POLG and mitochondrial disease: It must be considered that approximately 1% of the population is carrier of a POLG mutation, indicating that the potential frequency of POLG-related disorders is about 1/10,000; in fact, it has been estimated that 10% of adult mitochondrial diseases and 10–25% of PEO are caused by mutations in POLG, and that the present underestimation of the reported cases will be corrected due to amelioration and precocity of the diagnosis1.