Primary lateral sclerosis

Primary lateral sclerosis is a very rare neuromuscular disease characterized by progressive muscle weakness in the voluntary muscles. It belongs to the motor neuron disease category, in which nerve cells controlling voluntary movement degenerate and die; unlike amyotrophic lateral sclerosis, it affects only upper motor neurons without evidence of spinal motor neuron degeneration or muscle wasting. Its exact cause remains unclear, though researchers suspect a combination of environmental and genetic factors; a rare juvenile form may involve the ALS2 gene, while adult-onset primary lateral sclerosis is not considered hereditary.