PRKN and Parkinson disease: Although dopaminergic neuronal loss is not observed in either PINK1 or Parkin KO mice, we recently found that when Parkin is deleted in mice that express a proof-reading-defective version of the mtDNA polymerase (POLG), the so-called Mutator mouse, certain features of PD pathogenesis develop, including dopaminergic neuron degeneration and motor defects [79].