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Spinal Muscular Atrophy: Types, Causes, Symptoms, Hope for the Future

Spinal Muscular Atrophy: Types, Causes, Symptoms, Hope for the Future

Spinal Muscular Atrophy (SMA) is a group of rare genetic disorders that causes progressive degeneration of motor neurons in the spinal cord, muscle weakness and atrophy (wastage). The symptoms of SMA are usually evident from birth, and infants who exhibit hypotonia and breathing trouble should be tested immediately for a diagnosis. Research continues on why this rare condition presents and how it can be treated or even cured. In this blog, we’ll explore the condition in detail, covering its types, causes, symptoms, and management strategies, such as stem cell therapy for SMA. 

Understanding Spinal Muscular Atrophy

SMA occurs due to a loss in motor neurons responsible for controlling muscle movements in the body. The disorder primarily affects the muscles closer to the body’s center (proximal) rather than the muscles further away (distal). As these motor neurons degenerate, patients experience progressive muscle weakness and respiratory challenges. The symptoms and progression can vary in severity depending on the subtype of SMA. The early signs of SMA include:

  • Muscle weakness and loss of motor function: inability to achieve developmental motor milestones
  • Respiratory challenges: breathing difficulties owing to weakened respiratory muscles

Types of spinal muscular atrophy

There are five types of Spinal Muscular Atrophy:

Type 0 

This is the rarest and most severe subtype of spinal muscular atrophy. Patients move less while in the womb and frequently display joint defects and hypotonia at birth. Some may also have congenital heart defects. Respiratory failure is common owing to weak respiratory muscles, and most patients do not survive past their infancy.

Type I

This is also known as Werdnig-Hoffman disease and is the most common subtype of spinal muscular atrophy. Muscle weakness is present right from birth or a few months after, and children are generally unable to raise their heads or sit up unaided. Swallowing problems are a common symptom, which could lead to suboptimal feeding. Weakness in the respiratory muscles and an abnormal bell-shaped chest that prevents lungs from expanding fully also lead to breathing difficulties and respiratory failure. Most patients do not survive past early childhood.

Type II

Also known as Dubowitz disease, this type of spinal muscular atrophy affects children between 6-12 months of age. While they tend to need help with sitting up, they can stay seated without support. However, they cannot stand or walk without help, especially as they grow older and the muscle weakness worsens. Other symptoms include scoliosis, tremors in the fingers, and breathing problems. Most individuals live into their twenties or thirties.

Type III

Also known as Kugelberg-Welander disease, it typically sets in after early childhood. Patients may be able to stand and walk on their own initially, although this becomes progressively harder as the muscle weakness sets in. Life expectancy is usually normal, although patients may require a wheelchair later on.

Type IV

This is a rare subtype of spinal muscular atrophy that begins in early adulthood. Symptoms include mild to moderate muscle weakness and tremors as well as some breathing problems. Life expectancy tends to be normal.

Causes of spinal muscular atrophy

SMA occurs due to mutations in the SMN1 gene.

The subtype and severity of the condition depends on the number of copies of the SMN2 gene.

Both genes are responsible for controlling the production of the survival motor neuron (SMN) protein. The SMN protein is one among a group of proteins known as the SMN complex, which serve to maintain the motor neurons that transmit movement-related signals from the brain to the muscles.

In SMA, part of the SMN1 gene is missing, which inhibits SMN protein production and subsequently leads to motor neuron death. As a result, signals cannot be transmitted properly between the brain and the muscles. This causes muscles to weaken and waste away over time.

SMA is passed on in autosomal recessive fashion, with both copies of the SMN1 gene in each cell having the mutation.

Diagnosing SMA

In order to arrive at an SMA diagnosis, the following tests are generally recommended:

  • Genetic testing
  • Electromyography (EMG)
  • Muscle biopsy
  • Motor milestones assessment

Early detection and diagnosis are critical for timely intervention and positive outcomes..

SMA treatment options

Treatment for SMA generally involves a regenerative rehabilitation program that maximizes muscle control and ease of movement for the patient. The typical components of a treatment program are:

  • Physiotherapy: Imparts strength and flexibility to the muscles and thus aid gross and fine motor skills
  • Occupational Therapy: Helps patients complete daily activities like eating and dressing with as little assistance as possible
  • Speech Therapy: Helps patients articulate clearly and also gain more control over their swallowing and breathing
  • Stem Cell Therapy: A revolutionary type of treatment that uses the patient’s own cells to replace damaged nerve cells and thus potentially slow down disease progression
  • Surgery: Correction of certain bone or joint deformities

Stem cell therapy for SMA

Stem cell therapy is often considered in conjunction with other interventions for SMA, such as respiratory support, gene replacement therapy known as Zolgensma, and physical therapy.

In recent years, the use of mesenchymal stem cells (MSCs) to manage SMA has gained momentum. Owing to their anti-inflammatory and regenerative properties, MSCs can potentially stall (and eventually reverse) motor neuron degeneration and reduce inflammation.

Living with spinal muscular atrophy can be hard, which is why an early diagnosis and an intervention plan is critical. With proper treatment and mobility aids, patients can enjoy a much higher quality of life. In addition, parents and caregivers should surround their children with as much love and support as possible to help them navigate this condition with a smile. Additionally, there is continuous and relentless support for SMA research that is driving scientific understanding and medical technology to better treatments for the condition. We are slowly, but surely, moving to a world where SMA will no longer be a life-limiting condition.


Can spinal muscular atrophy be treated?

At present, a gene replacement therapy known as Zolgensma is the most widely recognised method for managing spinal muscular atrophy. The condition cannot be cured. It can only be managed.

Can you recover from spinal atrophy?

Spinal muscular atrophy does not go away. The symptoms can only be managed.

Can you live a normal life with spinal muscular atrophy?

Those with adult-onset SMA can continue to lead normal lives, while experiencing minor to major muscle weakness.

Who is at risk of spinal muscular atrophy?

Children of carriers of the faulty copy of SMN1 gene are at risk of spinal muscular atrophy.

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