Phosphorylation Deficiency Research Articles

Novel heterozygous compound TRMT5 mutations associated with combined oxidative phosphorylation deficiency 26 in a Chinese family: a case report

BackgroundCombined oxidative phosphorylation deficiency 26 (COXPD26) is an autosomal recessive disorder characterized by early onset, developmental delay, gastrointestinal dysfunction, shortness of breath, exercise intolerance, hypotonia and muscle weakness, neuropathy, and spastic diplegia. This disease is considered to be caused by compound heterozygous mutations in the TRMT5 gene.Case presentationIn this study, we report a female child with COXPD26 manifesting as shortness of breath, gastrointestinal dysmotility, severe developmental delay, muscle hypotonia and weakness, exercise intolerance, renal and hepatic defects, and recurrent seizures with spastic diplegia. Interestingly, the hepatic feature was first observed in a COXPD26 patient. Medical exome sequencing with high coverage depth was employed to identify potential genetic variants in the patient. Novel compound heterozygous mutations of the TRMT5 gene were detected, which were c.881A>C (p.E294A) from her mother and c.1218G>C (p.Q406H) and c.1481C>T (p.T494M) from her father.ConclusionThe newly emerged clinical features and mutations of this patient provide useful information for further exploration of genotype–phenotype correlations in COXPD26.

FDX2 and ISCU Gene Variations Lead to Rhabdomyolysis With Distinct Severity and Iron Regulation.

Background and ObjectivesTo determine common clinical and biological traits in 2 individuals with variants in ISCU and FDX2, displaying severe and recurrent rhabdomyolyses and lactic acidosis.MethodsWe performed a clinical characterization of 2 distinct individuals with biallelic ISCU or FDX2 variants from 2 separate families and a biological characterization with muscle and cells from those patients.ResultsThe individual with FDX2 variants was clinically more affected than the individual with ISCU variants. Affected FDX2 individual fibroblasts and myoblasts showed reduced oxygen consumption rates and mitochondrial complex I and PDHc activities, associated with high levels of blood FGF21. ISCU individual fibroblasts showed no oxidative phosphorylation deficiency and moderate increase of blood FGF21 levels relative to controls. The severity of the FDX2 individual was not due to dysfunctional autophagy. Iron was excessively accumulated in ISCU-deficient skeletal muscle, which was accompanied by a downregulation of IRP1 and mitoferrin2 genes and an upregulation of frataxin (FXN) gene expression. This excessive iron accumulation was absent from FDX2 affected muscle and could not be correlated with variable gene expression in muscle cells.DiscussionWe conclude that FDX2 and ISCU variants result in a similar muscle phenotype, that differ in severity and skeletal muscle iron accumulation. ISCU and FDX2 are not involved in mitochondrial iron influx contrary to frataxin.

Hypoglycemia with lactic acidosis caused by a new MRPS2 gene mutation in a Chinese girl: a case report

BackgroundMitochondrial ribosomal protein S2 (MRPS2) gene mutation, which is related to severe hypoglycemia and lactic acidosis, is rarely reported globally.Case presentationWe report a case of a new MRPS2 gene mutation in a Chinese girl who presented with hypoglycemia and lactic acidosis. A homozygous C.412C > G variant that could cause complex oxidative phosphorylation deficiency and had not been reported before was identified. The clinical manifestations included recurrent vomiting, hypoglycemia, lactic acidosis, sensorineural hearing loss, and gall bladder calculi. Hypoglycemia and lactic acidosis improved after the administration of sugary liquid and supportive treatments.ConclusionsRecurrent hypoglycemia with lactic acidosis and sensorineural hearing loss should lead to suspicion of mitochondrial defects and the early refinement of genetic tests.

Chlorfenapyr Induce Oxidative Phosphorylation Deficiency in Exposed Rat and the Quinoa Effective Role

Chlorfenapyr Induce Oxidative Phosphorylation Deficiency in Exposed Rat and the Quinoa Effective Role

Складнощі діагностики рідкісної вродженої мітохондріальної патології — комбінованого дефіциту окисного фосфорилювання 26-го типу в дитини раннього віку: клінічний випадок

Hereditary mitochondrial diseases are a consequence of congenital errors in energy metabolism with very variable and predominantly multisystem manifestations, they require differential diagnosis with a wide range of phenotypically similar nosologies, and their verification is a complex problem with a need of a multidisciplinary approach. The article describes a rare clinical case diagnosed in a girl of early age of a congenital mitochondrial pathology with autosomal recessive inheritance — a combined oxidative phosphorylation deficiency of type 26 (COXPD-26) due to two mutations in the heterozygous state of the TRMT5 gene (tRNA methyltransferase 5) on the chromosome 14q23. The patient's illness was accompanied by a debut from birth and was characterized by insufficient weight gain, manifestations of cardiomyopathy, repeated intercurrent infectious diseases with increased activity of blood transaminases, creatine kinase-MB, hepatopathy with hypoalbuminemia, convulsive syndrome, intolerance to valproic acid, progressive delay in stato-kinetic and psychoverbal development, that is, the symptomatology was characterized by progression, multisystem character with predominant damage to the heart, liver and nervous system. The diagnostic algorithm for mitochondrial diseases is one of the most complex in medical practice. In young children, persistent or progressive multisystem disorder of unknown etiology, unknown multiple complex neurological manifestations or neurological monosymptom with involvement of other systems, less often — specific clinical symptoms; persistent lactic acidosis, other positive or questionable laboratory screening findings are suspicious of probable mitochondrial pathology. Numerous hospitalizations, repeated consultations by different specialists, multiple additional labtests, and multiple conflicting diagnoses may indicate a possible mitochondrial pathology. Only whole exome sequencing of a blood sample with an analysis of variations in the number of copies of genes and genomic sequencing of a new generation with targeted genetic testing made it possible to diagnose in a child a hereditary metabolic disorder from the group of defects in the mitochondrial respiratory chain — a combined deficiency of oxidative phosphorylation type 26, previously described in only a few patients. The research was carried out in accordance with the principles of the Helsinki declaration. The informed consent of the patient was obtained for conducting the studies. No conflict of interest was declared by the authors. Key words: mitochondrial pathology, combined deficiency of oxidative phosphorylation of type 26 (COXPD-26), clinical case.

Dysfunctional mitochondrial translation and combined oxidative phosphorylation deficiency in a mouse model of hepatoencephalopathy due to Gfm1 mutations.

Hepatoencephalopathy due to combined oxidative phosphorylation deficiency type 1 (COXPD1) is a recessive mitochondrial translation disorder caused by mutations in GFM1, a nuclear gene encoding mitochondrial elongation factor G1 (EFG1). Patients with COXPD1 typically present hepatoencephalopathy early after birth with rapid disease progression, and usually die within the first few weeks or years of life. We have generated two different mouse models: a Gfm1knock-in (KI) harboring the p.R671C missense mutation, found in at least 10 patients who survived more than 1year, and a Gfm1knock-out (KO) model. Homozygous KO mice (Gfm1-/- ) were embryonically lethal, whereas homozygous KI (Gfm1R671C/R671C ) mice were viable and showed normal growth. R671C mutation in Gfm1 caused drastic reductions in the mitochondrial EFG1 protein content in different organs. Six- to eight-week-old Gfm1R671C/R671C mice showed partial reductions of in organello mitochondrial translation and respiratory complex IV enzyme activity in the liver. Compound heterozygous Gfm1R671C/- showed a more pronounced decrease of EFG1 protein in liver and brain mitochondria, as compared with Gfm1R671C/R671C mice. At 8weeks of age, their mitochondrial translation rates were significantly reduced in both tissues. Additionally, Gfm1R671C/- mice showed combined oxidative phosphorylation deficiency (reduced complex I and IV enzyme activities in liver and brain), and blue native polyacrylamide gel electrophoresis analysis revealed lower amounts of both affected complexes. We conclude that the compound heterozygous Gfm1R671C/- mouse presents a clear dysfunctional molecular phenotype, showing impaired mitochondrial translation and combined respiratory chain dysfunction, making it a suitable animal model for the study of COXPD1.

Astrocytic Changes in Mitochondrial Oxidative Phosphorylation Protein Levels in Parkinson's Disease

Mitochondrial dysfunction within neurons, particularly those of the substantia nigra, has been well characterized in Parkinson's disease and is considered to be related to the pathogenesis of this disorder. Dysfunction within this important organelle has been suggested to impair neuronal communication and survival; however, the reliance of astrocytes on mitochondria and the impact of their dysfunction on this essential cell type are less well characterized. This study aimed to uncover whether astrocytes harbor oxidative phosphorylation (OXPHOS) deficiencies in Parkinson's disease and whether these deficiencies are more likely to occur in astrocytes closely associated with neurons or those more distant from them. Postmortem human brain sections from patients with Parkinson's disease were subjected to imaging mass cytometry for individual astrocyte analysis of key OXPHOS proteins across all five complexes. We show the variability in the astrocytic expression of mitochondrial proteins between individuals. In addition, we found that there is evidence of deficiencies in respiratory chain subunit expression within these important glia and changes, particularly in mitochondrial mass, associated with Parkinson's disease and that are not simply a consequence of advancing age. Our data show that astrocytes, like neurons, are susceptible to mitochondrial defects and that these could have an impact on their reactivity and ability to support neurons in Parkinson's disease.

Novel Mutations in the GTPBP3 Gene for Mitochondrial Disease and Characteristics of Related Phenotypic Spectrum: The First Three Cases From China.

Combined Oxidative Phosphorylation Deficiency 23 (COXPD23) caused by mutations in GTPBP3 gene is a rare mitochondrial disease, and this disorder identified from the Chinese population has not been described thus far. Here, we report a case series of three patients with COXPD23 caused by GTPBP3 mutations, from a severe to a mild phenotype. The main clinical features of these patients include lactic acidosis, myocardial damage, and neurologic symptoms. Whole genome sequencing and targeted panels of candidate human mitochondrial genome revealed that patient 1 was a compound heterozygote with novel mutations c.413C > T (p. A138V) and c.509_510del (p. E170Gfs∗42) in GTPBP3. Patient 2 was a compound heterozygote with novel mutations c.544G > T (p. G182X) and c.785A > C (p.Q262P), while patient 3 was a compound heterozygote with a previously reported mutation c.424G > A (p.E142K) and novel mutation c.785A > C (p.Q262P). In conclusion, we first describe three Chinese individuals with COXPD23, and discuss the genotype-phenotype correlations of GTPBP3 mutations. Our findings provide novel information in the diagnosis and genetic counseling of patients with mitochondrial disease.

Mechanisms of the effect of oxidative phosphorylation deficiencies on the skeletal muscle bioenergetic system in patients with mitochondrial myopathies.

Simulations carried out using a previously developed model of the skeletal muscle bioenergetic system, involving the "inorganic phosphate (Pi) double-threshold" mechanism of muscle fatigue, lead to the conclusion that a decrease in the oxidative phosphorylation (OXPHOS) activity, caused by mutations in mitochondrial or nuclear DNA, is the main mechanism underlying the changes in the kinetic properties of the system in mitochondrial myopathies (MM). These changes generally involve the very-heavy-exercise-like behavior and exercise termination because of fatigue at low work intensities. In particular, a sufficiently large (at a given work intensity) decrease in OXPHOS activity leads to slowing of the primary phase II of the oxygen uptake (V̇o2) on-kinetics, decrease in maximal V̇o2 (V̇o2max), appearance of the slow component of the V̇o2 on-kinetics, exercise intolerance, and lactic acidosis at relatively low power outputs encountered in experimental studies in patients with MM. Thus, the "Pi double-threshold" mechanism of muscle fatigue is able to account, at least semiquantitatively, for various kinetic effects of inborn OXPHOS deficiencies of the skeletal muscle bioenergetic system. Exercise can be potentially lengthened and V̇o2max elevated in patients with MM through an increase in peak Pi (Pipeak), at which exercise is terminated because of fatigue. Generally, a mechanism underlying the kinetic effects of OXPHOS deficiencies on the skeletal muscle bioenergetic system in MM is proposed that was absent in the literature.NEW & NOTEWORTHY A mechanism of the OXPHOS deficiencies-induced changes of the skeletal muscle bioenergetic system in patients with mitochondrial myopathies (MM), namely, appearance of the slow component of the V̇o2 on-kinetics at relatively low work intensities, slowed primary phase II of the V̇o2 on-kinetics, lowered V̇o2max, and lactic acidosis is proposed. It involves a decrease in OXPHOS activity acting through the "Pi double-threshold" mechanism of muscle fatigue comprising initiation of the additional ATP usage and termination of exercise.

COXPD9 in an individual from Puerto Rico and literature review

Defects of mitoribosome assembly with destabilization of mitochondrial ribosomal proteins and subsequent aberrant mitochondrial translation machinery are one of the emerging categories of human mitochondrial disease. Mitochondrial translation deficiency constitutes a growing cause of combined oxidative phosphorylation deficiency and overall causes a set of clinically heterogeneous multi-systemic diseases. We present here the sixth individual with combined oxidative phosphorylation deficiency-9 (COXPD9) secondary to a likely pathogenic homozygous MRPL3 variant c.571A > C; p.(Thr191Pro). MRPL3 encodes a large mitochondrial ribosome subunit protein, impairing the mitochondrial translation and resulting in multisystem disease. Similar to previously reported individuals, this reported female proband presented with psychomotor retardation, sensorineural hearing loss, hypertrophic cardiomyopathy, failure to thrive, and lactic acidosis. Further, she has additional, previously unreported, features including Leigh syndrome, cataracts, hypotonia, scoliosis, myopathy, exercise intolerance, childhood-onset cardiomyopathy, and microcephaly. This subject is the oldest reported individual with COXPD9. This report also summarizes the clinical and molecular data of the previously reported individuals with COXPD9 to describe the full phenotypic spectrum.

Generation of three human induced pluripotent stem cell lines, LUMCi024-A, LUMCi025-A, and LUMCi026-A, from two patients with combined oxidative phosphorylation deficiency 8 and a related control

Combined Oxidative Phosphorylation Deficiency 8 (COXPD8) is an autosomal recessive disorder causing lethal childhood-onset hypertrophic cardiomyopathy. Homozygous or compound heterozygous mutations in the nuclear-encoded mitochondrial alanyl-tRNA synthetase 2 (AARS2) gene underly the pathology. We generated induced pluripotent stem cells (hiPSCs) from two patients carrying the heterozygous compound c.1774 C>T, c.2188 G>A and c.2872 C>T AARS2 mutations, as well as a related healthy control carrying the c.2872 C>T AARS2 mutation. All hiPSC-lines expressed pluripotency markers, maintained a normal karyotype, and differentiated towards the three germ layer derivatives in vitro. These lines can be used to model COXPD8 or mitochondrial dysfunction.

Metabolic impact of pathogenic variants in the mitochondrial glutamyl‐tRNA synthetase EARS2

Glutamyl-tRNA synthetase 2 (encoded by EARS2) is a mitochondrial aminoacyl-tRNA synthetase required to translate the 13 subunits of the electron transport chain encoded by the mitochondrial DNA. Pathogenic EARS2 variants cause combined oxidative phosphorylation deficiency, subtype 12 (COXPD12), an autosomal recessive disorder involving lactic acidosis, intellectual disability, and other features of mitochondrial compromise. Patients with EARS2 deficiency present with variable phenotypes ranging from neonatal lethality to a mitigated disease with clinical improvement in early childhood. Here, we report a neonate homozygous for a rare pathogenic variant in EARS2 (c.949G>T; p.G317C). Metabolomics in primary fibroblasts from this patient revealed expected abnormalities in TCA cycle metabolites, as well as numerous changes in purine, pyrimidine, and fatty acid metabolism. To examine genotype-phenotype correlations in COXPD12, we compared the metabolic impact of reconstituting these fibroblasts with wild-type EARS2 versus four additional EARS2 variants from COXPD12 patients with varying clinical severity. Metabolomics identified a group of signature metabolites, mostly from the TCA cycle and amino acid metabolism, that discriminate between EARS2 variants causing relatively mild and severe COXPD12. Taken together, these findings indicate that metabolomics in patient-derived fibroblasts may help establish genotype-phenotype correlations in EARS2 deficiency and likely other mitochondrial disorders.

EP229 - A case of combined oxidative phosphorylation deficiency 5 with prenatal onset

eP229 - A case of combined oxidative phosphorylation deficiency 5 with prenatal onset

Obstetrical history of a family with combined oxidative phosphorylation deficiency 3 and methylenetetrahydrofolate reductase polymorphisms

Abstract Objectives Recurrent pregnancy loss (RPL) is a devastating complication of pregnancy with various etiologic backgrounds. Case presentation We present a case of combined oxidative phosphorylation deficiency 3 (COXPD3) carrier pregnant woman with Methylenetetrahydrofolate reductase (MTHFR) polymorphisms. She had five pregnancy losses and a postpartum death due to COXPD3. The patient was admitted to our clinic for the first time at her seventh pregnancy with oocyte donation. The patient was registered in a special antenatal care program and delivered a healthy baby at term. Her eighth pregnancy was terminated due to COXPD3 which was prenatally diagnosed. Conclusions Comprehensive and individualized approaches are necessary in RPL cases to obtain optimal outcomes.

Therapeutical Management and Drug Safety in Mitochondrial Diseases-Update 2020.

Mitochondrial diseases (MDs) are a group of genetic disorders that may manifest with vast clinical heterogeneity in childhood or adulthood. These diseases are characterized by dysfunctional mitochondria and oxidative phosphorylation deficiency. Patients are usually treated with supportive and symptomatic therapies due to the absence of a specific disease-modifying therapy. Management of patients with MDs is based on different therapeutical strategies, particularly the early treatment of organ-specific complications and the avoidance of catabolic stressors or toxic medication. In this review, we discuss the therapeutic management of MDs, supported by a revision of the literature, and provide an overview of the drugs that should be either avoided or carefully used both for the specific treatment of MDs and for the management of comorbidities these subjects may manifest. We finally discuss the latest therapies approved for the management of MDs and some ongoing clinical trials.

Dual function of GTPBP6 in biogenesis and recycling of human mitochondrial ribosomes.

Translation and ribosome biogenesis in mitochondria require auxiliary factors that ensure rapid and accurate synthesis of mitochondrial proteins. Defects in translation are associated with oxidative phosphorylation deficiency and cause severe human diseases, but the exact roles of mitochondrial translation-associated factors are not known. Here we identify the functions of GTPBP6, a homolog of the bacterial ribosome-recycling factor HflX, in human mitochondria. Similarly to HflX, GTPBP6 facilitates the dissociation of ribosomes in vitro and in vivo. In contrast to HflX, GTPBP6 is also required for the assembly of mitochondrial ribosomes. GTPBP6 ablation leads to accumulation of late assembly intermediate(s) of the large ribosomal subunit containing ribosome biogenesis factors MTERF4, NSUN4, MALSU1 and the GTPases GTPBP5, GTPBP7 and GTPBP10. Our data show that GTPBP6 has a dual function acting in ribosome recycling and biogenesis. These findings contribute to our understanding of large ribosomal subunit assembly as well as ribosome recycling pathway in mitochondria.

Early Onset of Combined Oxidative Phosphorylation Deficiency in Two Chinese Brothers Caused by a Homozygous (Leu275Phe) Mutation in the C1QBP Gene.

Mitochondrial diseases constitute a group of heterogeneous hereditary diseases caused by impairments in mitochondrial oxidative phosphorylation and abnormal cellular energy metabolism. C1QBP plays an important role in mitochondrial homeostasis. In this study, clinical, laboratory examinations, 12-lead electrocardiographic, ultrasonic cardiogram, and magnetic resonance imaging data were collected from four members of a Chinese family. Whole exome were amplified and sequenced for the proband. The structure of protein encoded by the mutation was predicted using multiple software programs. The proband was a 14-year old boy with myocardial hypertrophy, exercise intolerance, ptosis, and increased lactate. His 9-year old brother exhibited similar clinical manifestations while the phenomenon of ptosis was not as noticeable as the proband. The onset of this disease was in infancy in both cases. They were born after uneventful pregnancies of five generation blood relative Chinese parents. A homozygous mutation (Leu275Phe) in the C1QBP gene was identified in both brothers in an autosomal recessive inherited pattern. Their parents were heterozygous mutation carriers without clinical manifestations. We demonstrated that a homozygous C1QBP- P.Leu275Phe mutation in an autosomal recessive inherited mode of inheritance caused early onset combined oxidative phosphorylation deficiency 33 (COXPD 33) (OMIM:617713) in two brothers from a Chinese family.

Novel compound heterozygous TARS2 variants in a Chinese family with mitochondrial encephalomyopathy: a case report

BackgroundMitochondrial encephalomyopathy caused by bi-allelic deleterious variants in TARS2 is rare. To date, only two pedigrees were reported in the literature and the connection between the gene and disease needs further study.Case presentationWe report one infant who presented with limb hypertonia, epilepsy, developmental delay, and increased serum lactate from a non-consanguineous Chinese family. Whole-genome sequencing was performed to help to underlie the cause. We identified compound heterozygous variants c.470C > G, p.Thr157Arg and c.2143G > A, p.Glu715Lys in TARS2 and the variants were confirmed by Sanger sequencing. The patient was diagnosed with combined oxidative phosphorylation deficiency 21 according to the Online Mendelian Inheritance in Man (OMIM) database based on the clinical data and the deleterious effect of the two variants in TARS2 predicted by in silico tools.ConclusionsWe presented one case diagnosed with combined oxidative phosphorylation deficiency 21 based on clinical characteristics and genetic analysis. This is the first case in China and the fourth case in the world based on our document retrieval. This study facilitates the understanding of combined oxidative phosphorylation deficiency disease and demonstrates that the next-generation sequencing has a high potential to study inherited disease with high phenotypic heterogeneity and genetic heterogeneity including mitochondrial diseases such as combined oxidative phosphorylation deficiency.

Decoding mitochondrial heterogeneity in single muscle fibres by imaging mass cytometry

The study of skeletal muscle continues to support the accurate diagnosis of mitochondrial disease and remains important in delineating molecular disease mechanisms. The heterogeneous expression of oxidative phosphorylation proteins and resulting respiratory deficiency are both characteristic findings in mitochondrial disease, hence the rigorous assessment of these at a single cell level is incredibly powerful. Currently, the number of proteins that can be assessed in individual fibres from a single section by immunohistochemistry is limited but imaging mass cytometry (IMC) enables the quantification of further, discrete proteins in individual cells. We have developed a novel workflow and bespoke analysis for applying IMC in skeletal muscle biopsies from patients with genetically-characterised mitochondrial disease, investigating the distribution of nine mitochondrial proteins in thousands of single muscle fibres. Using a semi-automated analysis pipeline, we demonstrate the accurate quantification of protein levels using IMC, providing an accurate measure of oxidative phosphorylation deficiency for complexes I–V at the single cell level. We demonstrate signatures of oxidative phosphorylation deficiency for common mtDNA variants and nuclear-encoded complex I variants and a compensatory upregulation of unaffected oxidative phosphorylation components. This technique can now be universally applied to evaluate a wide range of skeletal muscle disorders and protein targets.

Generation of two induced pluripotent stem cell lines (XACHi0010-A, XACHi0011-A) from a Chinese family with combined oxidative phosphorylation deficiency carrying homozygous and heterozygous C1QBP-L275F mutation.

Induced pluripotent stem cell lines (iPSCs) were generated from peripheral blood mononuclear cells (PBMCs) isolated from the peripheral blood of a 14year-old boy and his mother using same protocols. Diagnosis of combined oxidative phosphorylation deficiency (COXPD) was established after identifying a homozygous c.823C>T(p.L275F) variant in C1QBP gene carried by the boy, inherited from his asymptomatic consanguineous parents carrying this heterozygous variant. PBMCs were reprogrammed using non-integrative sendai viral vectors containing reprogramming factors OCT4, SOX2, KLF4 and C-MYC. iPSCs were shown to express pluripotent markers, have trilineage differentiation potential, carry C1QBP-L275F mutation, have a normal karyotype. These lines are useful tools for studying the pathophysiological mechanism of COXPD.