SMA (Spinal Muscular Atrophy) is a progressive, genetically inherited muscle disease that causes the loss of motor nerve cells in the spinal cord. These motor neurons control muscle movement. In SMA, the function of these cells is impaired, they gradually degenerate, and this leads to muscle weakness and muscle wasting (atrophy).
Genetic Basis
SMA is a genetic disorder inherited in an autosomal recessive manner. This means that for the disease to occur, a child must inherit a defective SMN1 (Survival Motor Neuron 1) gene from both the mother and the father.
- The SMN1 gene produces a protein essential for the healthy functioning of motor neurons.
- If this gene does not function properly, motor neurons cannot receive enough of this protein and gradually die.
Types of SMA
SMA is classified into several types based on the age of onset and disease progression:
- Type 1 (Werdnig-Hoffmann Disease):
The most severe and most common form. It begins in infancy. Babies have difficulty holding their head up, sucking, and swallowing. Without treatment, life expectancy is significantly reduced. - Type 2:
Begins between 6 and 18 months of age. Children can sit independently but cannot walk. - Type 3 (Kugelberg-Welander Disease):
Usually begins in childhood or adolescence. Individuals can walk, but muscle weakness increases over time. - Type 4:
Begins in adulthood and is the mildest form.
Diagnostic Methods
SMA is typically diagnosed using the following methods:
- Genetic testing: Detection of mutations in the SMN1 gene
- EMG (Electromyography): Measures the electrical activity of muscles and nerves
- Muscle biopsy: Rarely used; examines structural changes in muscle tissue
Treatment and Support
In the past, SMA had no treatment, but in recent years, innovative gene therapies and medications have brought promising advancements:
- Spinraza (Nusinersen):
Administered via lumbar injection. It increases SMN protein production by supporting the SMN2 gene. - Zolgensma:
A one-time gene therapy that aims to replace the faulty SMN1 gene. Early administration is crucial. - Evrysdi (Risdiplam):
An oral medication that increases SMN protein production from the SMN2 gene.
In addition, multidisciplinary approaches such as physiotherapy, respiratory support, and nutritional monitoring play a vital role in the treatment process.
Conclusion
SMA is a serious neuromuscular disease that can be managed with early diagnosis and appropriate treatment but requires lifelong follow-up. Genetic counseling and carrier screening are also extremely important for raising awareness among at-risk families and for preventing the disease.
