Spinal Muscular Atrophy (SMA) is a genetic disorder characterized by weakness and wasting (atrophy) in muscles used for movement (skeletal muscles). It results from the loss of motor neurons in the spinal cord and brainstem. SMA primarily affects infants and children, and its severity can vary widely among individuals.
Symptoms of SMA
The symptoms of SMA depend on the type and severity of the condition:
- Type 1 (Severe) – Werdnig-Hoffmann Disease:
- Onset: Birth to 6 months
- Symptoms: Severe muscle weakness, poor muscle tone, difficulty breathing and swallowing, limited movement, and lack of developmental milestones (such as sitting and crawling).
- Type 2 (Intermediate) – Dubowitz Disease:
- Onset: 6 to 18 months
- Symptoms: Moderate muscle weakness, inability to stand or walk without assistance, respiratory problems, tremors in the fingers, and scoliosis.
- Type 3 (Mild) – Kugelberg-Welander Disease:
- Onset: After 18 months to early adulthood
- Symptoms: Mild to moderate muscle weakness, difficulty walking or running, and potential for wheelchair use in adulthood.
- Type 4 (Adult-Onset):
- Onset: Adulthood (after age 21)
- Symptoms: Mild to moderate muscle weakness, especially in the proximal muscles (closer to the body’s core), and slower progression of symptoms.
Causes of SMA
SMA is caused by mutations in the SMN1 (Survival Motor Neuron 1) gene. This gene produces a protein essential for the survival of motor neurons. Without enough of this protein, motor neurons deteriorate and die, leading to muscle weakness and atrophy.
SMA is inherited in an autosomal recessive manner, meaning that an individual must inherit two copies of the faulty gene (one from each parent) to develop the disorder.
Treatment of SMA
While there is no cure for SMA, several treatments can help manage the symptoms and improve quality of life:
- Medications:
- Nusinersen (Spinraza): An antisense oligonucleotide that increases the production of the SMN protein.
- Onasemnogene abeparvovec (Zolgensma): A gene therapy that introduces a functional copy of the SMN1 gene into motor neurons.
- Risdiplam (Evrysdi): A small molecule that increases SMN protein levels by modifying the SMN2 gene splicing.
- Supportive Care:
- Physical Therapy: To maintain muscle strength and flexibility.
- Occupational Therapy: To assist with daily activities and enhance quality of life.
- Respiratory Therapy: To manage breathing difficulties and prevent respiratory infections.
- Nutritional Support: To ensure adequate nutrition and manage swallowing difficulties.
- Orthopedic Care:
- Bracing and Surgery: To manage scoliosis and joint deformities.
Prevention of SMA
Currently, there is no way to prevent SMA in individuals already carrying the genetic mutation. However, genetic counseling and carrier screening can help prospective parents understand their risk of having a child with SMA. Prenatal and preimplantation genetic diagnosis can also identify the condition early in pregnancies at risk.
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