What neurological disorder is associated with muscle weakness and atrophy in children?

Spinal muscular atrophy (SMA) is a genetic disorder primarily affecting motor neurons in the spinal cord, leading to muscle weakness and atrophy, especially in children. It is caused by a defect in the survival motor neuron (SMN) gene, which results in the progressive degeneration of motor neurons. As the motor neurons die, the connections between the nervous system and the muscles weaken, resulting in a decrease in muscle strength and size. Children with SMA often present with symptoms such as difficulty in movement, weakness in the arms and legs, and challenges with breathing and swallowing as the condition progresses.

The other disorders listed, while also involving muscle function and neurological components, have different underlying mechanisms or age of onset. Multiple sclerosis typically manifests in young adulthood rather than childhood and involves an immune-mediated process affecting the central nervous system. Muscular dystrophy is characterized by muscle degeneration due to genetic mutations but differs in its progression and presentation. Myasthenia gravis is an autoimmune disorder that leads to muscle weakness due to impaired neural transmission but is generally not categorized as a primary disorder affecting children as SMA is. Therefore, the defining characteristics of SMA make it the correct association with muscle weakness and atrophy specifically in children.