PRKN and Parkinson disease: Our findings may help to address an important puzzle in the field of PD research: why do PINK1 or parkin knockout mice, or even parkin/DJ-1/PINK1 triple knockout mice, bear only subtle phenotypes related to dopaminergic neuronal degeneration or mitochondrial morphology changes (Palacino et al., 2004; Perez and Palmiter, 2005; Perez et al., 2005; Kitada et al., 2007; Frank-Cannon et al., 2008; Gautier et al., 2008; Gispert et al., 2009; Kitada et al., 2009; Akundi et al., 2011).