DAO and psychotic disorder: In addition to its role in psychosis and cognition, DAO may be involved in amyotrophic lateral sclerosis, a neuronal disease involving the progressive loss of motoneurons; specifically, a single nucleotide polymorphism that yielded the dysfunctional point mutation R199→W was found in the gene encoding DAO in the genomes of a family with the disease [8], resulting in an accumulation of d-serine, excitotoxicity, and motoneuron death.