Table 1.

Clinical syndromes associated with mitochondrial DNA mutations

Syndrome	Principal clinical features	Mitochondrial DNA mutation
CPEO	External ophthalmoplegia, myopathy	Single or multiple mtDNA deletions
Kearns-Sayre syndrome	Pigmentary retinopathy, ataxia, cardiac conduction defects	Single, large-scale mtDNA deletion
Leigh syndrome	Subacute necrotizing encephalopathy, basal ganglia lesions	Complex I, IV, and V gene mutations
LHON	Acute or sub-acute visual loss	Complex I gene mutations
MELAS	Myopathy, encephalopathy, lactic acidosis, stroke-like episodes	mt-tRNA gene mutations
MERRF	Myoclonus, epilepsy, ataxia	mt-tRNA gene mutations
NARP	Neuropathy, ataxia, pigmentary retinopathy	Complex V mutations
Pearson's marrow-pancreas syndrome	Sideroblastic anaemia, exocrine pancreatic insufficiency, hepatopathy, nephropathy	Single, large-scale mtDNA deletion

CPEO, chronic progressive external ophthalmoplegia; LHON, Leber's hereditary optic neuropathy; MELAS, myopathy, encephalopathy, and lactic acidosis with stroke-like episodes; MERRF, mitochondrial encephaolopathy with ragged red fibres; mtDNA, mitochondrial DNA; NARP, neurogenic ataxia and retinitis pigmentosa.