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Funder: Kay Kendall Leukaemia Fund (KKLF); doi: https://doi.org/10.13039/501100000402, Funder: EC | EC Seventh Framework Programm | FP7 People: Marie-Curie Actions (FP7-PEOPLE - Specific Programme "People" Implementing the Seventh Framework Programme of the European Community for Research, Technological Development and Demonstration Activities (2007 to 2013)); doi: https://doi.org/10.13039/100011264; Grant(s): Mitobiopath-705560, Many cellular processes, including ribosome biogenesis, are regulated through post-transcriptional RNA modifications. Here, a genome-wide analysis of the human mitochondrial transcriptome shows that 2'-O-methylation is limited to residues of the mitoribosomal large subunit (mtLSU) 16S mt-rRNA, introduced by MRM1, MRM2 and MRM3, with the modifications installed by the latter two proteins being interdependent. MRM2 controls mitochondrial respiration by regulating mitoribosome biogenesis. In its absence, mtLSU particles (visualized by cryo-EM at the resolution of 2.6 ��) present disordered RNA domains, partial occupancy of bL36m and bound MALSU1:L0R8F8:mtACP anti-association module, allowing five mtLSU biogenesis intermediates with different intersubunit interface configurations to be placed along the assembly pathway. However, mitoribosome biogenesis does not depend on the methyltransferase activity of MRM2. Disruption of the MRM2 Drosophila melanogaster orthologue leads to mitochondria-related developmental arrest. This work identifies a key checkpoint during mtLSU assembly, essential to maintain mitochondrial homeostasis.

Patients with mitochondrial diseases, who usually manifest a multisystem disease, are considered potentially at-risk for a severe coronavirus disease 2019 (COVID-19). The objective of this study is to analyze the clinical features, prognosis and outcomes of COVID-19 in patients with primary mitochondrial diseases in a cohort of patients followed in Italy. We searched for patients with primary mitochondrial diseases and COVID-19 followed by the Italian Collaborative Network of Mitochondrial Diseases. In a total of 1843 patients followed by the National Network, we have identified from March 1st to January 30th, 2021, 27 SARS-CoV-2 infection. Most of the patients were pauci or asymptomatic (85%) and treated at home. The most common signs of COVID-19 were fever (78,9%), fatigue (47,4%), myalgia (42,1%), cough and headache (36,8%), and dyspnea (31,6%). Those who required COVID-19 therapy were treated with low-molecular-weight heparin, glucocorticoids, and antibiotics (mainly azithromycin) without serious side effects related to the therapy. Five patients (18,5%) clinically deteriorated during the infection, and one of them died for pneumonia. Primary mitochondrial diseases infected individuals seemed to be similarly affected by SARS-CoV-2 compared with the general Italian population in terms of clinical presentation and outcome.

Cellular Indexing of Transcriptomes and Epitopes by Sequencing (CITE-seq) is a recently established multimodal single cell analysis technique combining the immunophenotyping capabilities of antibody labeling and cell sorting with the resolution of single-cell RNA sequencing (scRNA-seq). By simply adding a 12-bp nucleotide barcode to antibodies (cell hashing), CITE-seq can be used to sequence antibody-bound tags alongside the cellular mRNA, thus reducing costs of scRNA-seq by performing it at the same time on multiple barcoded samples in a single run. Here, we illustrate an ideal CITE-seq data analysis workflow by characterizing the transcriptome of SH-SY5Y neuroblastoma cell line, a widely used model to study neuronal function and differentiation. We obtained transcriptomes from a total of 2879 single cells, measuring an average of 1600 genes/cell. Along with standard scRNA-seq data handling procedures, such as quality checks and cell filtering procedures, we performed exploratory analyses to identify most stable genes to be possibly used as reference housekeeping genes in qPCR experiments. We also illustrate how to use some popular R packages to investigate cell heterogeneity in scRNA-seq data, namely Seurat, Monocle, and slalom. Both the CITE-seq dataset and the code used to analyze it are freely shared and fully reusable for future research.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive disease caused by thymidine phosphorylase (TP) enzyme defect. As gastrointestinal changes do not revert in patients undergone TP replacement therapy, one can postulate that other unexplored mechanisms contribute to MNGIE pathophysiology. Hence, we focused on the local TP angiogenic potential that has never been considered in MNGIE. In this study, we investigated the enteric submucosal microvasculature and the effect of hypoxia on fibrosis and enteric neurons density in jejunal full-thickness biopsies collected from patients with MNGIE. Orcein staining was used to count blood vessels based on their size. Fibrosis was assessed using the Sirius Red and Fast Green method. Hypoxia and neoangiogenesis were determined via hypoxia-inducible-factor-1α (HIF-1α) and vascular endothelial cell growth factor (VEGF) protein expression, respectively. Neuron-specific enolase was used to label enteric neurons. Compared with controls, patients with MNGIE showed a decreased area of vascular tissue, but a twofold increase of submucosal vessels/mm(2) with increased small size and decreased medium and large size vessels. VEGF positive vessels, fibrosis index, and HIF-1α protein expression were increased, whereas there was a diminished thickness of the longitudinal muscle layer with an increased interganglionic distance and reduced number of myenteric neurons. We demonstrated the occurrence of an angiopathy in the GI tract of patients with MNGIE. Neoangiogenetic changes, as detected by the abundance of small size vessels in the jejunal submucosa, along with hypoxia provide a morphological basis to explain neuromuscular alterations, vasculature breakdown, and ischemic abnormalities in MNGIE. NEW & NOTEWORTHY Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is characterized by a genetically driven defect of thymidine phosphorylase, a multitask enzyme playing a role also in angiogenesis. Indeed, major gastrointestinal bleedings are life-threatening complications of MNGIE. Thus, we focused on jejunal submucosal vasculature and showed intestinal microangiopathy as a novel feature occurring in this disease. Notably, vascular changes were associated with neuromuscular abnormalities, which may explain gut dysfunction and help to develop future therapeutic approaches in MNGIE.

Expression of human mitochondrial DNA is indispensable for proper function of the oxidative phosphorylation machinery. The mitochondrial genome encodes 22 tRNAs, 2 rRNAs and 11 mRNAs and their post-transcriptional modification constitutes one of the key regulatory steps during mitochondrial gene expression. Cytosine-5 methylation (m5C) has been detected in mitochondrial transcriptome, however its biogenesis has not been investigated in details. Mammalian NOP2/Sun RNA Methyltransferase Family Member 2 (NSUN2) has been characterized as an RNA methyltransferase introducing m5C in nuclear-encoded tRNAs, mRNAs and microRNAs and associated with cell proliferation and differentiation, with pathogenic variants in NSUN2 being linked to neurodevelopmental disorders. Here we employ spatially restricted proximity labelling and immunodetection to demonstrate that NSUN2 is imported into the matrix of mammalian mitochondria. Using three genetic models for NSUN2 inactivation—knockout mice, patient-derived fibroblasts and CRISPR/Cas9 knockout in human cells—we show that NSUN2 is necessary for the generation of m5C at positions 48, 49 and 50 of several mammalian mitochondrial tRNAs. Finally, we show that inactivation of NSUN2 does not have a profound effect on mitochondrial tRNA stability and oxidative phosphorylation in differentiated cells. We discuss the importance of the newly discovered function of NSUN2 in the context of human disease.

NUBPL (Nucleotide-binding protein like) protein encodes a member of the Mrp/NBP35 ATP-binding proteins family, deemed to be involved in mammalian complex I (CI) assembly process. Exome sequencing of a patient presenting with infantile-onset hepatopathy, renal tubular acidosis, developmental delay, short stature, leukoencephalopathy with minimal cerebellar involvement and multiple OXPHOS deficiencies revealed the presence of two novel pathogenic compound heterozygous variants in NUBPL (p.Phe242Leu/p.Leu104Pro). We investigated patient's and control immortalised fibroblasts and demonstrated that both the peripheral and the membrane arms of complex I are undetectable in mutant NUBPL cells, resulting in virtually absent CI holocomplex and loss of enzyme activity. In addition, complex III stability was moderately affected as well. Lentiviral-mediated expression of the wild-type NUBPL cDNA rescued both CI and CIII assembly defects, confirming the pathogenicity of the variants. In conclusion, this is the first report describing a complex multisystemic disorder due to NUBPL defect. In addition, we confirmed the role of NUBPL in Complex I assembly associated with secondary effect on Complex III stability and we demonstrated a defect of mtDNA-related translation which suggests a potential additional role of NUBPL in mtDNA expression.

Mitochondrial maintenance disorders present as a spectrum ranging from severe infantile multisystemic syndrome to childhood or adult tissue-specific diseases. Hallmark is the variable association of qualitative (point mutations, multiple deletions) or quantitative (copy number reduction) molecular genetic defect of mitochondrial DNA (mtDNA), biochemical dysfunction with multiple OXPHOS defects and morphological alterations of the mitochondrial network. Therapies for mitochondrial disorders, targeting pathogenic mechanism with “general” or “disease tailored” action, have been successfully experimented in in vitro and in vivo studies. Preclinical evidence of efficacy and safety has led for some of them to the translation into clinical trials. Those are specifically available for treatment in mtDNA maintenance disorders, bringing the hope to find a definitive cure in the immediate future. In this chapter, we will present an overview of the clinical syndrome in the mtDNA replication pathway and will elucidate the potential application of pharmacological approaches with general action to mtDNA maintenance disorders by analyzing compounds increasing mitochondrial biogenesis or modulating mTOR pathway. In addition, we will explore supplementation of nucleosides, clearance of toxic metabolites and enzyme replacement therapies in enzymatic deficiencies and gene therapy approaches in the same pathway.

Defects in nuclear-encoded proteins of the mitochondrial translation machinery cause early-onset and tissue-specific deficiency of one or more OXPHOS complexes. Here, we report a 7-year-old Italian boy with childhood-onset rapidly progressive encepha- lomyopathy and stroke-like episodes. Multiple OXPHOS defects and decreased mtDNA copy number (40%) were detected in muscle homogenate. Clinical features combined with low level of plasma citrulline were highly suggestive of mitochondrial en- cephalopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome, however, the common m.3243 A > G mutation was ex- cluded. Targeted exome sequencing of genes encoding the mitochondrial proteome identified a damaging mutation, c.567 G > A, affecting a highly conserved amino acid residue (p.Gly189Arg) of the MRM2 protein. MRM2 has never before been linked to a hu- man disease and encodes an enzyme responsible for 2’-O-methyl modification at position U1369 in the human mitochondrial 16S rRNA. We generated a knockout yeast model for the orthologous gene that showed a defect in respiration and the reduction of the 2’-O-methyl modification at the equivalent position (U2791) in the yeast mitochondrial 21S rRNA. Complementation with the mrm2 allele carrying the equivalent yeast mutation failed to rescue the respiratory phenotype, which was instead com- pletely rescued by expressing the wild-type allele. Our findings establish that defective MRM2 causes a MELAS-like phenotype, and suggests the genetic screening of the MRM2 gene in patients with a m.3243 A > G negative MELAS-like presentation.

Objective Thymidine kinase 2 (TK2), a critical enzyme in the mitochondrial pyrimidine salvage pathway, is essential for mitochondrial DNA (mtDNA) maintenance. Mutations in the nuclear gene, TK2, cause TK2 deficiency, which manifests predominantly in children as myopathy with mtDNA depletion. Molecular bypass therapy with the TK2 products, deoxycytidine monophosphate (dCMP) and deoxythymidine monophosphate (dTMP), prolongs the life span of Tk2-deficient (Tk2–/–) mice by 2- to 3-fold. Because we observed rapid catabolism of the deoxynucleoside monophosphates to deoxythymidine (dT) and deoxycytidine (dC), we hypothesized that: (1) deoxynucleosides might be the major active agents and (2) inhibition of deoxycytidine deamination might enhance dTMP+dCMP therapy. Methods To test these hypotheses, we assessed two therapies in Tk2–/– mice: (1) dT+dC and (2) coadministration of the deaminase inhibitor, tetrahydrouridine (THU), with dTMP+dCMP. Results We observed that dC+dT delayed disease onset, prolonged life span of Tk2-deficient mice and restored mtDNA copy number as well as respiratory chain enzyme activities and levels. In contrast, dCMP+dTMP+THU therapy decreased life span of Tk2–/– animals compared to dCMP+dTMP. Interpretation Our studies demonstrate that deoxynucleoside substrate enhancement is a novel therapy, which may ameliorate TK2 deficiency in patients. Ann Neurol 2017;81:641–652

[Objective] Thymidine kinase 2, encoded by the nuclear gene TK2, is required for mitochondrial DNA maintenance. Autosomal recessive TK2 mutations cause depletion and multiple deletions of mtDNA that manifest predominantly as a myopathy usually beginning in childhood and progressing relentlessly. We investigated the safety and efficacy of deoxynucleoside monophosphate and deoxynucleoside therapies., [Methods] We administered deoxynucleoside monophosphates and deoxynucleoside to 16 TK2‐deficient patients under a compassionate use program., [Results] In 5 patients with early onset and severe disease, survival and motor functions were better than historically untreated patients. In 11 childhood and adult onset patients, clinical measures stabilized or improved. Three of 8 patients who were nonambulatory at baseline gained the ability to walk on therapy; 4 of 5 patients who required enteric nutrition were able to discontinue feeding tube use; and 1 of 9 patients who required mechanical ventilation became able to breathe independently. In motor functional scales, improvements were observed in the 6‐minute walk test performance in 7 of 8 subjects, Egen Klassifikation in 2 of 3, and North Star Ambulatory Assessment in all 5 tested. Baseline elevated serum growth differentiation factor 15 levels decreased with treatment in all 7 patients tested. A side effect observed in 8 of the 16 patients was dose‐dependent diarrhea, which did not require withdrawal of treatment. Among 12 other TK2 patients treated with deoxynucleoside, 2 adults developed elevated liver enzymes that normalized following discontinuation of therapy., [Interpretation] This open‐label study indicates favorable side effect profiles and clinical efficacy of deoxynucleoside monophosphate and deoxynucleoside therapies for TK2 deficiency. ANN NEUROL 2019;86:293–303, This work was supported in part by grants from the Spanish Carlos III Health Institute (PMP15/00025 for C.P., F.Ma., and R.M.; PI16/00579 and CP09/00011 for C.J.‐M.), Muscular Dystrophy Association (577391), Arturo Estopinan TK2 Research Fund, Generalitat de Catalunya PERIS program (SLT002/16/00370 for J.T‐T.), and European Regional Development Fund.

BackgroundThymine 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.ObjectiveTo perform a retrospective natural history study of a large cohort of patients with TK2 deficiency.MethodsThe study was conducted by 42 investigators across 31 academic medical centres.ResultsWe 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.ConclusionsIn 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.

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.

ATPase family AAA-domain containing protein 3A (ATAD3A) is a nuclear-encoded mitochondrial membrane protein implicated in mitochondrial dynamics, nucleoid organization, protein translation, cell growth, and cholesterol metabolism. We identified a recurrent de novo ATAD3A c.1582C>T (p.Arg528Trp) variant by whole-exome sequencing (WES) in five unrelated individuals with a core phenotype of global developmental delay, hypotonia, optic atrophy, axonal neuropathy, and hypertrophic cardiomyopathy. We also describe two families with biallelic variants in ATAD3A, including a homozygous variant in two siblings, and biallelic ATAD3A deletions mediated by nonallelic homologous recombination (NAHR) between ATAD3A and gene family members ATAD3B and ATAD3C. Tissue-specific overexpression of borR534W, the Drosophila mutation homologous to the human c.1582C>T (p.Arg528Trp) variant, resulted in a dramatic decrease in mitochondrial content, aberrant mitochondrial morphology, and increased autophagy. Homozygous null bor larvae showed a significant decrease of mitochondria, while overexpression of borWT resulted in larger, elongated mitochondria. Finally, fibroblasts of an affected individual exhibited increased mitophagy. We conclude that the p.Arg528Trp variant functions through a dominant-negative mechanism that results in small mitochondria that trigger mitophagy, resulting in a reduction in mitochondrial content. ATAD3A variation represents an additional link between mitochondrial dynamics and recognizable neurological syndromes, as seen with MFN2, OPA1, DNM1L, and STAT2 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.

Mitochondrial neurogastrointestinal encephalomyopathy is a rare multisystemic autosomic recessive disorder characterized by: onset typically before the age of 30 years; ptosis; progressive external ophthalmoplegia; gastrointestinal dysmotility; cachexia; peripheral neuropathy; and leucoencephalopathy. The disease is caused by mutations in the TYMP gene encoding thymidine phosphorylasethymine phosphorylase. Anecdotal reports suggest that allogeneic haematopoetic stem cell transplantation may be beneficial for mitochondrial neurogastrointestinal encephalomyopathy, but is associated with a high mortality. After selecting patients who fulfilled the clinical criteria for mitochondrial neurogastrointestinal encephalomyopathy and had severe thymidine phosphorylase deficiency in the buffy coat (G in Europe and c.518T>G in the Dominican Republic, that could guide genetic screening in each location. Although the sequence of clinical manifestations in the disease varied, half of the patients initially had gastrointestinal symptoms. We confirmed anecdotal reports of intra- and inter-familial clinical variability and absence of genotype–phenotype correlation in the disease, suggesting genetic modifiers, environmental factors or both contribute to disease manifestations. Acute medical events such as infections often provoked worsening of symptoms, suggesting that careful monitoring and early treatment of intercurrent illnesses may be beneficial. We observed endocrine/exocrine pancreatic insufficiency, which had not previously been reported. Kaplan–Meier analysis revealed significant mortality between the ages of 20 and 40 years due to infectious or metabolic complications. Despite increasing awareness of this illness, a high proportion of patients had been misdiagnosed. Early and accurate diagnosis of mitochondrial neurogastrointestinal encephalomyopathy, together with timely treatment of acute intercurrent illnesses, may retard disease progression and increase the number of patients eligible for allogeneic haematopoetic stem cell transplantation.

In this review, we trace the origins and follow the development of mitochondrial medicine from the premolecular era (1962-1988) based on clinical clues, muscle morphology, and biochemistry into the molecular era that started in 1988 and is still advancing at a brisk pace. We have tried to stress conceptual advances, such as endosymbiosis, uniparental inheritance, intergenomic signaling and its defects, and mitochondrial dynamics. We hope that this historical review also provides an update on mitochondrial medicine, although we fully realize that the speed of progress in this area makes any such endeavor akin to writing on water. © 2010 Wiley-Liss, Inc.

Aim To describe a spectrum of intracerebral large artery disease in Aicardi–Goutieres syndrome (AGS) associated with mutations in the AGS5 gene SAMHD1. Method We used clinical and radiological description and molecular analysis. Results Five individuals (three males, two females) were identified as having biallelic mutations in SAMHD1 and a cerebral arteriopathy in association with peripheral vessel involvement resulting in chilblains and ischaemic ulceration. The cerebral vasculopathy was primarily occlusive in three patients (with terminal carotid occlusion and basal collaterals reminiscent of moyamoya syndrome) and aneurysmal in two. Three of the five patients experienced intracerebral haemorrhage, which was fatal in two individuals. Post-mortem examination of one patient suggested that the arteriopathy was inflammatory in origin. Interpretation Mutations in SAMHD1 are associated with a cerebral vasculopathy which is likely to have an inflammatory aetiology. A similar disease has not been observed in patients with mutations in AGS1 to AGS4, suggesting a particular role for SAMHD1 in vascular homeostasis. Our report raises important questions about the management of patients with mutations in SAMHD1.

Following a previous preliminary report on a group of children suffering from partial epilepsies, we present the final considerations on the same group in order to evaluate the long-term efficacy, tolerability and safety of oxcarbazepine (OXC). We enrolled 36 patients (mean age 8.5), between January 2003 and December 2004, with new diagnosis of partial epilepsy: 25 patients were affected by idiopathic partial epilepsy, eight by symptomatic epilepsy and three by cryptogenic epilepsy. Each patient was scheduled to attend the center four times after the initial examination: 3 months (T1), 12 months (T2), 24 (T3) months and 36 (T4) months after the beginning of OXC-monotherapy (T0). At the end of our study, 20 patients were seizure free (SF): nine stopped OXC because of SF for at least 2 years, 11 were still on therapy. One patient showed a reduction of seizure frequency >or=50%, three were non responders (but still on therapy), nine stopped OXC due to a non-responder condition during follow-up before T4 and one because of adverse effects. At the end of the study no EEG focal abnormalities became generalized because of treatment. Normalization of EEG was observed in ten patients. Our preliminary findings have been confirmed. OXC can be considered an effective and well tolerated first line drug for long-term monotherapy in children with epilepsy, both for idiopathic and symptomatic/cryptogenic forms.

The present controlled study aims to evaluate topiramate (TPM) effect on total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein, very low-density lipoprotein, apolipoproteins A1, B and lipoprotein (a). Seventy patients in evolving age suffering from various types of epilepsy, treated with TPM, (age range: 6 months-22 years) were evaluated before and after 12 months of treatment and compared with 110 sex- and age-matched subjects. At baseline, no significant difference was present between controls and children treated with TPM. After a year, the BMI did not show significant change in adults and remained into respective growth curve. No significant difference in lipids and lipoproteins neither between first and second evaluation nor between patients and controls was found. Some intra-group variation has been noticed: whilst controls maintained similar levels, the 70 patients on TPM monotherapy showed a slight decrease in TC, triglycerides and HDL. These fluctuations, however, occurred in the normal range so neither dietary nor pharmacological treatment of hyperlipidaemia after a year of TPM was necessary.

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.

The transport and intracellular trafficking of heme biosynthesis intermediates are crucial for hemoglobin production, which is a critical process in developing red cells. Here, we profiled gene expression in terminally differentiating murine fetal liver-derived erythroid cells to identify regulators of heme metabolism. We determined that TMEM14C, an inner mitochondrial membrane protein that is enriched in vertebrate hematopoietic tissues, is essential for erythropoiesis and heme synthesis in vivo and in cultured erythroid cells. In mice, TMEM14C deficiency resulted in porphyrin accumulation in the fetal liver, erythroid maturation arrest, and embryonic lethality due to profound anemia. Protoporphyrin IX synthesis in TMEM14C-deficient erythroid cells was blocked, leading to an accumulation of porphyrin precursors. The heme synthesis defect in TMEM14C-deficient cells was ameliorated with a protoporphyrin IX analog, indicating that TMEM14C primarily functions in the terminal steps of the heme synthesis pathway. Together, our data demonstrate that TMEM14C facilitates the import of protoporphyrinogen IX into the mitochondrial matrix for heme synthesis and subsequent hemoglobin production. Furthermore, the identification of TMEM14C as a protoporphyrinogen IX importer provides a genetic tool for further exploring erythropoiesis and congenital anemias.

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.

Spinal muscular atrophy is a common motor neuron disease caused by low survival motoneuron (SMN), a key protein in the proper splicing of genes. Restoring the protein is therefore a promising therapeutic strategy. Implementation of this strategy, however, depends on defining the temporal requirements for SMN. Here, we used controlled knockdown of SMN in transgenic mice to determine the precise postnatal stage requirements for this protein. Reducing SMN in neonatal mice resulted in a classic SMA-like phenotype. Unexpectedly, depletion of SMN in adults had relatively little effect. Insensitivity to low SMN emerged abruptly at postnatal day 17, which coincided with establishment of the fully mature neuromuscular junction (NMJ). Mature animals depleted of SMN eventually exhibited evidence of selective neuromuscular pathology that was made worse by traumatic injury. The ability to regenerate the mature NMJ in aged or injured SMN-depleted mice was grossly impaired, a likely consequence of the inability to meet the surge in demand for motoneuronal SMN that was seen in controls. Our results demonstrate that relative maturity of the NMJ determines the temporal requirement for the SMN protein. These observations suggest that the use of potent but potentially deleterious SMN-enhancing agents could be tapered in human patients once the neuromuscular system matures and reintroduced as needed to enhance SMN for remodeling aged or injured NMJs. © Copyright 2014 American Society for Clinical Investigation.

PURPOSE: The aim of the present study was to assess serum lipid levels before and after treatment with oxcarbazepine in children with epilepsy. METHODS: We measured total cholesterol (TC), triglycerides (TGs) and high-density lipoprotein cholesterol (HDL-C) in 28 patients whereas only TC levels in 11 patients, during baseline period and at 3 months after the beginning of therapy with oxcarbazepine. RESULTS: During baseline period, median values were: 4.38 (IQR=4.12-5.03) mmol/L for TC levels, 1.72(IQR=1.42-2.01) mmol/L for HDL-C levels and 1.54 (IQR=1.29-1.96) mmol/L for TGs levels. At three months, median values were: 4.38 (4.10-4.95) mmol/L for TC levels (p

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

The molecular diagnosis of mitochondrial disorders still remains elusive in a large proportion of patients, but advances in next generation sequencing are significantly improving our chances to detect mutations even in sporadic patients. Syndromes associated with mitochondrial DNA multiple deletions are caused by different molecular defects resulting in a wide spectrum of predominantly adult-onset clinical presentations, ranging from progressive external ophthalmoplegia to multi-systemic disorders of variable severity. The mutations underlying these conditions remain undisclosed in half of the affected subjects. We applied next-generation sequencing of known mitochondrial targets (MitoExome) to probands presenting with adult-onset mitochondrial myopathy and harbouring mitochondrial DNA multiple deletions in skeletal muscle. We identified autosomal recessive mutations in the DGUOK gene (encoding mitochondrial deoxyguanosine kinase), which has previously been associated with an infantile hepatocerebral form of mitochondrial DNA depletion. Mutations in DGUOK occurred in five independent subjects, representing 5.6% of our cohort of patients with mitochondrial DNA multiple deletions, and impaired both muscle DGUOK activity and protein stability. Clinical presentations were variable, including mitochondrial myopathy with or without progressive external ophthalmoplegia, recurrent rhabdomyolysis in a young female who had received a liver transplant at 9 months of age and adult-onset lower motor neuron syndrome with mild cognitive impairment. These findings reinforce the concept that mutations in genes involved in deoxyribonucleotide metabolism can cause diverse clinical phenotypes and suggest that DGUOK should be screened in patients harbouring mitochondrial DNA deletions in skeletal muscle. © 2012 The Author (2012). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Summary Two major groups of inborn errors of energy metabolism are reviewed –glycogenoses and defects of the mitochondrial respiratory chain – to see how often these disorders present in fetal life or neonatally. After some general considerations on energy metabolism in the pre- and postnatal development of the human infant, different glycogen storage diseases and mitochondrial encephalomyopathies are surveyed. General conclusions are that: (i) disorders of glycogen metabolism are more likely to cause ‘fetal disease' than defects of the respiratory chain; (ii) mitochondrial encephalomyopathies, especially those due to defects of the nuclear genome, are frequent causes of neonatal or infantile diseases, typically Leigh syndrome, but usually do not cause fetal distress; (iii) notable exceptions include mutations in the complex III assembly gene BCS1L resulting in the GRACILE syndrome (growth retardation, aminoaciduria, cholestasis, iron overload, lactic acidosis, and early death), and defects of mitochondrial protein synthesis, which are the ‘new frontier' in mitochondrial translational research.

Homozygous mutations in the gene for fatty acid 2-hydroxylase (FA2H) have been associated in humans with three neurodegenerative disorders: complicated spastic paraplegia (SPG35), leukodystrophy with spastic paraparesis and dystonia, and neurodegeneration with brain iron accumulation. Here, we describe a novel homozygous c.270+3A>T mutation in an Italian consanguineous family. In two affected brothers (age at molecular diagnosis 22y and 15y; age at last follow-up 24y and 17y), altered FA2H function led to a severe phenotype, with clinical features overlapping those of the three FA2H-associated disorders. Both patients showed childhood onset progressive spastic paraparesis, mild pyramidal and cerebellar upper limb signs, severe cognitive impairment, white-matter disease, and cerebellar, brainstem, and spinal cord atrophy. However, absence of dystonia, drowsiness episodes, and a subtle globus pallidus involvement suggested that FA2H mutations result in a clinical spectrum, rather than causing distinct disorders. Although clinical heterogeneity is apparent, larger numbers of patients are needed to establish more accurate genotype-phenotype correlations. © The Authors. Developmental Medicine & Child Neurology © 2011 Mac Keith Press.

We consider recent developments in disorders affecting three areas of metabolism: glycogen, fatty acids, and the mitochondrial respiratory chain. Among the glycogenoses, new attention has been directed to defects of glycogen synthesis resulting in absence rather than excess of muscle glycogen ("aglycogenosis"). These include defects of glycogen synthetase and defects of glycogenin, the primer of glycogen synthesis. Considerable progress also has been made in our understanding of alterations of glycogen metabolism that result in polyglucosan storage. Among the disorders of lipid metabolism, mutations in the genes encoding two triglyceride lipases acting hand in hand cause severe generalized lipid storage myopathy, one associated with ichthyosis (Chanarin-Dorfman syndrome), the other dominated by juvenile-onset weakness. For the mitochondrial myopathies, we discuss the importance of homoplasmic mitochondrial DNA mutations and review the rapid progress made in our understanding of the coenzyme Q10 deficiencies, which are often treatable. © Springer Science+Business Media, LLC 2010.

We report a new case of infantile idiopathic hemiconvulsion-hemiplegia syndrome (HH). A prolonged right-sided febrile convulsion was followed 4 days later, by right hemiconvulsive status epilepticus, documented by video-electroencephalogram (EEG) recording. The child developed an ipsilateral hemiplegia, partially improved during the first month of follow-up. Sequential cerebral magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (1H-MRS) at 6, 15, 30 days of follow-up showed a cytotoxic edema in the left hemisphere and a subsequent necrosis. At 1-year of follow-up, we performed MRI control because of febrile convulsion lasting few minutes that confirmed a non-progressive left hemisphere atrophy. After 2 years, the patient was seizure-free, with a mild right hemiplegia and language skills deficit. We discuss the unclear pathogenesis of HH through sequential neuroradiological evaluation.

Congenital Cataracts with Facial Dysmorphisms and Neuropathy (CCFDN) is a complex autosomal recessive disorder characterized by bilateral congenital cataracts, developmental delay, peripheral; hypo-demyelinating neuropathy, mild facial dysmorphisms, and other rare signs. Cerebral and spinal cord atrophy is the main neuroimaging finding but other less common abnormalities have been previously described. We describe progressive focal lesions of supratentorial white matter in a 10-year-old boy affected by CCFDN. Other etiologies have been excluded and these lesions can be considered a new finding of the disease. We discuss a possible demyelinating mechanism affecting both peripheral and central myelin.

To evaluate the efficacy and tolerability of levetiracetam or oxcarbazepine as monotherapy in children with newly diagnosed benign epilepsy with centrotemporal spikes (BECTS). Twenty-one children (11 males, 10 females), aged between 5 and 13 years (mean 10.5 years), and 18 (10 M, 8 F), aged between 3.3 and 14 years (mean 8.4 years), were randomised to receive monotherapy with levetiracetam or oxcarbazepine, respectively. LEV was titrated up to 20-30 mg/kg/once or twice a day, and OXC up to 20-35 mg/kg once or twice a day. Thirty-nine consecutive children (21 males, 18 females), aged between 3.3 and 14 years (mean 10.7 years), were recruited into the study. Twenty-one were randomised on LEV (11 male, 10 female; mean age 10.5 years), and 18 on OXC (10 male, 8 female; mean age 8.4 years). After a mean follow-up period of 18.5 months (range 12-24 months), 19 out of 21 patients (90.5%) on levetiracetam, and 13 out of 18 (72,22%) on oxcarbazepine did not have further seizures. Mean serum level of LEV was 4.1 microg/ml (range 1.3-9.0), and of OXC was 15.2 microg/ml (range 4.2-27.5). Adverse side effects on LEV were reported in 3 children (14.3%), represented by mild and transient decreased appetite (2) and cephalalgia (1). They were reported on OXC in 2/18 (11.1%), including headache (1), and sedation (1). These preliminary data from an open, parallel group study suggest that levetiracetam and oxcarbazepine may be potentially effective and well tolerated drugs for children with BECTS who require treatment.

Levetiracetam is a new antiepileptic drug reported to be effective and well-tolerated in adults and children affected by epilepsy. Its lack of hepatic cytochrome metabolism is the theoretic basis for the absence of interactions with other drugs that follow this pathway. We present a 14-year-old girl who underwent orthotopic heart transplantation, followed by antirejection therapy including cyclosporine. Symptomatic occipital lobe epilepsy developed that was successfully treated with oxcarbazepine, but cyclosporine plasma levels decreased to below the antirejection threshold. Oxcarbazepine was replaced by levetiracetam. Levetiracetam did not affect the metabolism of cyclosporine, and cyclosporine plasma levels have remained in the therapeutic range up to now. The patient is still seizure-free and does not complain of any side effects after a 1-year follow-up. Further studies are necessary to confirm the lack of interactions between these drugs, which would make levetiracetam a useful therapeutic option in managing seizure control during antirejection therapy with cyclosporine.

Alexander disease is a rare, sporadic leukoencephalopathy characterized by white-matter abnormalities with frontal predominance and, as a rule, clinically associated with megalencephaly, seizures, spasticity, and psychomotor deterioration. We describe a boy who was diagnosed as affected by anorexia nervosa because of his refusal to eat, progressive weight loss, and psychologic disturbances. The observation of a hyperintense lesion on T2-weighed magnetic resonance images (MRIs) was initially explained as a pontine and extrapontine myelinolysis related to malnutrition. Following MRI and DNA analysis, we diagnosed a juvenile type of Alexander disease. Therefore, we can affirm the importance of the history and clinical examination to look for brainstem dysfunction in patients presenting with atypical anorexia nervosa.

FHL1 is a member of the four-and-a half-LIM (FHL) domain protein family and it is highly expressed in adult human skeletal muscle. It is believed to participate in sarcomere assembly, muscle growth and differentiation, and in the biomechanical stress responses. Mutations in FHL1 gene have been associated with different myopathies, including reducing body myopathy, scapuloperoneal (SP) 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 have generated a knock-in mouse model harboring the c.365 G > C Fhl1 mutation and have investigated the effects of this mutation at pre-symptomatic, phenotypic-onset, and late-stage of the disease, in hemizygous males and heterozygous females mice. Survival was comparable in mutant and wild-type animals. Adult hemizygous males mice showed a slowly progressive phenotype similar to human patients with relatively late-onset muscle weakness. In particular, we observed reduced forelimb strength and exercise capacity. Western blot analysis showed absence of FHL1 protein in muscle of hemizygous males at advanced stages. This animal model may help to elucidate the role of FHL1 in skeletal muscle and the pathomechanism of FHL1 mutations in X-linked dominant scapuloperoneal myopathy.

Autosomal recessive TK2 mutations have been associated with severe depletion of mitochondrial DNA (mtDNA) and devastating neuromuscular diseases in infants and children, and with mtDNA multiple deletions and progressive external ophthalmoplegia in adults. Similar to other mitochondrial disorders, only supportive treatments are available for TK2 deficiency. We generated a Tk2 H126N knock-in mouse model that manifests a phenotype strikingly similar to the human infantile encephalomyopathy. We demonstrated that lack of Tk2 activity cause nucleotide pools unbalance with severe reductions of deoxypyrimidine triphosphates (dTTP and dCTP) in brain and liver, leading to reduction of mtDNA copy number. To bypass Tk2 deficiency, we administered deoxypyrimidine monophosphates (dCMP + dTMP) to Tk2 knock-in mice by oral gavage from postnatal day 4, when mutant mice are biochemically affected but phenotypically normal. Assessment of 13-day old Tk2−/− mice treated with dCMP + dTMP 200 mg/kg/day each demonstrated that in mutant animals, the compounds: raise dCMP + dTMP concentrations; increase levels of mtDNA, augment quantity and activities of mitochondrial respiratory chain enzyme; and significantly prolong their lifespan (34 days with treatment vs 13 days untreated). A second trial of dCMP + dTMP at 400 mg/kg/day showed even greater phenotypic and biochemical improvements. No adverse effects were observed with both doses of dCMP + dTMP. Oral dCMP + dTMP supplementation is the first effective and safe treatment for TK2 deficiency in mice. This treatment can potentially be applied to patients.

IMPORTANCE: Mendelian forms of complex I deficiency are usually associated with fatal infantile encephalomyopathy. Application of "MitoExome" sequencing (deep sequencing of the entire mitochondrial genome and the coding exons of >1000 nuclear genes encoding the mitochondrial proteome) allowed us to reveal an unusual clinical variant of complex I deficiency due to a novel homozygous mutation in ACAD9. The patient had an infantile-onset but slowly progressive encephalomyopathy and responded favorably to riboflavin therapy. OBSERVATION: A 13-year-old boy had exercise intolerance, weakness, and mild psychomotor delay. Muscle histochemistry showed mitochondrial proliferation, and biochemical analysis revealed severe complex I deficiency (15% of normal). The level of complex I holoprotein was reduced as determined by use of Western blot both in muscle (54%) and in fibroblasts (57%). CONCLUSIONS AND RELEVANCE: The clinical presentation of complex I deficiency due ACAD9 mutations spans from fatal infantile encephalocardiomyopathy to mild encephalomyopathy. Our data support the notion that ACAD9 functions as a complex I assembly protein. ACAD9 is a flavin adenine dinucleotide-containing flavoprotein, and treatment with riboflavin is advisable.