The synuclein family members, including ?-synuclein (also designated NACP for non-? amyloid component) and ?-synuclein, are predominantly expressed in the brain and are speculated to be involved in synaptic regulation and neuronal plasticity. ?-synuclein is localized to neuronal cell bodies and synapses. ?-synuclein was first identified as a component of Alzheimer’s disease amyloid plaques. Abnormal platelet function in Alzheimer’s disease has been demonstrated. During megakaryocytic differentiation ?-synuclein was found to be up-regulated, while ?-synuclein is down-regulated, indicating that coordinate expression of synucleins may be important during hematopoetic cell differentiation. A mutant form of ?-synuclein has been found in patients with early onset Parkinson’s disease.