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. Here, POLG is linked to inborn mitochondrial metabolism disorder.