The progressive, late-onset neurodegenerative diseases (PEO, Parkinsonism, etc.)are often caused by mutations in the active site of Pol-γA (Stumpf and Copeland, 2011), which can lead to reductions in kcat/Km, kcat, and fidelity of replication (Batabyal et al., 2010; Estep and Johnson, 2011; Ziehr et al., unpublished). Here, POLG is linked to Parkinson disease.