What is spinal muscular atrophy primarily caused by?

Spinal muscular atrophy (SMA) is primarily caused by the degeneration of motor neurons in the anterior horn of the spinal cord. These motor neurons are essential for muscle movement because they send signals from the spinal cord to the muscles. When these neurons degenerate, it leads to muscle weakness and atrophy, affecting voluntary movements. This degeneration is typically due to a genetic defect in the SMN1 gene, which is crucial for the maintenance and survival of motor neurons. In contrast, options like infection, trauma, or malnutrition may contribute to neurological issues but are not the underlying cause of SMA. The condition's hallmark is specifically tied to the loss of motor neurons, making it a neurodegenerative disorder rather than one resulting from external factors or systemic conditions.