Synphilin-1 ((alpha)-synuclein interacting protein, SNCAIP) is a 919 amino acid protein that associates with (alpha) synuclein and promotes the formation of cytosolic inclusions in neuronal cells. The synuclein family members, including (alpha)-synuclein and (beta)-synuclein, are predominantly expressed in the brain, where they influence synaptic regulation and neuronal plasticity. Synphilin-1 contains modular protein domains, such as ankyrin-like repeats and a coiled-coil domain.While both (alpha)-synuclein and synphilin-1 are coexpressed in Lewy bodies of patients with Parkinson's disease, only mutations in the gene for (alpha)-synuclein have been determined to confer pathogenicity.