SNCA and Parkinson disease: Thy1-aSyn mice exhibit a brain region-dependent 3- to 10-fold overexpression of human SNCA. 16Consequently, the effective dose of siSNCA used in this study can be expected to be more than adequate to silence SNCA in human tissue from patients with sporadic PD expressing endogenous levels of SNCA, and thus indicates a sufficiently broad therapeutic window.