Spinal Muscular Atrophy: An Overview

Spinal Muscular Atrophy is a rare genetic disorder that causes progressive muscle weakness and wastage. The symptoms 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. Here, we provide a brief guide to what we know so far.

Understanding Spinal Muscular Atrophy

Spinal Muscular Atrophy is a genetic disorder that causes weakness and wastage (atrophy) in the skeletal muscles. It occurs due to a loss in motor neurons and primarily affects the muscles closer to the body’s center (proximal) rather than the muscles further away (distal). Patients experience progressive muscle weakness and breathing problems, also these can vary in severity depending on the subtype of Spinal Muscular Atrophy. Treatment can help to manage the symptoms and improve quality of life. Spinal Muscular Atrophy affects about one in every 8000–10000 people worldwide.

Types of Spinal Muscular Atrophy

There are five main 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

Spinal Muscular Atrophy 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 of these 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 Spinal Muscular Atrophy, 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.

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

Treatment for Spinal Muscular Atrophy

Treatment for Spinal Muscular Atrophy 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, to impart strength and flexibility to the muscles and thus aid gross and fine motor skills

Occupational Therapy, to help patients complete daily activities like eating and dressing with as little assistance as possible

Speech Therapy, to help 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 progress

Surgery, to correct certain bone or joint deformities

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.

A highly regarded neurologist and stem cell specialist, Dr Na’eem Sadiq studied neurology and clinical neurophysiology in London before working with some of England’s and the Middle East’s most prestigious medical institutions. He completed his MBBS