Clinical syndrome

Primary features

Additional features

Chronic progressive external ophthalmoplegia (CPEO)

External ophthalmoplegia and bilateral ptosis

Mild proximal myopathy

Infantile myopathy and lactic acidosis (fatal and non‐fatal forms)

Hypotonia in the first year of life Feeding and respiratory difficulties

Fatal 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 greater than 1 g/l, cerebellar ataxia, heart block

Bilateral deafness
Myopathy
Dysphagia
Diabetes mellitus and hypoparathyroidism
Dementia

Leber hereditary optic neuropathy(LHON)

Subacute painless bilateral visual failure
Males: females approx. 4:1 Median age of onset 24 years

Dystonia
Cardiac pre‐excitation syndromes

Leigh syndrome (LS)

Subacute relapsing encephalopathy with cerebellar and brain‐stem signs presenting during infancy

Basal 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 acidosis

Diabetes mellitus
Cardiomyopathy (hypertrophic leading to dilated)
Bilateral deafness
Pigmentary retinopathy
Cerebellar ataxia

Myoclonic epilepsy with ragged‐red fibers (MERRF)

Myoclonus
Seizures
Cerebellar ataxia
Myopathy

Dementia, 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 retinopathy

Basal ganglia lucencies
Abnormal electroretinogram
Sensori‐motor neuropathy

Pearson Syndome

Sideroblastic anemia of childhood
Pancytopenia
Exocrine pancreatic failure

Renal tubular defects