PRKN and Parkinson disease: Similar to other PD genetic mouse models, such as α-synuclein transgenic [12-14], parkin-/- [15,16], DJ-1-/- [17,18], PINK1-/- [19,20], and LRRK2 transgenic and knockin mice [21-25], LRRK2-/- brains did not develop overt dopaminergic degeneration [26].