Sporadic Amyotrophic Lateral Sclerosis Due to a FUS P525L Mutation with Asymmetric Muscle Weakness and Anti-ganglioside Antibodies.

Amyotrophic lateral sclerosis (ALS) due to a fused in sarcoma (FUS) P525L mutation is characterized by a rapidly progressive course. Multifocal motor neuropathy (MMN) may resemble ALS in early stage and is associated with anti-ganglioside antibodies. A 38-year-old woman was admitted to our hospital because of progressive muscle weakness in the right limbs. She had mild mental retardation and minor deformities. Initially, we suspected MMN given the asymmetric muscle weakness and detection of anti-ganglioside antibodies. However, physical and electrophysiological tests did not support MMN, instead suggesting ALS. We confirmed a heterozygous P525L mutation and finally diagnosed this case as ALS due to an FUS mutation.