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Spinal muscular atrophy (SMA) is a neuromuscular disorder that is inherited and causes muscles to weaken and waste away. SMA patients have a specific type of nerve cell (called motor neurons) in the spinal cord that controls muscle movement. Muscles do not receive nerve signals that cause them to move unless these motor neurons are present. Atrophy is a medical term that implies "smaller." Due to a lack of use, specific muscles in SMA shrink and weaken.
SMA affects between 10,000 and 25,000 children and adults in the United States. It is an uncommon condition that affects around one out of every 6,000 to 10,000 children.
WHO IS AT RISK OF DEVELOPING SPINAL MUSCULAR ATROPHY?
A person with SMA inherits two copies of the survival motor neuron 1 (SMN1) gene, which is either absent or defective (mutated). One defective gene is inherited from the mother, while the other is inherited from the father. An adult can have a single copy of the faulty gene that causes SMA and be unaware of it.
The mutant SMN1 gene affects around six million Americans (1 in 50). These carriers have one healthy SMN1 gene and one that is absent or faulty. Carriers do not create SMA. Two carriers have a one-in-four probability of having a kid with SMA.
WHAT ARE THE TYPES OF SPINAL MUSCULAR ATROPHY?
SMA is classified into four types:
- Type 1 (severe): Type 1 SMA, commonly known as Werdnig-Hoffman disease, affects around 60% of patients with SMA. Symptoms arise shortly after birth or within the first six months of an infant's life. Type 1 SMA infants have difficulty eating and sucking. They do not reach regular developmental milestones such as holding their heads up or sitting. As children's muscles deteriorate, they become more vulnerable to respiratory infections and lung collapse (pneumothorax). The majority of children with type 1 SMA die before reaching the age of two.
- Type 2 (intermediate): Type 2 SMA (also known as Dubowitz disease) symptoms emerge between the ages of six and 18 months. This variety usually affects the lower limbs. Children with type 2 SMA can sit up but cannot walk. The majority of children with type 2 SMA survive into adulthood.
- Type 3 (mild): Type 3 SMA (also known as Kugelbert-Welander or juvenile-onset SMA) symptoms occur after a child's first 18 months of life. Some patients with type 3 diabetes do not show symptoms until they are in their early twenties. Mild muscle weakness, difficulties walking, and frequent respiratory infections are also signs of type 3. Symptoms can impair one's ability to walk or stand over time. Type 3 SMA has no substantial impact on life expectancy.
- Type 4 (adult): The adult type of SMA is uncommon and usually appears in the mid-30s. Because muscle weakening signs develop slowly, most persons with type 4 remain mobile and lead full lives.
WHAT ARE THE CAUSES OF SPINAL MUSCULAR ATROPHY?
People with SMA either lack a portion of the SMN1 gene or have a faulty (mutated) gene. SMN protein is produced by a healthy SMN1 gene. This protein is required for motor neurons to survive and function properly.
Because people with SMA do not produce enough SMN protein, their motor neurons atrophy and die. As a result, the brain is unable to govern voluntary motions, particularly those involving the head, neck, arms, and legs.
People also have SMN2 genes, which create a trace of SMN protein. An SMN2 gene can be found in up to eight different people. Because the extra genes compensate for the missing SMN1 protein, having several copies of the SMN2 gene usually results in less severe SMA symptoms. Non-SMN gene mutations (non-chromosome 5) cause SMA in rare cases.
WHAT ARE THE SYMPTOMS OF SPINAL MUSCULAR ATROPHY?
People also have SMN2 genes, which create a trace of SMN protein. An SMN2 gene can be found in up to eight different people. Because the extra genes compensate for the missing SMN1 protein, having several copies of the SMN2 gene usually results in less severe SMA symptoms. Non-SMN gene mutations (non-chromosome 5) cause SMA in rare cases.
WHAT ARE THE COMPLICATIONS OF SPINAL MUSCULAR ATROPHY?
People with SMA have gradual muscle weakness and loss of muscle control over time. Among the possible complications are:
- Scoliosis, hip dislocation, and bone fractures (curvature of the spine).
- Malnutrition and dehydration as a result of eating and swallowing difficulties that may need the use of a feeding tube.
- Pneumonia and respiratory illnesses
- Weak lungs and respiratory issues that may necessitate breathing assistance (ventilation).
HOW IS SPINAL MUSCLAR ATROPHY DIAGNOSED?
Some SMA symptoms are similar to those seen in neuromuscular illnesses such as muscular dystrophy. Your healthcare professional will perform a physical exam and take a medical history to determine the origin of your symptoms. To diagnose SMA, your doctor may additionally perform one or more of the following tests:
- Blood test: Creatine kinase levels can be checked using an enzyme and protein blood test. This enzyme is released into the bloodstream by deteriorating muscles.
- Genetic test: This blood test detects issues with the SMN1 gene. A genetic test is 95% efficient as a diagnostic technique for identifying the mutated SMN1 gene. SMA is tested for in several jurisdictions as part of regular newborn screenings.
- Nerve conduction test: The electrical activity of nerves, muscles, and nerves is measured by an electromyogram (EMG).
- Muscle biopsy: A physician may occasionally do a muscle biopsy. A little sample of muscle tissue is removed and sent to a lab for analysis during this treatment. A biopsy may reveal atrophy, or muscle loss.
IS IT POSSIBLE TO DIAGNOSE SPINAL MUSCULAR ATROPHY DURING PREGNANCY?
Prenatal diagnostics can detect if your unborn child has SMA if you are pregnant and have a family history of the condition. These tests raise the chance of miscarriage or pregnancy loss somewhat. SMA prenatal testing include:
- Amniocentesis: Your obstetrician will place a thin needle into your tummy to extract a small amount of fluid from the amniotic sac during amniocentesis. A pathologist (lab specialist) examines the fluid for SMA. This test is administered after the 14th week of pregnancy.
- CVS (chorionic villus sampling): A tiny tissue sample from the placenta is removed by your obstetrician through the mother's cervix or stomach. SMA is detected in the material by a pathologist. CVS can occur as early as the tenth week of pregnancy.
HOW CAN SPINAL MUSCULAR ATROPHY BE TREATED?
SMA does not have a cure. Treatment options are determined by the type of SMA and the symptoms. Physical and occupational therapy, as well as assistive devices such as orthopaedic braces, crutches, walkers, and wheelchairs, benefit many persons with SMA.
These therapies may also be beneficial:
Disease-modifying treatment: These medications increase the production of the SMN protein. Nusinersen (Spinraza®) is recommended for children aged 2 to 12. The medicine is injected into the area around the spinal canal by your provider. Risdaplam (Evrysdi®), a separate medicine, benefits adults and children over the age of two months. Risdaplam is taken orally every day (orally).
Gene replacement therapy: A one-time intravenous (IV) infusion of onasemnogene abeparvovec-xioi (Zolgensma®) may benefit children under the age of two. This therapy replaces a damaged or missing SMN1 gene with a functional gene.
HOW CAN SPINAL MUSCULAR ATROPHY PREVENTED?
SMA is a hereditary condition. A genetic counselor can discuss the possibilities of your child developing SMA or being a carrier if you or your spouse possesses the faulty gene that causes SMA.
You may be able to reduce your risk of passing on SMA before becoming pregnant. Preimplantation genetic diagnosis (PGD) is a procedure that identifies embryos that do not carry the defective gene. During in vitro fertilization, your doctor implants healthy embryos (IVF). PGD guarantees that your child will have two healthy SMN1 genes and will not have SMA.
CONCLUSION
SMA is a hereditary neuromuscular disorder that can have a negative impact on both quality of life and life expectancy. It is a chronic condition that worsens over time. Symptoms can appear at birth (type 1), develop during childhood (types 2 or 3), or appear later in life (type 4). (type 4). Newer gene replacement and disease-modifying medicines show promise. It is possible to carry the SMA gene and be unaware of it. If SMA runs in your family, talk to your doctor about measures to reduce your future baby's risk.