in mice with SMA. However, studies involving data from humans have yet to show an increased risk of osteoporosis for those living with SMA. Although mouse studies reveal some brain development abnormalities, thankfully, people with SMA have been proven to have healthy cognitive function throughout their lifespans.

In summary, more research is needed to understand the connection between SMA and various health conditions. However, growing evidence indicates that SMA is a multisystem disorder, as opposed to a disorder of muscle only. This finding is important because more research confirming these linkages and why they happen will help primary care providers and specialists screen for and prevent complications before they become severe.

Talk With Others Who Understand

On mySMAteam, the social network for people with spinal muscular atrophy, more than 1,300 members come together to ask questions, give advice, and share their stories with others who understand life with SMA.

Have you experienced any of the conditions discussed in this article? Share your experience in the comments below, or start a conversation by posting on your Activities page.