SNCA and Parkinson disease: Upon axonal injection, the protein is diluted 10–20x for a final concentration of 7–16 μM, which is 2–3 times the estimated endogenous levels of α-synuclein at mammalian synapses (Westphal and Chandra, 2013) and consistent with overexpression levels observed in PD brains (Singleton et al., 2003).