PRKN and Parkinson disease: Although several groups have demonstrated that PD-associated parkin mutants are defective in supporting mitophagy due to distinct problems at recognition, transportation, or ubiquitination of impaired mitochondria (Lee et al., 2010; Matsuda et al., 2010), a pertinent question to ask is whether deficient mitochondrial QC is relevant at all to the large number sporadic PD cases where parkin is not mutated.