POLG and sarcopenia: For example, D257A mutant of PolG directed reduced the content of electron transport chain (ETC) complexes I, III and IV which could promote skeletal muscle apoptosis and sarcopenia 35, and Tadafumi et.al constructed same model in PolG+/D257A mice which were recognized had no difference in phenotypes of WT mice 36, 37, while they found the motor dysfunction caused by heterozygous mutation PolG was significant milder than that in homozygous mutation mice 38.