POLG and Parkinson disease: However, POLG is a mitochondrial DNA polymerase, the dysfunction of which has a profound impact on the mitochondrial respiratory chain (Lax et al. 2016), and alterations to the mitochondrial respiratory chain have been consistently observed in PD and DLB (Hatton et al. 2020; Reeve et al. 2012; Schapira et al. 1990), which may point to some shared aetiological factors.