POLG and Leber hereditary optic neuropathy: Myoclonus may also be found in MELAS (Mitochondrial encephalopathy, lactate acidosis and stroke-like episodes), Leigh syndrome, Alpers syndrome, Leber hereditary optic neuropathy (LHON) or POLG (Polymerase Gamma) spectrum (ataxia, polyneuropathy, ophthalmoplegia), but often outside the context of a classical mitochondrial syndrome [65].