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Retrospective natural history of thymidine kinase 2 deficiency

Lookup NU author(s): Professor Robert Taylor, Professor Bobby McFarland, Professor Grainne Gorman, Dr Ewen Sommerville, Professor Patrick Chinnery

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted. Background: Thymine kinase 2 (TK2) is a mitochondrial matrix protein encoded in nuclear DNA and phosphorylates the pyrimidine nucleosides: thymidine and deoxycytidine. Autosomal recessive TK2 mutations cause a spectrum of disease from infantile onset to adult onset manifesting primarily as myopathy. Objective: To perform a retrospective natural history study of a large cohort of patients with TK2 deficiency. Methods: The study was conducted by 42 investigators across 31 academic medical centres. Results: We identified 92 patients with genetically confirmed diagnoses of TK2 deficiency: 67 from literature review and 25 unreported cases. Based on clinical and molecular genetics findings, we recognised three phenotypes with divergent survival: (1) infantile-onset myopathy (42.4%) with severe mitochondrial DNA (mtDNA) depletion, frequent neurological involvement and rapid progression to early mortality (median post-onset survival (POS) 1.00, CI 0.58 to 2.33 years); (2) childhood-onset myopathy (40.2%) with mtDNA depletion, moderate-to-severe progression of generalised weakness and median POS at least 13 years; and (3) late-onset myopathy (17.4%) with mild limb weakness at onset and slow progression to respiratory insufficiency with median POS of 23 years. Ophthalmoparesis and facial weakness are frequent in adults. Muscle biopsies show multiple mtDNA deletions often with mtDNA depletion. Conclusions: In TK2 deficiency, age at onset, rate of weakness progression and POS are important variables that define three clinical subtypes. Nervous system involvement often complicates the clinical course of the infantile-onset form while extraocular muscle and facial involvement are characteristic of the late-onset form. Our observations provide essential information for planning future clinical trials in this disorder.


Publication metadata

Author(s): Garone C, Taylor RW, Nascimento A, Poulton J, Fratter C, Dominguez-Gonzalez C, Evans JC, Loos M, Isohanni P, Suomalainen A, Ram D, Hughes MI, McFarland R, Barca E, Lopez Gomez C, Jayawant S, Thomas ND, Manzur AY, Kleinsteuber K, Martin MA, Kerr T, Gorman GS, Sommerville EW, Chinnery PF, Hofer M, Karch C, Ralph J, Camara Y, Madruga-Garrido M, Dominguez-Carral J, Ortez C, Emperador S, Montoya J, Chakrapani A, Kriger JF, Schoenaker R, Levin B, Thompson JLP, Long Y, Rahman S, Donati MA, Dimauro S, Hirano M

Publication type: Article

Publication status: Published

Journal: Journal of Medical Genetics

Year: 2018

Volume: 55

Issue: 8

Pages: 515-521

Print publication date: 01/08/2018

Online publication date: 30/03/2018

Acceptance date: 11/03/2018

Date deposited: 19/07/2018

ISSN (print): 0022-2593

ISSN (electronic): 1468-6244

Publisher: BMJ Publishing Group

URL: https://doi.org/10.1136/jmedgenet-2017-105012

DOI: 10.1136/jmedgenet-2017-105012

PubMed id: 29602790


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