Approximately 1 in every 7,000 newborns around the world suffer from Spinal Muscular Atrophy (SMA), which is considered one of the most deadly genetic diseases in infancy. SMA is a severe and unusual condition that acts progressively, causing a gradual decline in the quality of life of the affected child or adult.
In the following post, you will learn about the origin, symptoms, and different types of spinal muscular atrophy. This information can help you detect the onset of the disease, especially when children are involved, as the muscular degeneration is more severe and common in this population.
Spinal Muscular Atrophy: What is it and how to detect it?
Spinal Muscular Atrophy (SMA) is a group of genetic and hereditary neuromuscular diseases that directly affect motor neurons. Motor neurons are responsible for controlling the proper functioning of arms, legs, chest, face, throat, and tongue.
As nerve cells die off, muscle weakness and atrophy begin; over time, SMA can limit speech, swallowing, breathing, and walking.
The diagnosis of spinal muscular atrophy must be confirmed by a physician, who, in addition to performing a physical examination and patient history, will evaluate family history and conduct various genetic tests (blood tests, electromyography, nerve conduction, or muscle biopsy) to validate the diagnosis.
What causes spinal muscular atrophy?
The main cause of SMA is changes in the SMN1 gene; this gene is responsible for producing a protein that contributes to the development and growth of healthy motor neurons. When there is a deficiency of this protein, nerve cells undergo premature deterioration, leading to their death.
Babies inherit 2 copies of the SMN1 gene in their DNA, one from the father and one from the mother. Spinal muscular atrophy develops when both copies of the gene have the same genetic alteration. Generally, changes in the SMN1 gene are passed from parents to children.
Symptoms of spinal muscular atrophy
Muscle weakness is the hallmark symptom of spinal muscular atrophy, which progressively worsens over time. In most cases, muscle weakness begins in the shoulder and leg muscles, and the condition worsens over time, becoming severe when it affects the respiratory muscles.
In children with SMA, it can lead to postural changes, recurrent respiratory infections, and a nasal voice. During the physical examination of an infant with spinal muscular atrophy, the doctor may notice weak muscles, lack of tendon reflexes, and spasms in the tongue muscles.
Types of spinal muscular atrophy
There are several types of this neurodegenerative disease, each presenting different characteristics and symptoms based on the age at which the disease begins. Below, we will expand on the information about each type.
Spinal Muscular Atrophy Type 1
Also known as Werdnig-Hoffmann disease or infantile-onset spinal muscular atrophy, this is the most aggressive and common type. SMA type 1 manifests before 6 months of age, causing severe muscle weakness. Infants with this condition are born with very low muscle tone, which prevents them from holding up their heads or moving spontaneously; additionally, they have difficulties with eating and breathing.
Life expectancy in Spinal Muscular Atrophy Type 1
Without proper treatment and supportive care, the disease can have a significant impact on the child’s quality of life and life expectancy. The life expectancy of babies with SMA type 1 is approximately 2 to 3 years.
Spinal Muscular Atrophy Type 2
SMA type 2 or Dubowitz disease starts after 6 months of age and can be delayed until 12 or 18 months of age. Although infants with this condition show weak muscles from birth, during the first months, they may be able to sit up on their own. After this, the atrophy tends to progress and limit the child’s development.
Children with type 2 SMA show evident signs such as involuntary finger movements, muscle flaccidity, scoliosis, and weakened respiratory muscles.
Life expectancy in Spinal Muscular Atrophy Type 2
Patients with SMA type 2 can have a life expectancy into adulthood if they receive proper care and treatment. However, without treatment, life expectancy may be limited to adolescence.
Spinal Muscular Atrophy Type 3
Spinal Muscular Atrophy Type 3 or Kugelberg-Welander disease is the mildest in children. Symptoms of the disease appear after 18 months of age, with the lower extremities being most affected. Typically, children can walk independently, but they are more susceptible to frequent falls.
Life expectancy in Spinal Muscular Atrophy Type 3
The later the onset of the neurodegenerative disease, the more favorable the prognosis. Children with SMA type 3 can live into early adulthood and even lead a normal life.
Spinal Muscular Atrophy Type 4
Also known as adult-onset spinal muscular atrophy, this disease develops around the age of 30. Symptoms start mildly and gradually become moderate, but they do not become severe or life-threatening. Adults with SMA type 4 experience tremors, spasms, and muscle weakness.
Life expectancy in Spinal Muscular Atrophy Type 4
In adults, the disease progresses more slowly compared to other types of childhood SMA. Spinal Muscular Atrophy Type 4 is not fatal, so the affected person will have a normal life expectancy.
Treatment for Spinal Muscular Atrophy
SMA is a disease that has no cure; therefore, treatment primarily focuses on managing symptoms and preventing any associated complications.
Conservative treatments for spinal muscular atrophy include:
Medications to promote the production of essential proteins for motor neurons.
Gene therapy (in children with SMA under 2 years of age).
Physical therapy and rehabilitation to delay muscular atrophy, improve joint movement, and promote blood flow.
Assistive mobility devices (crutches, canes, wheelchairs, orthopedic appliances, etc.).
Nutritional support to ensure proper nutrition during the disease.
Respiratory physiotherapy or respiratory support for patients with muscle weakness in the neck, throat, and chest.
Can spinal muscular atrophy be detected during pregnancy?
Spinal Muscular Atrophy Type 0 in a prenatal form is the most deadly of all. The mother may notice a decrease in fetal movements during the last trimester of pregnancy.
Parents with a family history of the disease or with suspicions of it can undergo prenatal testing through amniocentesis specifically for the SMN1 gene (associated with spinal muscular atrophy). Unfortunately, babies diagnosed with this condition usually pass away before their first 6 months of life.
Can spinal muscular atrophy be prevented?
Spinal muscular atrophy is neither curable nor preventable. Early detection of the disease is essential to improve the patient’s quality of life by addressing respiratory and nutritional issues in children with atrophy, making the disease as less traumatic as possible.
