Table I.

Mitochondrial myopathy syndromes presenting with ocular myopathy.

Syndrome	Clinical symptoms/signs	Onset age	Genetics
Progressive external ophthalmoplegia (PEO)	Ptosis, ophthalmoplegia. Proximal myopathy often present. Various other clinical features variably present	Any age of onset. Typically more severe phenotype with younger onset	mtDNA single deletions; mtDNA point mutations (including m.3243A >G, m.8344A >G); nDNA mutations (POLG, ANT, PEO1, OPA1)
Kearns–Sayre syndrome (KSS)	PEO, ptosis, pigmentary retinopathy, cardiac conduction abnormality, ataxia, CSF elevated protein, diabetes mellitus, sensorineural hearing loss, myopathy	<20 years	mtDNA single deletions
Ataxia neuropathy syndromes (ANS): Including MIRAS, SCAE, SANDO, MEMSA	SANDO: PEO, dysarthria, sensory neuropathy, cerebellar ataxia. Other ANS: variable presence of PEO and/or myopathy	Teen or adult	nDNA mutations (POLG, PEO1)
Myopathy, neurogastrointestinal encephalopathy (MNGIE)	PEO, ptosis, GI dysmotility, proximal myopathy, axonal polyneuropathy, leukodystrophy.	Childhood to early adulthood	nDNA mutations in TYMP

MEMSA = myoclonic epilepsy myopathy sensory ataxia; MIRAS = mitochondrial recessive ataxia syndrome; SANDO = sensory ataxia neuropathy dysarthria ophthalmoplegia; SCAE = spinocerebellar ataxia with epilepsy.