AOX1 (Aldehyde oxidase 1) is a 1338 amino acid cytoplasmic protein that catalyzes the oxidation of a variety of aldehydes, leading to the production of hydrogen peroxide. Under certain conditions, AOX1 can catalyze the formation of the superoxide free radical. Defects in oxygen radical metabolism have been linked to the pathogenesis of amyotrophic lateral sclerosis (ALS), an autosomal dominant neurodegenerative disorder characterized by the death of motor neurons in the spinal cord, brain and brainstem. Significantly, AOX1 is highly expressed in the ventral horn of the spinal cord and the gene that encodes AOX1 is located in a chromosomal region that is frequently found to be implicated in ALS2. This evidence suggests that AOX1 is a candidate gene for ALS2.