Understanding Spinal Muscular Atrophy: Causes, Symptoms, and Treatment Options

Spinal Muscular Atrophy (SMA) is a rare genetic disorder affecting the motor neurons in the spinal cord, leading to muscle weakness and atrophy. Despite its low prevalence, SMA poses significant challenges to those diagnosed and their families.

This blog aims to shed light on the intricacies of SMA, including its causes, symptoms, available treatments, and ongoing research efforts to improve patient outcomes.

What is Spinal Muscular Atrophy?

An inherited neuromuscular condition known as spinal muscular atrophy (SMA). It weakens muscles as it targets motor neurons in the spinal cord, which control muscle movement. Without these neurons, muscles receive no signals for movement. This leads to muscle atrophy, where muscles shrink and weaken due to inactivity.

What are the Types of Spinal Muscular Atrophy? 

The four main forms of spinal muscular atrophy are as follows:

Type 1 (Severe)

• About 60% of people with SMA have type 1, also known as Werdnig-Hoffman disease.
• During the first six months of life or at birth, symptoms appear.
• Infants struggle with swallowing and sucking and fail to achieve typical milestones.
• Respiratory infections and collapsed lungs become prevalent as muscles weaken.
• Most children with type 1 SMA don’t survive beyond their second birthday.

Type 2 (Intermediate)

• Symptoms emerge between six to 18 months, termed Dubowitz disease.
• Lower limb weakness is characteristic; sitting up may be possible but not walking.
• Despite limitations, most individuals with type 2 SMA live into adulthood.

Type 3 (Mild)

• Also known as Kugelbert-Welander or juvenile-onset SMA.
• Symptoms arise after 18 months, sometimes not until early adulthood.
• Mild muscle weakness, difficulty walking, and respiratory infections are common.
• Progression may affect walking ability but doesn’t significantly impact life expectancy.

Type 4 (Adult)

• Rare form appearing in mid-30s with slow progression of muscle weakness.
• Afflicted individuals typically remain mobile and lead full lives.

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What are the Symptoms of Spinal Muscular Atrophy? 

Spinal Muscular Atrophy (SMA) presents varying symptoms, and severity depending on the age of onset:

In infants, symptoms are severe and potentially life-threatening, such as:

• Breathing Issues: weak lungs, coughing, shallow sleep breathing, shortness of breath.
• Feeding Problems: weak swallowing muscles, risk of choking or aspiration.
• Muscle Weakness: affects mobility, motor development, and poor neck, and head control.

SMA also includes:

• Scoliosis: The curvature of the spine, impacting posture, causing pain.
• Frequent Respiratory Infections: Pneumonia risk due to compromised breathing.
• SMA may involve multiple organs and, the immune system, heightening infection risk.

Management involves swallowing therapy, mobility aids, and possibly feeding tubes, to address symptoms and enhance quality of life.

What are the Causes of Spinal Muscular Atrophy?

SMA is caused by a deficiency in the SMN1 gene, leading to insufficient SMN protein production vital for motor neuron health. Without enough SMN protein, motor neurons deteriorate, impairing voluntary movement control, especially in the head, neck, arms, and legs.

Individuals possess SMN2 genes, which can partially compensate for SMN1 deficiency, with up to eight copies per person. More SMN2 copies often correlate with milder SMA symptoms due to increased SMN protein production.

Occasionally, SMA stems from mutations in genes other than SMN1 (non-chromosome 5), although this is rare.

How is Spinal Muscular Atrophy Diagnosed?

Some symptoms of Spinal Muscular Atrophy (SMA) mimic those seen in neuromuscular disorders such as muscular dystrophy. Healthcare providers conduct physical exams and review medical histories to ascertain the underlying cause of symptoms. The diagnostic tests for SMA are:

• Blood Test: Measures enzyme and protein levels, notably creatine kinase, indicating muscle deterioration.
• Genetic Test: Identifies abnormalities in the SMN1 gene, with a 95% accuracy rate in diagnosing SMA.
• Nerve Conduction Test: Utilises electromyogram (EMG) to assess nerve and muscle electrical activity.
• Muscle Biopsy: Rarely performed, it involves extracting muscle tissue for laboratory examination, revealing muscle atrophy.

The prenatal tests for SMA include:

• Amniocentesis: Conducted after the 14th week of pregnancy, involves extracting amniotic fluid for SMA analysis, slightly increasing miscarriage risk.
• Chorionic Villus Sampling (CVS): This can be done as early as the 10th week, and entails retrieving placental tissue for SMA examination via the cervix or abdomen.

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What is the Treatment for Spinal Muscular Atrophy?

SMA lacks a cure. Treatments vary based on SMA type and symptoms. Physical therapy, occupational therapy, and assistive devices like braces, crutches, walkers, and wheelchairs aid many SMA patients.

Disease-modifying therapy like Nusinersen stimulates SMN protein production, administered via spinal canal injection. Risdaplam, taken orally, aids adults and children older than two months.

Gene replacement therapy benefits infants under two through a one-time IV infusion of onasemnogene abeparvovec-xioi, replacing a faulty SMN1 gene with a functional one.

What are the Complications of Untreated Spinal Muscular Atrophy?

Throughout their condition, individuals with SMA undergo a gradual decline in muscle strength and coordination. This progression may lead to various complications, such as:

1. Fractures, dislocation of the hip, and scoliosis (abnormal curvature of the spine).
2. Challenges related to nutrition and hydration stemming from difficulties in eating and swallowing, potentially necessitating the use of a feeding tube.
3. Susceptibility to pneumonia and other respiratory infections.
4. Weakening of the lungs and respiratory issues that might necessitate assistance with breathing through ventilation support.

How can you Prevent Spinal Muscular Atrophy?

Inheritance of SMA is a genetic phenomenon. Should either you or your partner possess the mutated gene responsible for SMA, consulting a genetic counsellor can provide insights into the likelihood of your child inheriting SMA or becoming a carrier.

Before conception, steps can be taken to reduce the risk of passing on SMA. Preimplantation genetic diagnosis (PGD) identifies embryos without the mutated gene, ensuring that during in vitro fertilization (IVF), only healthy embryos are implanted. This method ensures that your child will inherit two healthy SMN1 genes, preventing SMA.

Conclusion

Spinal muscular atrophy poses significant challenges, but advancements in research, treatment, and support offer hope. Through continued efforts, we strive for improved outcomes and a brighter future. It is always advisable to seek medical help from an experienced neurologist. Timely care and help can ensure an appropriate diagnosis and treatment of your condition. 

At the CK Birla Hospital, we ensure patients get holistic medical support which includes treatment in a compassionate environment. This patient-centric approach not only helps patients heal better but also ensures they are aware of the preventive measures as well. In case you need to Consult a Neurologist, reach out to us, or book a direct appointment at the CK Birla Hospital.

FAQs

What is the Life Expectancy of Someone With SMA?

The life expectancy of someone with Spinal Muscular Atrophy (SMA) varies greatly depending on the type and severity of the condition, but it can range from infancy to adulthood.

Can Adults Develop SMA?

Yes, although it’s less common, adults can develop SMA due to genetic mutations or late-onset presentations. Symptoms may vary in severity and can appear later in life.

What are the Chances of Passing SMA to Offspring if One Parent is a Carrier?

If one parent is a carrier of the SMA gene mutation, each child has a 50% chance of inheriting the mutated gene, which could lead to SMA if both parents pass it on.

How Does SMA Affect Breathing and Respiratory Function?

SMA (Spinal Muscular Atrophy) weakens respiratory muscles, leading to difficulty breathing, reduced lung capacity, and increased susceptibility to respiratory infections, impacting overall respiratory function and potentially causing respiratory failure.