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  • Hanninen, Reetta L.; Ahonen, Saija; Marquez, Merce; Myohanen, Maarit J.; Hytonen, Marjo K.; Lohi, Hannes (2015)
    Mitochondrial DNA depletion syndromes (MDS) are often serious autosomal recessively inherited disorders characterized by tissue-specific mtDNA copy number reduction. Many genes, including MPV17, are associated with the hepatocerebral form of MDS. MPV17 encodes for a mitochondrial inner membrane protein with a poorly characterized function. Several MPV17 mutations have been reported in association with a heterogeneous group of early-onset manifestations, including liver disease and neurological problems. Mpv17-deficient mice present renal and hearing defects. We describe here a MPV17 truncation mutation in dogs. We found a 1-bp insertion in exon 4 of the MPV17 gene, resulting in a frameshift and early truncation of the encoded protein. The mutation halves MPV17 expression in the lymphocytes of the homozygous dogs and the truncated protein is not translated in transfected cells. The insertion mutation is recurrent and exists in many unrelated breeds, although is highly enriched in the Boxer breed. Unexpectedly, despite the truncation of MPV17, we could not find any common phenotypes in the genetically affected dogs. The lack of observable phenotype could be due to a late onset, mild symptoms or potential tissue-specific compensatory mechanisms. This study suggests species-specific differences in the manifestation of the MPV17 defects and establishes a novel large animal model to further study MPV17 function and role in mitochondrial biology.
  • Garone, Caterina; Taylor, Robert W.; Nascimento, Andres; Poulton, Joanna; Fratter, Carl; Dominguez-Gonzalez, Cristina; Evans, Julie C.; Loos, Mariana; Isohanni, Pirjo; Suomalainen, Anu; Ram, Dipak; Hughes, M. Imelda; McFarland, Robert; Barca, Emanuele; Gomez, Carlos Lopez; Jayawant, Sandeep; Thomas, Neil D.; Manzur, Adnan Y.; Kleinsteuber, Karin; Martin, Miguel A.; Kerr, Timothy; Gorman, Grainne S.; Sommerville, Ewen W.; Chinnery, Patrick F.; Hofer, Monika; Karch, Christoph; Ralph, Jeffrey; Camara, Yolanda; Madruga-Garrido, Marcos; Dominguez-Carral, Jana; Ortez, Carlos; Emperador, Sonia; Montoya, Julio; Chakrapani, Anupam; Kriger, Joshua F.; Schoenaker, Robert; Levin, Bruce; Thompson, John L. P.; Long, Yuelin; Rahman, Shamima; Donati, Maria Alice; DiMauro, Salvatore; Hirano, Michio (2018)
    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.