What is SMA (Spinal Muscular Atrophy)? Symptoms, Causes and Treatment
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What is SMA?
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What Causes SMA?
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SMA Test
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Frequently Asked Questions
Spinal Muscular Atrophy (SMA) is a genetic neuromuscular disease. SMA occurs as a result of damage and eventual loss of motor neurons (nerve cells that control muscle movements) in the body, leading to muscle weakness and atrophy (muscle wasting). This condition severely affects mobility.
What is SMA?
Spinal Muscular Atrophy (SMA) is a genetic neuromuscular disease that affects the motor neurons in the spinal cord. These neurons are responsible for controlling muscle movements. In SMA, the loss of motor neurons leads to progressive muscle weakness and atrophy (muscle mass reduction). The cause of SMA is a defect in the SMN1 gene, which is responsible for producing the SMN protein essential for the survival of motor neurons. In individuals with SMA, the SMN1 gene is either absent or mutated, leading to insufficient amounts of functional SMN protein. SMA has different types, which vary depending on the severity of symptoms and the age at which they begin. Symptoms of SMA include muscle weakness, muscle atrophy, movement problems, respiratory and swallowing difficulties, and developmental delays.
What Causes SMA?
Spinal Muscular Atrophy (SMA) arises from a genetic disorder. The fundamental cause of this disease is a problem in the "survival motor neuron 1" (SMN1) gene. This gene is responsible for producing a protein that is critical for the health of motor neurons in the body. Motor neurons are the nerve cells that send signals from the brain and spinal cord to the muscles, enabling movement.
In individuals with SMA, a mutation or deficiency occurs in the SMN1 gene, which prevents the production of sufficient amounts of the SMN protein. The lack of SMN protein leads to damage and loss of function in the motor neurons. As a result, muscles weaken and atrophy.
SMA is inherited in an autosomal recessive manner. This means that the disease occurs only if both parents carry a mutated SMN1 gene. If only one parent is a carrier, the child will not have SMA but will carry the risk of being a carrier.
In summary, the primary cause of SMA is the inability to produce enough SMN protein due to a problem in the SMN1 gene. This leads to damage to motor neurons and muscle weakness. SMA is a genetic disease that is present at birth and follows a progressive course.
Types of SMA
SMA is caused by a mutation or deficiency in the SMN1 gene. This gene produces the SMN protein, which is necessary for the survival of motor neurons. A deficiency of the SMN protein causes damage to the motor neurons and muscle weakness.
SMA is divided into different types based on the age of onset and severity of symptoms:
- Type 1 (Werdnig-Hoffman Disease): The most severe and common form. Symptoms appear at birth or within the first few months. Babies are unable to achieve basic motor skills such as holding their head up, sitting, and walking. Respiratory and swallowing difficulties are common. Without treatment, it is usually life-threatening by the age of 2.
- Type 2: A moderately severe form. Symptoms appear between 6-18 months. Children can sit but are unable to walk. Respiratory problems and scoliosis (spinal curvature) may develop.
- Type 3 (Kugelberg-Welander Disease): A milder form. Symptoms appear after 18 months. Children can walk but may gradually lose this ability. Muscle weakness and fatigue are common.
- Type 4: The mildest form. Symptoms appear in adulthood. Muscle weakness and slowly progressing movement limitations occur.
Symptoms of SMA
The symptoms of SMA can vary depending on the type and severity of the disease. However, certain symptoms are commonly seen in individuals with SMA. The main symptoms of SMA include:
- Muscle Weakness and Atrophy: The most noticeable symptom of SMA is muscle weakness, which typically begins in the central parts of the body (spine, hips) and progresses to the limbs. Muscle weakness eventually leads to muscle atrophy (shrinkage). Infants may have difficulty with head control, sitting, crawling, and walking, showing delays in motor skills. Older children and adults may experience difficulty walking, climbing stairs, and carrying objects.
- Movement Problems: Muscle weakness and atrophy can affect coordination and balance. Individuals with SMA may experience tremors, balance issues, and frequent falls. In advanced stages, mobility may be severely limited, and the use of a wheelchair may be necessary.
- Respiratory Problems: SMA can also affect the respiratory muscles. Infants and young children may experience difficulty breathing, frequent infections, and trouble coughing. In later stages, respiratory failure can develop, requiring ventilator support.
- Swallowing and Feeding Problems: SMA can affect the muscles used for swallowing. Infants may have difficulty sucking and swallowing, leading to feeding problems. Older children and adults may have difficulty swallowing, leading to prolonged meal times and inadequate nutrition.
Other Symptoms:
- Scoliosis (spinal curvature)
- Joint contractures (joint stiffness)
- Reduced or absent reflexes
- Fatigue
How is SMA Diagnosed?
Spinal Muscular Atrophy (SMA) is diagnosed through a combination of symptoms, clinical evaluation, and genetic testing, as it is a genetic disease. Accurate diagnosis of SMA is crucial to determine the type of the disease and begin appropriate treatment. The main steps in diagnosing SMA include:
Clinical Evaluation:
- Medical History: The doctor will inquire about the patient’s symptoms, when they began, how they have progressed, and if there is a family history of SMA.
- Physical Examination: The doctor will assess the patient’s muscle strength, reflexes, mobility, and other neurological signs.
Neurological Examination:
- Neurological functions such as motor skills, reflexes, sensation, and coordination are thoroughly examined.
- Muscle weakness and atrophy (muscle loss) are evaluated.
Electromyography (EMG): EMG measures the electrical activity of muscles. In SMA patients, muscle electrical activity decreases due to motor neuron loss. EMG can support the diagnosis of SMA and help differentiate it from other neuromuscular disorders.
Genetic Testing: The definitive diagnosis of SMA is made through genetic testing. Genetic tests look for mutations or deletions in the SMN1 gene. About 95% of individuals with SMA have a mutation or deletion in the SMN1 gene.
Muscle Biopsy (if necessary): A muscle biopsy involves taking a small sample of muscle tissue and examining it under a microscope. Although SMA is typically diagnosed with genetic testing, in some cases, a muscle biopsy may be performed to differentiate SMA from other muscle diseases.
Other Tests (if necessary):
- Creatine Kinase (CK) Test: CK levels may be elevated in cases of muscle damage.
- Lung Function Tests: These can assess if respiratory muscles are affected.
SMA Test
The SMA test is a type of genetic test used to determine the risk of having this genetic disorder. SMA is a rare but serious genetic disease that causes muscle weakness and progressive neuromuscular degeneration. The SMA test helps to determine whether an individual carries the genetic mutation that causes SMA.
Why is the SMA Test Done?
There are several important reasons to undergo an SMA test:
- Carrier Detection: The SMA test is done to determine whether an individual carries the mutation that causes SMA. If a person is a carrier, they may not have SMA themselves, but they could pass the mutation to their child.
- Diagnosis: The SMA test is also used to diagnose individuals who show symptoms of SMA.
- Risk Assessment: It can be performed to assess the risk of carrying the SMA gene in individuals with a family history of SMA.
- Pre-Marital Counseling: Couples who are considering marriage can undergo carrier testing to assess the risk of having a child with SMA.
- Prenatal Diagnosis: During pregnancy, prenatal testing can be done to determine whether the baby has SMA.
How is the SMA Test Performed?
The SMA test is usually done with a simple blood sample. The blood sample is sent to a laboratory, where genetic analysis is performed to investigate mutations in the SMN1 gene. Test results may take several weeks to be available.
What Do SMA Test Results Mean?
The results of the SMA test can be one of three outcomes:
- Negative: This means that the person does not carry the mutation that causes SMA.
- Positive: This means that the person carries the mutation that causes SMA. Carrier individuals do not have SMA themselves but have a risk of passing the mutation to their children.
- Unclear: In some cases, test results may be inconclusive, and further testing may be required.
Who Should Consider Taking the SMA Test?
You might consider taking the SMA test if:
- There is a family history of SMA.
- You are showing symptoms of SMA.
- You are considering marriage and want to understand the risk of SMA.
- You are pregnant and want to know if your baby is at risk for SMA.
How is SMA Treated?
Treatment for Spinal Muscular Atrophy (SMA) has made significant progress in recent years. Various treatment methods are available to slow the progression of the disease and improve the quality of life. SMA treatment requires a multidisciplinary approach and is typically applied through a combination of the following methods:
Gene Therapy:
- Onasemnogene abeparvovec (Zolgensma): This treatment targets the genetic defect causing SMA. A healthy copy of the SMN1 gene is delivered to the body via a virus. It can be highly effective, especially when administered at an early age.
Splicing Modifier Treatment:
- Nusinersen (Spinraza): This drug increases the ability of the SMN2 gene to produce the SMN protein. It is injected into the spinal cord and needs to be repeated at regular intervals.
SMN Protein Production Enhancement:
- Risdiplam (Evrysdi): This medication increases the production of the SMN protein. It can be taken orally, making it easier to use.
4.Supportive Therapies:
- Physical Therapy and Rehabilitation: Important for maintaining muscle strength, joint range of motion, and improving motor skills.
- Respiratory Support: Patients with affected respiratory muscles may require ventilatory support.
- Nutritional Support: In patients with difficulty swallowing, a feeding tube may be necessary.
- Orthopedic Support: Treatment may be needed for orthopedic issues, such as scoliosis.
- Speech Therapy: Useful for patients with speech and communication difficulties.
- Psychological Support: Important for coping with the emotional impact of the disease.
Choosing Treatment:
SMA treatment is determined based on the patient's age, the type and severity of the disease, symptoms, and overall health status. The decision regarding treatment is made collaboratively between the patient’s family and the doctor.
Frequently Asked Questions
Is SMA Hereditary?
SMA (Spinal Muscular Atrophy) is hereditary. SMA is inherited in an autosomal recessive manner. This means that both parents must be carriers of the SMN1 gene mutation. Carriers of the disease do not develop SMA themselves, but they have a risk of passing the carrier status to their children. Therefore, if both parents are carriers, there is a risk that their child may develop SMA.
At What Age Does SMA Begin?
The onset of SMA depends on the type of the disease:
- SMA Type 1: Starts within the first 6 months after birth and is usually life-threatening.
- SMA Type 2: Starts between 6-18 months and shows weakness in motor skills. It progresses slowly.
- SMA Type 3: Starts after the 18th month, mostly during childhood, and usually progresses more slowly.
- SMA Type 4: Starts in adulthood, typically around the age of 30, and generally progresses more slowly.
What is SMA Carrier Status?
SMA carrier status is determined by the presence of a single copy of the mutation in the SMN1 gene. In this case, the person does not develop the disease but carries the genetic trait that could be passed on to their children. SMA carriers are individuals who carry the genetic change that causes the disease but do not show any symptoms. There is a risk that children of two carrier parents may develop SMA.
Can SMA Be Prevented?
Since SMA is a genetic disease, it is not currently possible to prevent it entirely. However, genetic testing and carrier screening can identify carriers, and families can be made aware of the risks. Newborn screening can help with early diagnosis of SMA, and treatment can be started quickly to slow down the effects of the disease. Other than this, there is no treatment or preventive method to stop the onset of SMA.
Does Consanguinity Cause SMA?
Consanguineous marriage may increase the risk of SMA. In consanguineous marriages, there is a higher likelihood of carrying the same genetic defects. If both parents are carriers of the gene that causes SMA, there is a 25% risk that their child may develop SMA. Consanguineous marriage increases this likelihood because individuals in such marriages are more likely to have the same genetic defects.
* Contents of this page is for informational purposes only. Please consult your doctor for diagnosis and treatment. The content of this page does not include information on medicinal health care at Liv Hospital .
