Table 2

Clinical syndromes associated with mitochondrial disease

SyndromePrimary featuresAdditional features
PEO, progressive external ophthalmoplegia.
Chronic progressive external ophthalmoplegia (CPEO)External ophthalmoplegia and bilateral ptosisMild proximal myopathy
Infantile myopathy and lactic acidosis (fatal and non-fatal forms)Hypotonia in the first year of life; feeding and respiratory difficultiesFatal form may be associated with a cardiomyopathy and/or the Toni-Fanconi-Debre syndrome
Kearns-Sayre syndrome (KSS)PEO onset before age 20 with pigmentary retinopathy, plus one of the following: CSF protein >1 g/l, cerebellar ataxia, heart blockBilateral deafness; myopathy; dysphagia; diabetes mellitus and hypoparathyroidism; dementia
Leber hereditary optic neuropathy (LHON)Subacute painless bilateral visual failure; male:female approx 4:1; median age of onset 24 yearsDystonia; cardiac pre-excitation syndromes
Leigh syndrome (LS)Subacute relapsing encephalopathy with cerebellar and brain stem signs presenting during infancyBasal ganglia lucencies
Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS)Stroke-like episodes before age 40 years; seizures and/or dementia; ragged-red fibres and/or lactic acidosisDiabetes mellitus; cardiomyopathy (hypertrophic leading to dilated); bilateral deafness; pigmentary retinopathy; cerebellar ataxia
Myoclonic epilepsy with ragged-red fibers (MERRF)Myoclonus; seizures; cerebellar ataxia; myopathyDementia, optic atrophy; bilateral deafness; peripheral neuropathy; spasticity; multiple lipomata
Neurogenic weakness with ataxia and retinitis pigmentosa (NARP)Late childhood or adult onset peripheral neuropathy with associated ataxia and pigmentary retinopathyBasal ganglia lucencies; abnormal electroretinogram; sensorimotor neuropathy
Pearson syndomeSideroblastic anaemia of childhood; pancytopenia; exocrine pancreatic failureRenal tubular defects