Although several distinct phenotypes have been reported in association with POLG mutations including childhood-onset Alpers-Huttenlocher syndrome, autosomal recessive and dominant of forms of PEO, myoclonic epilepsy, myopathy and sensory ataxia (MEMSA) and the ataxia-neuropathy spectrum (ANS) disorders, current thinking suggests that these previously defined syndromes are not discrete clinical entities but rather overlap considerably and lie on a continuum. This evidence concerns the gene POLG and cerebellar ataxia.