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The rare mitochondrial DNA (mtDNA) variant m.8340G>A has been previously reported in the literature in a single, sporadic case of mitochondrial myopathy. In this report, we aim to investigate the case of a 39-year-old male patient with sensorineural deafness who presented to the eye clinic with nyctalopia, retinal pigmentary changes and bilateral cortical cataracts.The patient was examined clinically and investigated with autofluorescence, full-field electroretinography, electro-oculogram and dark adaptometry. Sequencing of the mitochondrial genome in blood and muscle tissue was followed by histochemical and biochemical analyses together with single fibre studies of a muscle biopsy to confirm a mitochondrial aetiology.Electrophysiology, colour testing and dark adaptometry showed significant photoreceptor dysfunction with macular involvement. Sequencing the complete mitochondrial genome revealed a rare mitochondrial tRNALys (MTTK) gene variant-m.8340G>A-which was heteroplasmic in blood (11%) and skeletal muscle (65%) and cosegregated with cytochrome c oxidase-deficient fibres in single-fibre studies.We confirm the pathogenicity of the rare mitochondrial m.8340G>A variant the basis of single-fibre segregation studies and its association with an expanded clinical phenotype. Our case expands the phenotypic spectrum of diseases associated with mitochondrial tRNA point mutations, highlighting the importance of considering a mitochondrial diagnosis in similar cases presenting to the eye clinic and the importance of further genetic testing if standard mutational analysis does not yield a result.

Original publication

DOI

10.1136/bjophthalmol-2017-310370

Type

Journal article

Journal

The British journal of ophthalmology

Publication Date

09/2017

Volume

101

Pages

1298 - 1302

Addresses

John Radcliffe Hospital, Oxford, UK.

Keywords

Muscle, Skeletal, Mitochondria, Muscle, Humans, Electron Transport Complex IV, Succinate Dehydrogenase, Thymidine Kinase, DNA, Mitochondrial, RNA, Transfer, Lys, Electroretinography, Electrooculography, DNA Mutational Analysis, Point Mutation, Adult, Male, Usher Syndromes, Photoreceptor Cells, Vertebrate, Optical Imaging