Spinal muscular atrophy is an inherited disorder that causes muscle weakness. It mostly affects children and can cause life-threatening symptoms.
What is spinal muscular atrophy?
Spinal muscular atrophy (SMA) is a group of inherited neuromuscular diseases that cause muscle weakness and can result in life-threatening symptoms. The disorder mostly affects babies and children.
In SMA, the issue is caused by a problem with the person’s genes not producing a specific protein that is important for the survival and proper functioning of the motor neurons (specialized nerve cells in the brain). When these motor neurons are unhealthy or die, they can no longer send signals to the muscles. This communication breakdown is why muscles become weak and waste away when a person has SMA.
AHN Neuromuscular Program
The AHN Neuromuscular Program, which is an integral part of AHN Neuroscience, is dedicated to serving patients with diseases of the peripheral nerves, neuromuscular junction, and muscles, including spinal muscular atrophy.[BH1.1] Our expert staff has decades’ worth of experience in treating these conditions and are certified by both the American Board of Clinical Neurophysiology and the American Association of Electrodiagnostic Medicine. This dual certification illustrates the exceptional quality of care our staff provide and their dedication to performing at the highest standards of practice in clinical neurophysiology and electrodiagnostic medicine.
Working primarily at Allegheny General Hospital, we see a broad range of patients who are navigating neuromuscular conditions and are skilled in guiding you through spinal muscular atrophy diagnosis and treatment.
Why choose AHN for your spinal muscular atrophy
At AHN, our physicians have specialized training in diagnosing and treating this complex neuromuscular disorder. Any condition affecting your child can cause stress and concern. We’re here to help reduce these worries, support you and your child, provide a precise diagnosis, and use the most effective therapies available.
Spinal muscular atrophy symptoms and signs
Spinal muscular atrophy symptoms and signs can often change depending on the age of the patient. There are some symptoms that spinal muscular atrophy causes for both children and adults, including:
- Muscle weakness: This is the main symptom. It can range from mild to severe, affecting muscles throughout the body. It often impacts the muscles closest to the center of the body (proximal muscles) more than those further out (distal muscles), like the hips and shoulders.
- Difficulty with movement: Caused by the muscle weakness, these symptoms can include trouble sitting up, crawling, or walking, difficulty lifting arms and legs, and problems with head control.
- Breathing difficulties: SMA can affect the muscles involved in breathing, leading to shallow breathing, frequent respiratory infections, or the need for breathing assistance.
- Feeding and swallowing difficulties: Muscles in the mouth and throat can be weak, making it hard to suck, swallow, and chew safely. This can lead to choking or aspiration (food/liquid going into the lungs).
- Scoliosis: Curvature of the spine often develops as the back muscles weaken and are unable to support the spine properly.
Causes and risk factors
The primary cause of spinal muscular atrophy (SMA) is a genetic mutation (a change in the DNA) in a specific gene called the Survival Motor Neuron 1 (SMN1) gene. The risk of developing SMA is having parents who are both carriers of the faulty SMN1 gene. This is why a family history of SMA can be important, as it might suggest that family members could be carriers.
SMA is purely genetic. It's not caused by anything you or your parents did or didn't do during pregnancy, nor by anything in the environment. Genetic testing can identify if someone is a carrier.
Spinal muscular atrophy screening and diagnosis
At AHN, our physicians use a comprehensive approach with the latest tests to pinpoint an accurate SMA diagnosis. Early and accurate diagnosis is crucial for starting treatment as soon as possible, which can significantly improve outcomes. If a child or adult starts showing signs of muscle weakness or other symptoms that doctors suspect might be SMA, we will perform specific diagnostic tests.
Electromyogram (EMG) for spinal muscular atrophy diagnosis
This test measures the electrical activity of your muscles. It helps doctors see if the muscle weakness is coming from the muscle itself or the nerves controlling it. In SMA, the EMG typically shows signs of nerve damage rather than primary muscle disease, which points toward a motor neuron disorder.
Nerve conduction studies for spinal muscular atrophy diagnosis
A nerve conduction velocity test measures the nerves’ ability to send electrical signals. We often perform it along with an EMG to help determine whether symptoms are related to nerves or muscles. In SMA, nerve conduction studies usually show normal or nearly normal nerve speed, but the response of the muscle to the nerve signal might be reduced. This helps to confirm that the issue is with the motor neurons and not the nerve itself.
Blood tests for spinal muscular atrophy diagnosis
Standard blood tests can look for other markers that might suggest muscle damage or rule out other conditions. For example, a creatine kinase level, which measures an enzyme in the body, might be slightly elevated in some muscle diseases. In SMA, it's typically normal or only mildly increased. This helps distinguish SMA from other muscle disorders.
Genetic tests
These are the most important tests for SMA. They look directly for the specific genetic mutations in the Survival Motor Neuron 1 (SMN1) gene that cause SMA. A positive genetic test definitively confirms an SMA diagnosis. It can also identify the specific type of SMA based on the number of SMN2 gene copies, which can influence severity.
Muscle biopsy
This test involves a physician removing a tiny piece of muscle for further analysis in a laboratory. This is a minor surgical procedure that is usually done under local anesthesia. While less frequently needed now because of advances in genetic testing, a muscle biopsy can show characteristic changes of muscle atrophy (wasting) due to nerve problems, further supporting an SMA diagnosis. It's often used when genetic test results are unclear or to rule out other conditions.
Types and stages of spinal muscular atrophy
Spinal muscular atrophy (SMA) is not a single condition. It is a spectrum of diseases, with different types of SMA affecting people of various ages with varying degrees of severity. Doctors often classify SMA based on when symptoms first appear and how much physical movement and mobility a person is able to achieve. Here are the main types of SMA.
Spinal muscular atrophy Type 1 (SMA Type 1)
Also known as Werdnig-Hoffmann disease, this is the most severe and common type and makes up about 60% of all SMA cases.¹ This condition is noticeable soon after birth or within the first few months of a baby’s life, often before 6 months of age. Babies with spinal muscular atrophy type 1 (or SMA type 1) experience profound muscle weakness, difficulty breathing and swallowing, and typically never learn to sit without support. Life expectancy without treatment is severely limited.
Spinal muscular atrophy Type 2 (SMA Type 2)
This intermediate form usually begins when a child is between 6 and 18 months of age, though symptoms can appear later. Children with spinal muscular atrophy type 2 (or SMA type 2) can typically sit independently but often cannot stand or walk on their own. They experience progressive muscle weakness, which may affect their legs more than their arms, and often develop scoliosis. Breathing difficulties can also become a concern.
Spinal muscular atrophy Type 3 (SMA Type 3)
Also called Kugelberg-Welander disease, this milder type of SMA has a later onset, with symptoms generally appearing between ages 2 and 17. Individuals with spinal muscular atrophy type 3 (or SMA type 3) initially have the ability to stand and walk independently, but they may later experience increasing muscle weakness, leading to difficulties with stairs and running. Eventually, SMA type 3 may cause the potential loss of walking ability over time.
Spinal muscular atrophy Type 4 (SMA Type 4)
This is the adult-onset form of SMA. Symptoms often do not show up until middle age, typically after 30 years old. Spinal muscular atrophy type 4 (or SMA type 4) is characterized by mild to moderate muscle weakness, primarily affecting the muscles closest to the body's center (proximal muscles). Progression is slow, and most individuals remain able to walk and maintain a normal life expectancy, though they may experience some mobility challenges.
Spinal muscular atrophy treatment
We understand the impact spinal muscular atrophy can have on your child’s life. Our specialists work with you to tailor spinal muscular atrophy treatment plan to your child’s needs. This collaborative approach provides a high level of personalized care.Treatment options include:
- Medication: We help determine which medications would offer the best results.
- Physical therapy: Certain exercises or activities may strengthen muscles so it’s easier to complete daily activities. Our knowledgeable, caring physical therapists customize a physical therapy plan to each patient’s needs.
- Orthopaedic devices: Devices such as braces offer support in everyday movements and help prevent injuries.
Spinal muscular atrophy FAQs
Any disease affecting a child is scary. AHN is here to help you navigate and find treatment for spinal muscular atrophy. Your dedicated care team is available to answer all your SMA questions and help you feel equipped with resources and solutions. We have answers to frequently asked questions that can help you get a basic understanding of the disease. You can use them to start conversations with your care team about your SMA diagnosis.
What is SMA disease?
Spinal muscular atrophy (SMA) is a genetic disease that affects the nerves responsible for controlling voluntary muscle movement, such as walking, breathing, and swallowing. It occurs when a specific gene (SMN1) doesn't work correctly, leading to a shortage of a vital protein needed by these nerves. Without this protein, the nerves weaken and die, causing muscles to become weak and waste away over time. SMA can vary greatly in severity, from very severe in infants to milder forms that appear in adulthood.
How common is spinal muscular atrophy?
Spinal muscular atrophy is considered a relatively rare genetic disease. It affects approximately 1 in every 10,000 live births worldwide.¹ While the disease itself is rare, a significant number of people are carriers of the gene. About 1 in 50 people in the general population carry one copy of the gene that causes SMA, meaning they don't have the disease but can pass it on to their children.
What causes spinal muscular atrophy?
A problem with a specific gene called SMN1 causes spinal muscle atrophy. This gene is responsible for producing a protein essential for the health of motor neurons — the nerve cells that tell your muscles when to move. In almost all cases of SMA, individuals inherit two faulty copies of this SMN1 gene, one from each parent. When there isn't enough of the crucial SMN protein, these motor neurons can't function properly and begin to die off, leading to muscle weakness. SMA is a genetic condition; it is not caused by environmental factors, lifestyle, or anything that happened during pregnancy.
Contact us
To schedule an appointment or learn more about AHN Neuroscience services, please call 412-359-8850 if you live in the Pittsburgh area. If you live in the Erie region, please call 814-452-7575.