Major deletions or mutations in the mitochondrial genome of brain tissue have been associated with neurodegenerative diseases, and mtDNA point mutations have been linked to an insufficient energy supply in neurons.170–172 Further research revealed accumulated mtDNA mutations during aging in a mtDNA polymerase (POLG) mutant mouse model and worsened neurodegeneration in an AD mouse model established with mice bred with POLG mutant mice.173 Additionally, mutation accumulation is present in human neurodegenerative diseases. The gene discussed is POLG; the disease is Alzheimer disease.