PRKN and Parkinson disease: PINK1 and Parkin knock-out (KO) mice display mild phenotypes with no dopaminergic neuron loss, a hallmark of PD, implying there are additional compensatory pathways contributing to neuronal mitophagy in vivo (Akundi et al., 2011; Goldberg et al., 2003; Kitada et al., 2007; Perez and Palmiter, 2005).