POLG mutations can, therefore, lead to a spectrum of mitochondrial diseases with dominant or recessive type of inheritance, which can be divided into three main groups: sporadic/familial progressive external ophthalmoplegia (PEO) (OMIM #157640 and #258450), adult-onset ataxia (OMIM #607459), and Alpers syndrome (OMIM #203700). This evidence concerns the gene POLG and mitochondrial disease.