What is Spinal Muscular Atrophy (SMA)? Let's talk about this rare condition in simple terms

Have you ever felt like your little one is a little lethargic, or less active than other children? Maybe your child has difficulty holding their neck properly, or their body feels like it's loose? It's normal for a parent or a parent to feel scared when they see something like this. Today we're going to talk about a rare condition that can cause these symptoms, but isn't talked about much in society. That's Spinal Muscular Atrophy, or SMA for short. Don't be scared when you hear this name. In this article, we'll talk about this disease simply, in a way that you can understand.

What exactly is SMA?

Simply put, Spinal Muscular Atrophy (SMA) is a genetic (inherited) condition. It is a disease related to the nervous system. Due to this disease, some of the muscles in our body gradually weaken and atrophy. Just like an unused tool gradually rusts.

Let's explain this a little more. Our brain and spinal cord send messages to the muscles in our body telling them to move. These messages are carried by a special type of nerve cell that acts like an electrical wire. We call these lower motor neurons . What happens in SMA is that these motor neurons are gradually destroyed. Then the message from the brain to the muscles to "move" is not received properly. When the message is not received, the muscles become inactive and gradually weaken.

In this disease, the muscles closest to the center of the body (proximal muscles) are particularly weakened. For example, areas such as the shoulders, hips, and thighs. The muscles farther from the center of the body (distal muscles), such as the fingertips, are less affected. This weakness increases over time.

What are the main types of SMA?

SMA is not all the same. Doctors divide it into five main types based on the age at which symptoms begin, the severity of the disease, and the lifespan. Understanding this classification can help you better understand the disease.

Why does this SMA disease occur? What is the cause?

As we said before, this is a genetic disease. That means it is caused by a defect in our genes.

There is a gene in our body called SMN1 (Survivor Motor Neuron 1) . The main function of this gene is to produce a protein (SMN protein) that is essential for the survival of motor neurons that we talked about earlier. A person with SMA has a mutation or defect in this SMN1 gene. Therefore, the body does not produce enough SMN protein. Without this protein, motor neurons cannot survive. They gradually shrink and die.

So what is the SMN2 gene?

Fortunately, our body has another gene similar to the SMN1 gene. That's the SMN2 gene. This is like a 'backup' of the SMN1 gene. However, this SMN2 gene only produces a very small amount of SMN protein.

The severity of the disease is determined by the number of copies of the SMN2 gene. The more copies of the SMN2 gene a person has, the more SMN protein the body produces. Therefore, even if the SMN1 gene is inactive, the deficiency can be compensated for to some extent. Therefore, the symptoms of those with more copies of SMN2 are milder.

How is this disease inherited by a child?

This is inherited in an autosomal recessive pattern. This means that for a child to develop this disease, both the mother and father must inherit the defective SMN1 gene.

Often, both parents are "carriers" - carrying one copy of the defective gene. But they don't have any symptoms because they have one good SMN1 gene. When two such carrier parents have a child,

• There is a 25% chance that the child will develop the disease.
• There is a 50% chance that the child will also be a carrier.
• The baby has a 25% chance of being healthy without any defects.

How is SMA diagnosed?

If your child is suspected of having SMA, the doctor will first ask you about your child's symptoms and family medical history. Then they will perform a physical and neurological examination.

The main test to confirm the presence of SMA is genetic testing. This is a simple blood test. It can accurately diagnose SMA 95% of the time. In developed countries, all newborns are now tested for this disease.

Sometimes the symptoms of SMA can be similar to other neuromuscular diseases, such as muscular dystrophy. So if your doctor doesn't immediately suspect SMA, they may order other tests to find the cause, such as:

• Creatine Kinase (CK) blood test: This enzyme builds up in the blood when muscles are damaged. However, CK levels are not usually elevated in SMA.
• Electromyogram (EMG) and Nerve Conduction Study: These tests measure the electrical activity of muscles and nerves.
• Muscle Biopsy: This is not done very often anymore. Here, a small piece of muscle is taken and examined.

Can this be detected during pregnancy?

Yes. If someone in your family has SMA, you can test your unborn baby for the disease during pregnancy. There are two main tests:

1. Amniocentesis: In this procedure, a small amount of the amniotic fluid surrounding the baby in the womb is removed with a syringe and subjected to genetic testing.

2. Chorionic Villus Sampling (CVS): Here, a small piece of tissue is taken from the placenta and examined.

What are the treatments for SMA?

Unfortunately, there is no cure for SMA yet. But don't worry. There are many things you can do to control symptoms, prevent complications, and make your child's life easier. In addition, there have been some very effective drugs recently discovered that can change the course of the disease.

Treatment can be divided into two main parts:

1. Symptom management and supportive care

These are designed to reduce the discomfort caused by the disease and help the child live the best possible life.

• Physical therapy: Helps maintain correct posture, prevent joint stiffness, and slow muscle weakness.
• Occupational therapy: Helps the child to perform daily tasks independently.
• Assistive devices: You may need to use various aids, such as braces, crutches, walkers, and wheelchairs.
• Speech and swallowing therapy: Helps with speech and swallowing difficulties.
• Feeding tube: If swallowing is too difficult or dangerous, a tube may be inserted through the nose or stomach directly into the stomach.
• Assisted ventilation: When breathing difficulties occur, special machines (ventilators) must be used.

2. Medications that modify the course of the disease

Since 2016, several drugs have been introduced that have revolutionized the treatment of SMA. These can significantly change the course of the disease.

• Disease-Modifying Therapy: These drugs work by stimulating the 'backup' gene we talked about earlier, the SMN2 gene, and causing it to produce more SMN protein. Nusinersen (Spinraza®) and Risdiplam (Evrysdi®) are this type of drug.
• Gene Replacement Therapy: This is a very advanced treatment. The drug onasemnogene abeparvovec-xioi (Zolgensma®) replaces the missing or defective SMN1 gene with a functioning SMN1 gene. This is a one-time treatment given intravenously (IV).

Progression of SMA disease and possible complications

Over time, muscle weakness can lead to various complications.

• Scoliosis , hip dislocation, fractures.
• Malnutrition and dehydration due to difficulty swallowing food.
• Chest infections such as aspiration pneumonia caused by food entering the airway.
• Lung weakness and difficulty breathing.

The life expectancy of a child with SMA varies greatly depending on the type of disease. In types 3 and 4, life expectancy is usually not significantly affected. In more severe cases like type 1, the challenges are greater. However, with newly introduced treatments, the life expectancy and quality of life, especially for type 1 children, has now increased significantly. Therefore, the best person to know the most accurate information about your child's condition is your doctor.

Spinal Muscular Atrophy, SMA, muscle weakness, genetic diseases, children's diseases, neurological diseases, SMN1 gene, Werdnig-Hoffman disease