The synucleins, including (alpha)-synuclein (also designated NACP for nonamyloid component precursor), (beta)-synuclein (also designated PNP 14 for phosphoneuroprotein 14), and (gamma)-synuclein (also designated persyn or BCSG1 for breast cancer-specific gene 1) are presynaptic proteins abundant in neurons. (alpha)-Synuclein, identified as a component of Alzheimer's disease amyloid plaques, is localized to neuronal cell bodies and synapses. Coordinate expression of (alpha)-synuclein and (beta)-synuclein may be important during hematopoetic cell differentiation. A mutant form of (alpha)-synuclein is found in patients with early onset Parkinson's disease. (gamma)-Synuclein is associated with axonal pathology in Parkinson's disease.