GBA1 and Parkinson disease: To test the hypothesis that the gene mutations can be related to α-syn spread, α-syn preformed fibrils were injected into the olfactory bulb of mice carrying GBA D409V+/- and ATP13a2; these mutations did not exacerbate behavioral impairments or histopathology (α-syn, LAMP2, and Iba1) when compared to their wild-type littermates [187], reinforcing the unclear role that GBA has in PD development.