Interestingly, after crossing the Mutator mouse, which possesses a proofreading-deficient form of POLG, the polymerase responsible for mtDNA replication, resulting in accumulation of mtDNA deletions, with a PRKN knock-out mouse, which both by themselves do not show neurodegeneration, the resulting double knockout displays obvious mitochondrial dysfunction and PD pathology. The gene discussed is PRKN; the disease is Parkinson disease.