Atrophin-1 (AIP1) contains a polyglutamine repeat, expansion of which is responsible for dentatorubral and pallidoluysian atrophy. The protein encoded by this gene interacts with atrophin-1. This encoded protein is characterized by two WW domains, a guanylate kinase-like domain, and multiple PDZ domains. It has structural similarity to the membrane-associated guanylate kinase homologue (MAGUK) family. This protein is brain specific, where it appears to be widely expressed in both neurons and glia.