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Inherited ataxias are a group of heterogeneous disorders in children or adults but their genetic definition remains still undetermined in almost half of the patients. However, CoQ10 deficiency is a rare cause of cerebellar ataxia and ADCK3 is the most frequent gene associated with this defect. We herein report a 48 year old man, who presented with dysarthria and walking difficulties. Brain magnetic resonance imaging showed a marked cerebellar atrophy. Serum lactate was elevated. Tissues obtained by muscle and skin biopsies were studied for biochemical and genetic characterization. Skeletal muscle biochemistry revealed decreased activities of complexes I+III and II+III and a severe reduction of CoQ10 , while skin fibroblasts showed normal CoQ10 levels. A mild loss of maximal respiration capacity was also found by high-resolution respirometry. Molecular studies identified a novel homozygous deletion (c.504del_CT) in ADCK3, causing a premature stop codon. Western blot analysis revealed marked reduction of ADCK3 protein levels. Treatment with CoQ10 was started and, after 1 year follow-up, patient neurological condition slightly improved. This report suggests the importance of investigating mitochondrial function and, in particular, muscle CoQ10 levels, in patients with adult-onset cerebellar ataxia. Moreover, clinical stabilization by CoQ10 supplementation emphasizes the importance of an early diagnosis.

SUCLA2 defects have been associated with mitochondrial DNA (mtDNA) depletion and the triad of hypotonia, dystonia/Leigh-like syndrome, and deafness. A 9-year-old Brazilian boy of consanguineous parents presented with psychomotor delay, deafness, myopathy, ataxia, and chorea. Despite the prominent movement disorder, brain magnetic resonance imaging (MRI) was normal while 1H-magnetic resonance spectroscopy (MRS) showed lactate peaks in the cerebral cortex and lateral ventricles. Decreased biochemical activities of mitochondrial respiratory chain enzymes containing mtDNA-encoded subunits and mtDNA depletion were observed in muscle and fibroblasts. A novel homozygous mutation in SUCLA2, the first one in the ligase coenzyme A (CoA) domain of the protein, was identified. Escalating doses of CoQ10 up to 2000 mg daily were associated with improvement of muscle weakness and stabilization of the disease course. The findings indicate the importance of screening for mitochondrial dysfunction in patients with complex movement disorders without brain MRI lesions and further investigation for potential secondary CoQ10 deficiency in patients with SUCLA2 mutations.

Background: Although causative mutations have been identified for numerous mitochondrial disorders, few disease-modifying treatments are available. Two examples of treatable mitochondrial disorders are coenzyme Q 10 (CoQ 10 or ubiquinone) deficiency and mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). Scope of review: Here, we describe clinical and molecular features of CoQ 10 deficiencies and MNGIE and explain how understanding their pathomechanisms have led to rationale therapies. Primary CoQ 10 deficiencies, due to mutations in genes required for ubiquinone biosynthesis, and secondary deficiencies, caused by genetic defects not directly related to CoQ 10 biosynthesis, often improve with CoQ 10 supplementation. In vitro and in vivo studies of CoQ 10 deficiencies have revealed biochemical alterations that may account for phenotypic differences among patients and variable responses to therapy. In contrast to the heterogeneous CoQ 10 deficiencies, MNGIE is a single autosomal recessive disease due to mutations in the TYMP gene encoding thymidine phosphorylase (TP). In MNGIE, loss of TP activity causes toxic accumulations of the nucleosides thymidine and deoxyuridine that are incorporated by the mitochondrial pyrimidine salvage pathway and cause deoxynucleoside triphosphate pool imbalances, which, in turn cause mtDNA instability. Allogeneic hematopoetic stem cell transplantation to restore TP activity and eliminate toxic metabolites is a promising therapy for MNGIE. Major conclusions: CoQ 10 deficiencies and MNGIE demonstrate the feasibility of treating specific mitochondrial disorders through replacement of deficient metabolites or via elimination of excessive toxic molecules. General significance: Studies of CoQ 10 deficiencies and MNGIE illustrate how understanding the pathogenic mechanisms of mitochondrial diseases can lead to meaningful therapies. This article is part of a Special Issue entitled: Biochemistry of Mitochondria, Life and Intervention 2010. © 2012 Elsevier B.V.

Emmanuele, Valentina et al., © The Author 2014. Published by Oxford University Press. All rights reserved. A member of the four-and-a-half-LIM (FHL) domain protein family, FHL1, is highly expressed in human adult skeletal and cardiac muscle. Mutations in FHL1 have been associated with diverse X-linked muscle diseases: scapuloperoneal (SP) myopathy, reducing body myopathy, X-linked myopathy with postural muscle atrophy, rigid spine syndrome (RSS) and Emery-Dreifuss muscular dystrophy. In 2008, we identified a missense mutation in the second LIM domain of FHL1 (c.365 G>C, p.W122S) in a family with SP myopathy. We generated a knock-in mouse model harboring the c.365 G>C Fhl1 mutation and investigated the effects of this mutation at three time points (3-5 months, 7-10 months and 18-20 months) in hemizygous male and heterozygous female mice. Survival was comparable in mutant and wild-type animals. We observed decreased forelimb strength and exercise capacity in adult hemizygous male mice starting from 7 to 10 months of age. Western blot analysis showed absence of Fhl1 in muscle at later stages. Thus, adult hemizygous male, but not heterozygous female, mice showed a slowly progressive phenotype similar to human patients with late-onset muscle weakness. In contrast to SP myopathy patients with the FHL1 W122S mutation, mutant mice did not manifest cytoplasmic inclusions (reducing bodies) in muscle. Because muscle weakness was evident prior to loss of Fhl1 protein and without reducing bodies, our findings indicate that loss of function is responsible for the myopathy in the Fhl1 W122S knock-in mice., This work has been supported by the Muscular Dystrophy Association (MDA), grant number 115567; and by the Caffarelli Family Study Research (CSFR) Foundation, Inc. L.M.E. and D.S.-G. are supported by the Ramón y Cajal program (PI13/01347), and the Spanish government grants: BFU2011-25734 and PI13/01347.

Autosomal recessive mutations in the thymidine kinase 2 gene (TK2) cause mitochondrial DNA depletion, multiple deletions, or both due to loss of TK2 enzyme activity and ensuing unbalanced deoxynucleotide triphosphate (dNTP) pools. To bypass Tk2 deficiency, we administered deoxycytidine and deoxythymidine monophosphates (dCMP+dTMP) to the Tk2 H126N (Tk2−/−) knock‐in mouse model from postnatal day 4, when mutant mice are phenotypically normal, but biochemically affected. Assessment of 13‐day‐old Tk2−/− mice treated with dCMP+dTMP 200 mg/kg/day each (Tk2−/−200dCMP/dTMP) demonstrated that in mutant animals, the compounds raise dTTP concentrations, increase levels of mtDNA, ameliorate defects of mitochondrial respiratory chain enzymes, and significantly prolong their lifespan (34 days with treatment versus 13 days untreated). A second trial of dCMP+dTMP each at 400 mg/kg/day showed even greater phenotypic and biochemical improvements. In conclusion, dCMP/dTMP supplementation is the first effective pharmacologic treatment for Tk2 deficiency., This work was supported by research grants from the Muscular Dystrophy Association (MH) and the Associazione Malattie Metaboliche Congenite ereditarie (AMMeC) (CG) as well as by the Arturo Estopinan TK2 Research Fund (MH and CG) and the Marriott Mitochondrial Disease Clinic Research Fund (MMDCRF) (MH). MH acknowledges support from NIH grants (P01 HD32062, R01 HD057543, and R01 HD056103 from NICHD) and the Office of Dietary Supplements, as well as U54 NS078059 from NINDS and NICHD. LCL acknowledges support from CEIBioTic‐University of Granada, RYC‐2011‐07643, and RETICEF (Spain).

Balanced pools of deoxyribonucleoside triphosphate precursors are required for DNA replication, and alterations of this balance are relevant to human mitochondrial diseases including mitochondrial neurogastrointestinal encephalopathy. In this disease, autosomal recessive TYMP mutations cause severe reductions of thymidine phosphorylase activity; marked elevations of the pyrimidine nucleosides thymidine and deoxyuridine in plasma and tissues, and somatic multiple deletions, depletion and site-specific point mutations of mitochondrial DNA. Thymidine phosphorylase and uridine phosphorylase double knockout mice recapitulated several features of these patients including thymidine phosphorylase activity deficiency, elevated thymidine and deoxyuridine in tissues, mitochondrial DNA depletion, respiratory chain defects and white matter changes. However, in contrast to patients with this disease, mutant mice showed mitochondrial alterations only in the brain. To test the hypothesis that elevated levels of nucleotides cause unbalanced deoxyribonucleoside triphosphate pools and, in turn, pathogenic mitochondrial DNA instability, we have stressed double knockout mice with exogenous thymidine and deoxyuridine, and assessed clinical, neuroradiological, histological, molecular, and biochemical consequences. Mutant mice treated with exogenous thymidine and deoxyuridine showed reduced survival, body weight, and muscle strength, relative to untreated animals. Moreover, in treated mutants, leukoencephalopathy, a hallmark of the disease, was enhanced and the small intestine showed a reduction of smooth muscle cells and increased fibrosis. Levels of mitochondrial DNA were depleted not only in the brain but also in the small intestine, and deoxyribonucleoside triphosphate imbalance was observed in the brain. The relative proportion, rather than the absolute amount of deoxyribonucleoside triphosphate, was critical for mitochondrial DNA maintenance. Thus, our results demonstrate that stress of exogenous pyrimidine nucleosides enhances the mitochondrial phenotype of our knockout mice. Our mouse studies provide insights into the pathogenic role of thymidine and deoxyuridine imbalance in mitochondrial neurogastrointestinal encephalopathy and an excellent model to study new therapeutic approaches. © 2014 The Author (2014). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved.

Primary human CoQ10 deficiencies are clinically heterogeneous diseases caused by mutations in PDSS2 and other genes required for CoQ10 biosynthesis. Our in vitro studies of PDSS2 mutant fibroblasts, with