University of Oulu

Kärppä, M., Kytövuori, L., Saari, M., Majamaa, K. (2018) Mutation m.15923A>G in the MT-TT gene causes mild myopathy – case report of an adult-onset phenotype. BMC Neurology, 18 (1). doi:10.1186/s12883-018-1159-4

Mutation m.15923A>G in the MT-TT gene causes mild myopathy – case report of an adult-onset phenotype

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Author: Kärppä, Mikko1,2,3; Kytövuori, Laura1,2,3; Saari, Markku4;
Organizations: 1Research Unit of Clinical Neuroscience, University of Oulu
2Medical Research Center Oulu, Oulu University Hospital and University of Oulu
3Department of Neurology, Oulu University Hospital
4Turku Centre for Biotechnology, Cell Imaging Core, University of Turku
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.7 MB)
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Language: English
Published: Springer Nature, 2018
Publish Date: 2018-10-23


Background: Only five patients have previously been reported to harbor mutations in the MT-TT gene encoding mitochondrial tRNA threonine. The m.15923A > G mutation has been found in three severely affected children. One of these patients died within days after birth and two had a phenotype of myoclonic epilepsy with ragged red fibers (MERRF) in early childhood. We have now found the mutation in an adult patient with mild myopathy.

Case presentation: The patient is a 64-year-old Finnish man, who developed bilateral ptosis, diplopia and exercise intolerance in his fifties. Family history was unremarkable. Muscle histology showed cytochrome c-oxidase (COX) negative and ragged red fibres. The m.15923A > G mutation heteroplasmy was 33% in the skeletal muscle and 2% in buccal epithelial cells. The mutation was undetectable in the blood. Single-fibre analysis was performed and COX-negative fibres had a substantially higher heteroplasmy of 92%, than the normal fibres in which it was 43%.

Conclusions: We report the fourth patient with m. 15923A > G and with a remarkably milder phenotype than the previous three patients. Our findings and recent biochemical studies suggest that the mutation m.15923A > G is a definite disease-causing mutation. Our results also suggest that heteroplasmy of the m.15923A > G mutation correlates with the severity of the phenotype. This study expands the catalog of the phenotypes caused by mutations in mtDNA.

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Series: BMC neurology
ISSN: 1471-2377
ISSN-E: 1471-2377
ISSN-L: 1471-2377
Volume: 18
Article number: 149
DOI: 10.1186/s12883-018-1159-4
Type of Publication: A1 Journal article – refereed
Field of Science: 3124 Neurology and psychiatry
3111 Biomedicine
Funding: The study was supported by grants from the Sigrid Juselius Foundation, Medical Research Center, University of Oulu and Oulu University Hospital, and State research funding from Oulu University Hospital.
Copyright information: © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.