COQ7 defect causes prenatal onset of mitochondrial CoQ10 deficiency with cardiomyopathy and gastrointestinal obstruction

COQ7 pathogenetic variants cause primary CoQ10 deficiency and a clinical phenotype of encephalopathy, peripheral neuropathy, or multisystemic disorder. Early diagnosis is essential for promptly starting CoQ10 supplementation. Here, we report novel compound heterozygous variants in the COQ7 gene responsible for a prenatal onset (20 weeks of gestation) of hypertrophic cardiomyopathy and intestinal dysmotility in a Bangladesh consanguineous family with two affected siblings. The main clinical findings were dysmorphisms, recurrent intestinal occlusions that required ileostomy, left ventricular non-compaction cardiomyopathy, ascending aorta dilation, arterial hypertension, renal dysfunction, diffuse skin desquamation, axial hypotonia, neurodevelopmental delay, and growth retardation. Exome sequencing revealed compound heterozygous rare variants in the COQ7 gene, c.613_617delGCCGGinsCAT (p.Ala205HisfsTer48) and c.403A>G (p.Met135Val). In silico analysis and functional in vitro studies confirmed the pathogenicity of the variants responsible for abolished activities of complexes I + III and II + III in muscle homogenate, severe decrease of CoQ10 levels, and reduced basal and maximal respiration in patients' fibroblasts. The first proband deceased at 14 months of age, whereas supplementation with a high dose of CoQ10 (30 mg/kg/day) since the first days of life modified the clinical course in the second child, showing a recovery of milestones acquirement at the last follow-up (18 months of age). Our study expands the clinical spectrum of primary CoQ10 deficiency due to COQ7 gene defects and highlights the essential role of multidisciplinary and combined approaches for a timely diagnosis.

Mitochondrial metabolism in neural stem cells and implications for neurodevelopmental and neurodegenerative diseases

Mitochondria are cytoplasmic organelles having a fundamental role in the regulation of neural stem cell (NSC) fate during neural development and maintenance.During embryonic and adult neurogenesis, NSCs undergo a metabolic switch from glycolytic to oxidative phosphorylation with a rise in mitochondrial DNA (mtDNA) content, changes in mitochondria shape and size, and a physiological augmentation of mitochondrial reactive oxygen species which together drive NSCs to proliferate and differentiate. Genetic and epigenetic modifications of proteins involved in cellular differentiation (Mechanistic Target of Rapamycin), proliferation (Wingless-type), and hypoxia (Mitogen-activated protein kinase)-and all connected by the common key regulatory factor Hypoxia Inducible Factor-1A-are deemed to be responsible for the metabolic shift and, consequently, NSC fate in physiological and pathological conditions.Both primary mitochondrial dysfunction due to mutations in nuclear DNA or mtDNA or secondary mitochondrial dysfunction in oxidative phosphorylation (OXPHOS) metabolism, mitochondrial dynamics, and organelle interplay pathways can contribute to the development of neurodevelopmental or progressive neurodegenerative disorders.This review analyses the physiology and pathology of neural development starting from the available in vitro and in vivo models and highlights the current knowledge concerning key mitochondrial pathways involved in this process.

Expanding the Clinical Spectrum of UBTF-Related Neurodevelopmental Disorder

Objectives

UBTF1 gene encodes for Upstream Binding Transcription Factor, an essential protein for RNA metabolism. A recurrent de novo variant (c.628G>A; p.Glu210Lys) has recently been associated with a childhood-onset neurodegenerative disorder characterized by motor and language regression, ataxia, dystonia, and acquired microcephaly. In this study, we report the clinical, metabolic, molecular genetics and neuroimaging findings and histologic, histochemical, and electron microscopy studies in muscle samples of 2 patients from unrelated families with a neurodevelopmental disorder.

Methods

Data were retrospectively analyzed by medical charts revision.

Results

Patient 1, a 16-year-old boy, presented a childhood-onset slowly progressive neurodegenerative disorder mainly affecting language skills, behavior, and motor coordination. Patient 2, a 22-year-old woman, presented with a severe and rapidly progressive disease with dystonic tetra paresis, acquired microcephaly, and severe cognitive deficit complicated by pseudobulbar syndrome characterized by involuntary and uncontrollable outbursts of laughing, dysphagia requiring tube feeding, and nocturnal hypoventilation treated with noninvasive ventilation. Both patients carried the recurrent previously described UBTF1 de novo variant and had signs of mitochondrial dysfunction at muscle biopsy. The metabolic profile of patient 2 also revealed a decrease in CSF biopterin.

Discussion

These case reports add new insights to the UBTF1 disease spectrum instrumental to improving the diagnostic rate in neurodevelopmental disorders.

From the Structural and (Dys)Function of ATP Synthase to Deficiency in Age-Related Diseases

The ATP synthase is a mitochondrial inner membrane complex whose function is essential for cell bioenergy, being responsible for the conversion of ADP into ATP and playing a role in mitochondrial cristae morphology organization. The enzyme is composed of 18 protein subunits, 16 nuclear DNA (nDNA) encoded and two mitochondrial DNA (mtDNA) encoded, organized in two domains, F_O and F₁. Pathogenetic variants in genes encoding structural subunits or assembly factors are responsible for fatal human diseases. Emerging evidence also underlines the role of ATP-synthase in neurodegenerative diseases as Parkinson’s, Alzheimer’s, and motor neuron diseases such as Amyotrophic Lateral Sclerosis. Post-translational modification, epigenetic modulation of ATP gene expression and protein level, and the mechanism of mitochondrial transition pore have been deemed responsible for neuronal cell death in vivo and in vitro models for neurodegenerative diseases. In this review, we will explore ATP synthase assembly and function in physiological and pathological conditions by referring to the recent cryo-EM studies and by exploring human disease models.

A late-stage assembly checkpoint of the human mitochondrial ribosome large subunit

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 Å) 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.

Rebelo-Guiomar et al. unveil late stage assembly intermediates of the human mitochondrial ribosome by inactivating the methyltransferase MRM2 in cells. Absence of MRM2 impairs organismal homeostasis, while its catalytic activity is dispensable for mitoribosomal biogenesis.

The Transcriptome of SH-SY5Y at Single-Cell Resolution: A CITE-Seq Data Analysis Workflow

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.

Evidence of enteric angiopathy and neuromuscular hypoxia in patients with mitochondrial neurogastrointestinal encephalomyopathy

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/mm² 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.

SARS-CoV-2 infection in patients with primary mitochondrial diseases: Features and outcomes in Italy

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.

Novel compound heterozygous pathogenic variants in nucleotide-binding protein like protein (NUBPL) cause leukoencephalopathy with multi-systemic involvement

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.

NSUN2 introduces 5-methylcytosines in mammalian mitochondrial tRNAs

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.

Deoxynucleoside Therapy for Thymidine Kinase 2-Deficient Myopathy

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.

Heterozygous SSBP1 start loss mutation co-segregates with hearing loss and the m.1555A>G mtDNA variant in a large multigenerational family

The m.1555A>G mtDNA variant causes maternally inherited deafness, but the reasons for the highly variable clinical penetrance are not known. Exome sequencing identified a heterozygous start loss mutation in SSBP1, encoding the single stranded binding protein 1 (SSBP1), segregating with hearing loss in a multi-generational family transmitting m.1555A>G, associated with mtDNA depletion and multiple deletions in skeletal muscle. The SSBP1 mutation reduced steady state SSBP1 levels leading to a perturbation of mtDNA metabolism, likely compounding the intra-mitochondrial translation defect due to m.1555A>G in a tissue-specific manner. This family demonstrates the importance of rare trans-acting genetic nuclear modifiers in the clinical expression of mtDNA disease.

Mitochondrial Neurogastrointestinal Encephalomyopathy: Into the Fourth Decade, What We Have Learned So Far

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an ultra-rare metabolic autosomal recessive disease, caused by mutations in the nuclear gene TYMP which encodes the enzyme thymidine phosphorylase. The resulting enzyme deficiency leads to a systemic accumulation of the deoxyribonucleosides thymidine and deoxyuridine, and ultimately mitochondrial failure due to a progressive acquisition of secondary mitochondrial DNA (mtDNA) mutations and mtDNA depletion. Clinically, MNGIE is characterized by gastrointestinal and neurological manifestations, including cachexia, gastrointestinal dysmotility, peripheral neuropathy, leukoencephalopathy, ophthalmoplegia and ptosis. The disease is progressively degenerative and leads to death at an average age of 37.6 years. As with the vast majority of rare diseases, patients with MNGIE face a number of unmet needs related to diagnostic delays, a lack of approved therapies, and non-specific clinical management. We provide here a comprehensive collation of the available knowledge of MNGIE since the disease was first described 42 years ago. This review includes symptomatology, diagnostic procedures and hurdles, in vitro and in vivo disease models that have enhanced our understanding of the disease pathology, and finally experimental therapeutic approaches under development. The ultimate aim of this review is to increase clinical awareness of MNGIE, thereby reducing diagnostic delay and improving patient access to putative treatments under investigation.

FGF21 underlies a hormetic response to metabolic stress in methylmalonic acidemia

Methylmalonic acidemia (MMA), an organic acidemia characterized by metabolic instability and multiorgan complications, is most frequently caused by mutations in methylmalonyl-CoA mutase (MUT). To define the metabolic adaptations in MMA in acute and chronic settings, we studied a mouse model generated by transgenic expression of Mut in the muscle. Mut-/-;TgINS-MCK-Mut mice accurately replicate the hepatorenal mitochondriopathy and growth failure seen in severely affected patients and were used to characterize the response to fasting. The hepatic transcriptome in MMA mice was characterized by the chronic activation of stress-related pathways and an aberrant fasting response when compared with controls. A key metabolic regulator, Fgf21, emerged as a significantly dysregulated transcript in mice and was subsequently studied in a large patient cohort. The concentration of plasma FGF21 in MMA patients correlated with disease subtype, growth indices, and markers of mitochondrial dysfunction but was not affected by renal disease. Restoration of liver Mut activity, by transgenesis and liver-directed gene therapy in mice or liver transplantation in patients, drastically reduced plasma FGF21 and was associated with improved outcomes. Our studies identify mitocellular hormesis as a hepatic adaptation to metabolic stress in MMA and define FGF21 as a highly predictive disease biomarker.

Retrospective natural history of thymidine kinase 2 deficiency

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.

Defective mitochondrial rRNA methyltransferase MRM2 causes MELAS-like clinical syndrome

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 encephalomyopathy 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 encephalopathy, lactic acidosis and stroke-like episodes (MELAS) syndrome, however, the common m.3243 A > G mutation was excluded. 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 human 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 completely 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.

Biallelic C1QBP Mutations Cause Severe Neonatal-, Childhood-, or Later-Onset Cardiomyopathy Associated with Combined Respiratory-Chain Deficiencies

Complement component 1 Q subcomponent-binding protein (C1QBP; also known as p32) is a multi-compartmental protein whose precise function remains unknown. It is an evolutionary conserved multifunctional protein localized primarily in the mitochondrial matrix and has roles in inflammation and infection processes, mitochondrial ribosome biogenesis, and regulation of apoptosis and nuclear transcription. It has an N-terminal mitochondrial targeting peptide that is proteolytically processed after import into the mitochondrial matrix, where it forms a homotrimeric complex organized in a doughnut-shaped structure. Although C1QBP has been reported to exert pleiotropic effects on many cellular processes, we report here four individuals from unrelated families where biallelic mutations in C1QBP cause a defect in mitochondrial energy metabolism. Infants presented with cardiomyopathy accompanied by multisystemic involvement (liver, kidney, and brain), and children and adults presented with myopathy and progressive external ophthalmoplegia. Multiple mitochondrial respiratory-chain defects, associated with the accumulation of multiple deletions of mitochondrial DNA in the later-onset myopathic cases, were identified in all affected individuals. Steady-state C1QBP levels were decreased in all individuals' samples, leading to combined respiratory-chain enzyme deficiency of complexes I, III, and IV. C1qbp-/- mouse embryonic fibroblasts (MEFs) resembled the human disease phenotype by showing multiple defects in oxidative phosphorylation (OXPHOS). Complementation with wild-type, but not mutagenized, C1qbp restored OXPHOS protein levels and mitochondrial enzyme activities in C1qbp-/- MEFs. C1QBP deficiency represents an important mitochondrial disorder associated with a clinical spectrum ranging from infantile lactic acidosis to childhood (cardio)myopathy and late-onset progressive external ophthalmoplegia.

Deoxycytidine and Deoxythymidine Treatment for Thymidine Kinase 2 Deficiency

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.

A Novel SUCLA2 Mutation Presenting as a Complex Childhood Movement 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.

Recurrent De Novo and Biallelic Variation of ATAD3A, Encoding a Mitochondrial Membrane Protein, Results in Distinct Neurological Syndromes

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 bor^R534W, 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 bor^WT 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.

Deoxypyrimidine monophosphate bypass therapy for thymidine kinase 2 deficiency

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.

Fhl1 W122S causes loss of protein function and late-onset mild myopathy

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.

TMEM14C is required for erythroid mitochondrial heme metabolism

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.

Deoxynucleoside stress exacerbates the phenotype of a mouse model of mitochondrial neurogastrointestinal encephalopathy

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.

Requirement of enhanced Survival Motoneuron protein imposed during neuromuscular junction maturation

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.

Mitochondrial encephalomyopathy due to a novel mutation in ACAD9

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.

Macrocytic anemia and mitochondriopathy resulting from a defect in sideroflexin 4

We used exome sequencing to identify mutations in sideroflexin 4 (SFXN4) in two children with mitochondrial disease (the more severe case also presented with macrocytic anemia). SFXN4 is an uncharacterized mitochondrial protein that localizes to the mitochondrial inner membrane. sfxn4 knockdown in zebrafish recapitulated the mitochondrial respiratory defect observed in both individuals and the macrocytic anemia with megaloblastic features of the more severe case. In vitro and in vivo complementation studies with fibroblasts from the affected individuals and zebrafish demonstrated the requirement of SFXN4 for mitochondrial respiratory homeostasis and erythropoiesis. Our findings establish mutations in SFXN4 as a cause of mitochondriopathy and macrocytic anemia.

MPV17 Mutations Causing Adult-Onset Multisystemic Disorder With Multiple Mitochondrial DNA Deletions

OBJECTIVE To identify the cause of an adult-onset multisystemic disease with multiple deletions of mitochondrial DNA (mtDNA). DESIGN Case report. SETTING University hospitals. PATIENT A 65-year-old man with axonal sensorimotor peripheral neuropathy, ptosis, ophthalmoparesis, diabetes mellitus, exercise intolerance, steatohepatopathy, depression, parkinsonism, and gastrointestinal dysmotility. RESULTS Skeletal muscle biopsy revealed ragged-red and cytochrome- c oxidase-deficient fibers, and Southern blot analysis showed multiple mtDNA deletions. No deletions were detected in fibroblasts, and the results of quantitative polymerase chain reaction showed that the amount of mtDNA was normal in both muscle and fibroblasts. Exome sequencing using a mitochondrial library revealed compound heterozygous MPV17 mutations (p.LysMet88-89MetLeu and p.Leu143*), a novel cause of mtDNA multiple deletions. CONCLUSIONS In addition to causing juvenile-onset disorders with mtDNA depletion, MPV17 mutations can cause adult-onset multisystemic disease with multiple mtDNA deletions.

Tissue-specific oxidative stress and loss of mitochondria in CoQ-deficient Pdss2 mutant mice

Primary human CoQ(10) deficiencies are clinically heterogeneous diseases caused by mutations in PDSS2 and other genes required for CoQ(10) biosynthesis. Our in vitro studies of PDSS2 mutant fibroblasts, with <20% CoQ(10) of control cells, revealed reduced activity of CoQ(10)-dependent complex II+III and ATP synthesis, without amplification of reactive oxygen species (ROS), markers of oxidative damage, or antioxidant defenses. In contrast, COQ2 and ADCK3 mutant fibroblasts, with 30-50% CoQ(10) of controls, showed milder bioenergetic defects but significantly increased ROS and oxidation of lipids and proteins. We hypothesized that absence of oxidative stress markers and cell death in PDSS2 mutant fibroblasts were due to the extreme severity of CoQ(10) deficiency. Here, we have investigated in vivo effects of Pdss2 deficiency in affected and unaffected organs of CBA/Pdss2(kd/kd) mice at presymptomatic, phenotypic-onset, and end-stages of the disease. Although Pdss2 mutant mice manifest widespread CoQ(9) deficiency and mitochondrial respiratory chain abnormalities, only affected organs show increased ROS production, oxidative stress, mitochondrial DNA depletion, and reduced citrate synthase activity, an index of mitochondrial mass. Our data indicate that kidney-specific loss of mitochondria triggered by oxidative stress may be the cause of renal failure in Pdss2(kd/kd) mice.

Next-generation sequencing reveals DGUOK mutations in adult patients with mitochondrial DNA multiple deletions

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.

Molecular diagnosis of infantile mitochondrial disease with targeted next-generation sequencing

Advances in next-generation sequencing (NGS) promise to facilitate diagnosis of inherited disorders. Although in research settings NGS has pinpointed causal alleles using segregation in large families, the key challenge for clinical diagnosis is application to single individuals. To explore its diagnostic use, we performed targeted NGS in 42 unrelated infants with clinical and biochemical evidence of mitochondrial oxidative phosphorylation disease. These devastating mitochondrial disorders are characterized by phenotypic and genetic heterogeneity, with more than 100 causal genes identified to date. We performed "MitoExome" sequencing of the mitochondrial DNA (mtDNA) and exons of ~1000 nuclear genes encoding mitochondrial proteins and prioritized rare mutations predicted to disrupt function. Because patients and healthy control individuals harbored a comparable number of such heterozygous alleles, we could not prioritize dominant-acting genes. However, patients showed a fivefold enrichment of genes with two such mutations that could underlie recessive disease. In total, 23 of 42 (55%) patients harbored such recessive genes or pathogenic mtDNA variants. Firm diagnoses were enabled in 10 patients (24%) who had mutations in genes previously linked to disease. Thirteen patients (31%) had mutations in nuclear genes not previously linked to disease. The pathogenicity of two such genes, NDUFB3 and AGK, was supported by complementation studies and evidence from multiple patients, respectively. The results underscore the potential and challenges of deploying NGS in clinical settings.

CoQ(10) deficiencies and MNGIE: two treatable mitochondrial disorders

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.

Fever as a seizure precipitant factor in Panayiotopoulos syndrome: a clinical and genetic study

PURPOSE

To examine fever as a precipitating factor for focal seizures in patients with Panayiotopoulos syndrome (PS) and evaluate the role of SCN1A in PS patients with seizures triggered by fever.

METHODS

From January 2000 to June 2008, we identified patients referred for seizures who fulfilled the criteria of PS. Patients were divided into two groups, according to the presence (group A) or the absence (group B) of seizures triggered by fever. Electroclinical features of the two groups were compared. In addition, an analysis of SCN1A in patients of group A was performed.

RESULTS

Thirty patients fulfilled the inclusion criteria. Eleven patients (36%) had at least one focal autonomic seizure triggered by fever (group A). In group A, 7/11 patients (63.5%) had the first focal autonomic seizure during a febrile illness. Two of these 7 patients were misdiagnosed at the onset of PS. The median age at the onset of PS was slightly lower in group A than in group B (p=.050). Moreover, patients in group A more frequently had a positive familial history of febrile seizures (FS) (p=.047). No mutations of SCN1A were found in any of the 10 patients screened.

CONCLUSION

Fever is a common trigger for focal autonomic seizures in PS. Knowing that an autonomic manifestation during fever can be an epileptic seizure could facilitate diagnosis and prevent unnecessary investigations and erroneous treatments. Moreover, our data show that SCN1A gene does not contribute significantly to susceptibility to autonomic seizures during fever in patients with PS.

FA2H-related disorders: a novel c.270+3A>T splice-site mutation leads to a complex neurodegenerative phenotype

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.

Clinical and genetic spectrum of mitochondrial neurogastrointestinal encephalomyopathy

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 (<10% of normal activity), we reviewed their medical records and laboratory studies. We identified 102 patients (50 females) with mitochondrial neurogastrointestinal encephalomyopathy and an average age of 32.4 years (range 11-59 years). We found 20 novel TYMP mutations. The average age-at-onset was 17.9 years (range 5 months to 35 years); however, the majority of patients reported the first symptoms before the age of 12 years. The patient distribution suggests a relatively high prevalence in Europeans, while the mutation distribution suggests founder effects for a few mutations, such as c.866A>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.

Metabolic disorders of fetal life: glycogenoses and mitochondrial defects of the mitochondrial respiratory chain

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.

Historical perspective on mitochondrial medicine

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.

Metabolic myopathies

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 Q(10) deficiencies, which are often treatable.

Intracerebral large artery disease in Aicardi-Goutières syndrome implicates SAMHD1 in vascular homeostasis

AIM

To describe a spectrum of intracerebral large artery disease in Aicardi-Goutières 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.

Progressive cerebral white matter involvement in a patient with Congenital Cataracts Facial Dysmorphisms Neuropathy (CCFDN)

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.

SAFA: A new measure to evaluate psychiatric symptoms detected in a sample of children and adolescents affected by eating disorders. Correlations with risk factors

In order to evaluate the psychiatric symptoms associated with a diagnosis of eating disorders (ED) we have administered a new psychometric instument: the Self Administrated Psychiatric Scales for Children and Adolescents (SAFA) test. SAFA was administered to a cohort of 97 patients, aged from 8.8 to 18, with an ED diagnosis. Age, body mass index (BMI) and BMI standard deviation score were analyzed. Furthermore, while looking for linkable risk factors, we evaluated other data that took an influence over the SAFA profile, like parental separation and family components' number. Compared to the range of statistical normality (based on Italian population), patients with bulimia nervosa or binge-eating disorder showed higher and pathologic values in specific subscales. When analyzing sex, males showed more pathologic values in most anxiety-related, obsessiveness-compulsiveness-related and insecurity subscales. A correlation among age, BMI and specific subscales (low self esteem, psychological aspects) emerged in participants with anorexia nervosa. In order to plan more appropriate diagnostic and therapeutic approaches in children or adolescents suffering from ED, the SAFA test can be an important instrument to evaluate psychiatric symptoms. Therefore, we propose to include this useful, simple self-administered test as a new screening tool for ED diagnosis.

Topiramate: effects on serum lipids and lipoproteins levels in children

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.

Levetiracetam or oxcarbazepine as monotherapy in newly diagnosed benign epilepsy of childhood with centrotemporal spikes (BECTS): an open-label, parallel group trial

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.