MT-CO3 and Leber hereditary optic neuropathy: Our initial analyses of known regulators of mtDNA copy number with COXIII (Figure 4) revealed no obvious mechanism for COXIII to directly modify mtDNA copy number; however, Pello et al [71] reported that m.9667A>G causes respiratory chain assembly deficiencies in patients with Leber's hereditary optic neuropathy.