The synuclein family members, including (alpha)-synuclein (also designated NACP for non-(beta) amyloid component) and (beta)-synuclein, are predominantly expressed in the brain and are speculated to be involved in synaptic regulation and neuronal plasticity. (alpha)-synuclein is localized to neuronal cell bodies and synapses. (alpha)-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 (alpha)-synuclein was found to be upregulated, while (beta)-synuclein is downregulated, indicating that coordinate expression of synucleins may be important during hematopoetic cell differentiation. A mutant form of (alpha)-synuclein has been found in patients with early onset Parkinson's disease.