POLG and autosomal recessive progressive external ophthalmoplegia: The six leading disorders caused by POLG mutations are Alpers-Huttenlocher syndrome, childhood myocerebrohepatopathy spectrum, myoclonic epilepsy myopathy sensory ataxia, ataxia neuropathy spectrum, autosome recessive progressive external ophthalmoplegia, and autosome dominant progressive external ophthalmoplegia.