POLG and Parkinson disease: Indeed, prominent loss of TH-positive SN neurons was determined in the two POLG cases with severe combined OxPhos deficiency (POLG02 and POLG03) and in 8/9 PD cases12 (Supplementary Fig. 4), with the exception of PD08 in which normal OxPhos protein expression was detected (Fig. 6a–j).