Computational analysis of a novel mutation in ETFDH gene highlights its long-range effects on the FAD-binding motif

Case report: Novel ETFDH compound heterozygous mutations identified in a patient with late-onset glutaric aciduria type II

Glutaric aciduria type II (GA II) is an autosomal recessive metabolic disorder of fatty acid, amino acid, and choline metabolism. The late-onset form of this disorder is caused by a defect in the mitochondrial electron transfer flavoprotein dehydrogenase or the electron transfer flavoprotein dehydrogenase (ETFDH) gene. Thus far, the high clinical heterogeneity of late-onset GA II has brought a great challenge for its diagnosis. In this study, we reported a 21-year-old Chinese man with muscle weakness, vomiting, and severe pain. Muscle biopsy revealed myopathological patterns of lipid storage myopathy, and urine organic acid analyses showed a slight increase in glycolic acid. All the aforementioned results were consistent with GA II. Whole-exome sequencing (WES), followed by bioinformatics and structural analyses, revealed two compound heterozygous missense mutations: c.1034A > G (p.H345R) on exon 9 and c.1448C>A (p.P483Q) on exon 11, which were classified as "likely pathogenic" according to American College of Medical Genetics and Genomics (ACMG). In conclusion, this study described the phenotype and genotype of a patient with late-onset GA II. The two novel mutations in ETFDH were found in this case, which further expands the list of mutations found in patients with GA II. Because of the treatability of this disease, GA II should be considered in all patients with muscular symptoms and acute metabolism decompensation such as hypoglycemia and acidosis.

Clinical Presentations and Genetic Characteristics of Late-Onset MADD Due to ETFDH Mutations in Five Patients: A Case Series

Background: Late-onset multiple acyl-CoA dehydrogenase deficiency (LO-MADD) describes a curable autosomal recessive genetic disease caused by ETFDH mutations that result in defects in ETF-ubiquinone oxidoreductase. Almost all patients are responsive to riboflavin. This study describes the clinical presentations and genetic characteristics of five LO-MADD patients.

Methods: From 2018 to 2021, we collected clinical and genetic data on five patients diagnosed with LO-MADD at our hospital and retrospectively analyzed their clinical characteristics, laboratory examination, electromyography, muscle biopsy, genetic analysis, and outcome data.

Results: This study included three males and two females with mean onset age of 37.8 years. Fluctuating exercise intolerance was the most common presentation. Serum creatine kinase (CK) levels were significantly elevated in all patients, and plasma acylcarnitine profiles revealed an increase in long-chain acylcarnitine species in three cases. The urinary organic acid study revealed a high level of hydroxyglutaric acid in all patients. Electrophysiology demonstrated myogenic impairment. Muscle biopsies revealed lipid storage myopathy. Molecular analysis identified nine mutations (three novels and six reported) in ETFDH. Exercise intolerance and muscle weakness were dramatically improved in all patients treated with riboflavin (100 mg) daily following diagnosis.

Conclusions: LO-MADD is caused by ETFDH variants and responds well to riboflavin. Three novel ETFDH pathogenic variants were identified, expanding their spectrum in the Chinese population and facilitating future interpretation and analysis of ETFDH mutations.

Clinical, pathological and genetic features and follow-up of 110 patients with late-onset MADD: A single-center retrospective study

BACKGROUND

To observe a long-term prognosis in late-onset multiple acyl-coenzyme-A dehydrogenation deficiency(MADD) patients and to determine whether riboflavin should be administrated in the long-term and high-dosage manner.

METHODS

We studied the clinical, pathological and genetic features of 110 patients with late-onset MADD in a single neuromuscular center. The plasma riboflavin levels and a long-term follow-up were performed.

RESULTS

Fluctuating proximal muscle weakness, exercise intolerance and dramatic responsiveness to riboflavin treatment were essential clinical features for all 110 MADD patients. Among them, we identified 106 cases with ETFDH variants, 1 case with FLAD1 variants and 3 cases without causal variants. On muscle pathology, fibers with cracks, atypical ragged red fibers(aRRFs) and diffuse decrease of SDH activity were the distinctive features of these MADD patients. The plasma riboflavin levels before treatment were significantly decreased in these patients as compared to healthy controls. Among 48 MADD patients with a follow-up of 6.1 years on average, 31 patients were free of muscle weakness recurrence, while 17 patients had episodes of slight muscle weakness upon riboflavin withdrawal, but recovered after retaking a small-dose of riboflavin for a short-term. Multivariate Cox regression analysis showed vegetarian diet and masseter weakness were independent risk factors for muscle weakness recurrence.

CONCLUSION

Fibers with cracks, aRRFs and diffuse decreased SDH activity distinguish MADD from other genotypes of lipid storage myopathy. For late-onset MADD, increased fatty acid oxidation and reduced riboflavin levels can induce episodes of muscle symptoms, which can be treated by short-term and small-dose of riboflavin therapy.

Clinical, Biochemical, and Genetic Heterogeneity in Glutaric Aciduria Type II Patients

The variants of electron transfer flavoprotein (ETFA, ETFB) and ETF dehydrogenase (ETFDH) are the leading cause of glutaric aciduria type II (GA-II). In this study, we identified 13 patients harboring six variants of two genes associated with GA-II. Out of the six variants, four were missense, and two were frameshift mutations. A missense variant (ETFDH:p.Gln269His) was observed in a homozygous state in nine patients. Among nine patients, three had experienced metabolic crises with recurrent vomiting, abdominal pain, and nausea. In one patient with persistent metabolic acidosis, hypoglycemia, and a high anion gap, the ETFDH:p.Gly472Arg, and ETFB:p.Pro94Thrfs*8 variants were identified in a homozygous, and heterozygous state, respectively. A missense variant ETFDH:p.Ser442Leu was detected in a homozygous state in one patient with metabolic acidosis, hypoglycemia, hyperammonemia and liver dysfunction. The ETFDH:p.Arg41Leu, and ETFB:p.Ile346Phefs*19 variants were observed in a homozygous state in one patient each. Both these variants have not been reported so far. In silico approaches were used to evaluate the pathogenicity and structural changes linked with these six variants. Overall, the results indicate the importance of a newborn screening program and genetic investigations for patients with GA-II. Moreover, careful interpretation and correlation of variants of uncertain significance with clinical and biochemical findings are needed to confirm the pathogenicity of such variants.

Multiple Acyl-CoA Dehydrogenase Deficiency with Variable Presentation Due to a Homozygous Mutation in a Bedouin Tribe

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a fatty acid and amino acid oxidation defect caused by a deficiency of the electron-transfer flavoprotein (ETF) or the electron-transfer flavoprotein dehydrogenase (ETFDH). There are three phenotypes of the disease, two neonatal forms and one late-onset. Previous studies have suggested that there is a phenotype-genotype correlation. We report on six patients from a single Bedouin tribe, five of whom were sequenced and found to be homozygous to the same variant in the ETFDH gene, with variable severity and age of presentation. The variant, NM_004453.3 (ETFDH): c.524G>A, p.(R175H), was previously recognized as pathogenic, although it has not been reported in the literature in a homozygous state before. R175H is located near the FAD binding site, likely affecting the affinity of FAD for EFT:QO. The single homozygous ETFDH pathogenic variant was found to be causing MADD in this cohort with an unexpectedly variable severity of presentation. The difference in severity could partly be explained by early diagnosis via newborn screening and early treatment with the FAD precursor riboflavin, highlighting the importance of early detection by newborn screening.

ETF dehydrogenase advances in molecular genetics and impact on treatment

Electron transfer flavoprotein dehydrogenase, also called ETF-ubiquinone oxidoreductase (ETF-QO), is a protein localized in the inner membrane of mitochondria, playing a central role in the electron-transfer system. Indeed, ETF-QO mediates electron transport from flavoprotein dehydrogenases to the ubiquinone pool. ETF-QO mutations are often associated with riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency (RR-MADD, OMIM#231680), a multisystem genetic disease characterized by various clinical manifestations with different degrees of severity. In this review, we outline the clinical features correlated with ETF-QO deficiency and the benefits obtained from different treatments, such as riboflavin, L-carnitine and/or coenzyme Q10 supplementation, and a diet poor in fat and protein. Moreover, we provide a detailed summary of molecular and bioinformatic investigations, describing the mutations identified in ETFDH gene and highlighting their predicted impact on enzymatic structure and activity. In addition, we report biochemical and functional analysis, performed in HEK293 cells and patient fibroblasts and muscle cells, to show the relationship between the nature of ETFDH mutations, the variable impairment of enzyme function, and the different degrees of RR-MADD severity. Finally, we describe in detail 5 RR-MADD patients carrying different ETFDH mutations and presenting variable degrees of clinical symptom severity.

Investigation of Cyc1 protein structure stability after H53I mutation using computational approaches to improve redox potential

Acidithiobacillus ferrooxidans (Af) is an acidophilic bacterium that grows in rigid surroundings and gets its own energy from the oxidation of Fe²⁺ to Fe³⁺. These bacteria are involved in the bioleaching process. Cyc₁ is a periplasmic protein with a crucial role in electron transportation in the respiratory chain. His53 of the Cyc₁ protein, involved in electron transfer to CoxB, was selected for mutation and bioinformatics studies. His53 was substituted by Ile using PyMol software. Molecular dynamics simulations were performed for wild and mutant types of Cyc₁ protein. The conformational changes of mutated protein were studied by analyzing RMSD, RMSF, SASA, Rg, H Bond, and DSSP. The results of the RMSF analysis indicated an increase in the flexibility of the ligand in the mutant. Finally, active site instability leads to an increase in the value of E₀ at the mutation point and improving electron transfer. On the other, His53 in Cyc₁ is interconnected to Glu126 in CoxB through the water molecule (W76) and hydrogen bonding. In the H53I mutation, there was a decrease in the distance between H2O 2030, 2033, and isoleucine 53, and subsequently, the distance to the water molecule 76 between the two proteins was reduced and strengthens the hydrogen bond between Cyc₁ and CoxB, finally improves electron transfer and the bioleaching process.

CHIP control degradation of mutant ETF:QO through ubiquitylation in late-onset multiple acyl-CoA dehydrogenase deficiency

Late-onset multiple acyl-CoA dehydrogenase deficiency (MADD) is the most common form of lipid storage myopathy. The disease is mainly caused by mutations in electron-transfer flavoprotein dehydrogenase gene (ETFDH), which leads to decreased levels of ETF:QO in skeletal muscle. However, the specific underlying mechanisms triggering such degradation remain unknown. We constructed expression plasmids containing wild type ETF:QO and mutants ETF:QO-A84T, R175H, A215T, Y333C, and cultured patient-derived fibroblasts containing the following mutations in ETFDH: c.250G>A (p.A84T), c.998A>G (p.Y333C), c.770A>G (p.Y257C), c.1254_1257delAACT (p. L418TfsX10), c.524G>A (p.R175H), c.380T>A (p.L127P), and c.892C>T (p.P298S). We used in vitro expression systems and patient-derived fibroblasts to detect stability of ETF:QO mutants then evaluated their interaction with Hsp70 interacting protein CHIP with active/inactive ubiquitin E3 ligase carboxyl terminus using western blot and immunofluorescence staining. This interaction was confirmed in vitro and in vivo by co-immunoprecipitation and immunofluorescence staining. We confirmed the existence two ubiquitination sites in mutant ETF:QO using mass spectrometry (MS) analysis. We found that mutant ETF:QO proteins were unstable and easily degraded in patient fibroblasts and in vitro expression systems by ubiquitin-proteasome pathway, and identified the specific ubiquitin E3 ligase as CHIP, which forms complex to control mutant ETF:QO degradation through poly-ubiquitination. CHIP-dependent degradation of mutant ETF:QO proteins was confirmed by MS and site-directed mutagenesis of ubiquitination sites. Hsp70 is directly involved in this process as molecular chaperone of CHIP. CHIP plays an important role in ubiquitin-proteasome pathway dependent degradation of mutant ETF:QO by working as a chaperone-assisted E3 ligase, which reveals CHIP's potential role in pathological mechanisms of late-onset MADD.

Diagnostic challenges in metabolic myopathies

INTRODUCTION

Metabolic myopathies comprise a clinically etiological diverse group of disorders caused by defects in cellular energy metabolism including the breakdown of carbohydrates and fatty acids, which include glycogen storage diseases and fatty acid oxidation disorders. Their wide clinical spectrum ranges from infantile severe multisystemic disorders to adult-onset myopathies. To suspect in adults these disorders, clinical features such as exercise intolerance and recurrent myoglobinuria need investigation while another group presents fixed weakness and cardiomyopathy as a clinical pattern.

AREAS COVERED

In metabolic myopathies, clinical manifestations are important to guide diagnostic tests used in order to lead to the correct diagnosis. The authors searched in literature the most recent techniques developed. The authors present an overview of the most common phenotypes of Pompe disease and what is currently known about the mechanism of ERT treatment. The most common disorders of lipid metabolism are overviewed, with their possible dietary or supplementary treatments.

EXPERT COMMENTARY

The clinical suspicion is the clue to conduct in-depth investigations in suspected cases of metabolic myopathies that lead to the final diagnosis with biochemical molecular studies and often nowadays by the use of Next Generation Sequencing (NGS) to determine gene mutations.

Riboflavin Deficiency-Implications for General Human Health and Inborn Errors of Metabolism

As an essential vitamin, the role of riboflavin in human diet and health is increasingly being highlighted. Insufficient dietary intake of riboflavin is often reported in nutritional surveys and population studies, even in non-developing countries with abundant sources of riboflavin-rich dietary products. A latent subclinical riboflavin deficiency can result in a significant clinical phenotype when combined with inborn genetic disturbances or environmental and physiological factors like infections, exercise, diet, aging and pregnancy. Riboflavin, and more importantly its derivatives, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), play a crucial role in essential cellular processes including mitochondrial energy metabolism, stress responses, vitamin and cofactor biogenesis, where they function as cofactors to ensure the catalytic activity and folding/stability of flavoenzymes. Numerous inborn errors of flavin metabolism and flavoenzyme function have been described, and supplementation with riboflavin has in many cases been shown to be lifesaving or to mitigate symptoms. This review discusses the environmental, physiological and genetic factors that affect cellular riboflavin status. We describe the crucial role of riboflavin for general human health, and the clear benefits of riboflavin treatment in patients with inborn errors of metabolism.

A Synonymous Variant c.579A>G in the ETFDH Gene Caused Exon Skipping in a Patient With Late-Onset Multiple Acyl-CoA Dehydrogenase Deficiency: A Case Report

Background: Multiple acyl-CoA dehydrogenase deficiency (MADD) is an autosomal recessive disorder characterized by a wide range of clinical features, including muscle weakness, hypoglycemia, metabolic acidosis, and multisystem dysfunctions. Loss-of-function mutations in the electron transfer flavoprotein dehydrogenase (ETFDH) gene are associated with MADD. Disease-causing synonymous variants in the ETFDH gene have not been reported so far. Methods: We reported the clinical course of a Chinese girl who was diagnosed with late-onset MADD by the whole exome sequencing. The effects of variants on mRNA splicing were analyzed through transcript analysis in vivo and minigene splice assay in vitro. Results: The 6-month-old girl initially showed muscle weakness, muscular hypotonia, mild myogenic damage, and fatty liver. The blood and urine metabolic screening by tandem mass spectrometry suggested MADD. Molecular analysis of ETFDH gene revealed two novel heterozygous variants, a frameshift mutation c.1812delG (p.V605Yfs^*34) in exon 13 and a synonymous variant c.579A>G (p.E193E) in exon 5. The transcript analysis in vivo exhibited that the synonymous variant c.579A>G caused exon 5 skipping. The minigene splice assay in vitro confirmed the alteration of ETFDH mRNA splicing which could lead to the production of a truncated protein. Supplementation of riboflavin, carnitine and low-fat diet improved the clinical symptoms. Conclusion: We firstly report a rare case of MADD with a pathogenic synonymous variant in the ETFDH gene which highlights the importance and necessity of bioinformatic analysis and functional testing for synonymous variants when searching for causative gene mutations. The results expand the spectrum of pathogenic variants in MADD.

Metabolic lipid muscle disorders: biomarkers and treatment

Lipid storage myopathies (LSMs) are metabolic disorders of the utilization of fat in muscles due to several different defects. In this review, a molecular update of LSMs is presented and recent attempts of finding treatment options are discussed. The main topics discussed are: primary carnitine deficiency, riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency, neutral lipid storage disorders and carnitine palmitoyl transferase deficiency. The most frequent presentations and genetic abnormalities are summarized. We present their diagnosis utilizing biomedical and morphological biomarkers and possible therapeutic interventions. The treatment of these metabolic disorders is a subject of active translational research but appears, in some cases, still elusive.

ETF-QO Mutants Uncoupled Fatty Acid β-Oxidation and Mitochondrial Bioenergetics Leading to Lipid Pathology

The electron-transfer flavoprotein dehydrogenase gene (ETFDH) that encodes the ETF-ubiquinone oxidoreductase (ETF-QO) has been reported to be the major cause of multiple acyl-CoA dehydrogenase deficiency (MADD). ETF-QO is an electron carrier that mainly functions in mitochondrial fatty acid β-oxidation and the delivery of electrons to the ubiquinone pool in the mitochondrial respiratory chain. A high frequency of c.250G>A has been found in Taiwanese patients with late-onset MADD. We postulated that the ETFDH c.250G>A mutation may concomitantly impair fatty acid β-oxidation and mitochondrial function. Using MADD patient-derived lymphoblastoid cells and specifically overexpressed ETFDH c.92C>T, c.250G>A, or coexisted c.92C>T and c.250G>A (c.92C>T + c.250G>A) mutated lymphoblastoid cells, we addressed the genotype-phenotype relationship of ETFDH variation in the pathogenesis of MADD. The decreased adenosine triphosphate synthesis, dissipated mitochondrial membrane potentials, reduced mitochondrial bioenergetics, and increased neutral lipid droplets and lipid peroxides were found in the MADD patient-derived lymphoblastoid cells. Riboflavin and/or coenzyme Q10 supplementation rescued cells from lipid droplet accumulation. All three mutant types, c.92C>T, c.250G>A, or c.92C>T + c.250G>A, had increased lipid droplet accumulation after treatment with palmitic acid. These results help to clarify the molecular pathogenesis of MADD as a result of the high frequency of the ETFDH c.250G>A and c.92C>T mutations.

Characterization of two ETFDH mutations in a novel case of riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency

BACKGROUND

Deficiency of electron transfer flavoprotein dehydrogenase (ETFDH) is associated with multiple acyl-CoA dehydrogenase deficiency (MADD). This disorder is an autosomal recessive lipid storage myopathy (LSM) that exhibits a wide range of clinical features, including myopathy, weakness and multisystem dysfunctions. Many patients with late onset of MADD improve when treated with riboflavin and are also referred to as RR-MADD (riboflavin-responsive multiple Acyl-CoA dehydrogenase disorder).

METHODS

In this study, we report the clinical and genetic characterization of a novel RR-MADD patient. Biochemical data were obtained from analysis of muscle and plasma samples. DNA and RNA were extracted from peripheral blood, and sequence analysis and expression study of ETFDH gene were performed. Finally, the impact of mutations on ETFDH folding was evaluated using bioinformatic tools.

RESULTS

Patient initially presented with vomiting, muscle weakness, and acidosis. Muscle biopsy revealed typical myopathological patterns of lipid storage myopathy and blood acylcarnitine profiles showed a combined elevation of long and medium chain acylcarnitines, supporting the diagnosis of RR-MADD. Molecular analysis of ETFDH gene revealed two heterozygous mutations, a novel splice variation in intron 10, c.1285 + 1G > A, and the previously reported c.560C > T missense mutation. RT-PCR analysis showed an alteration of ETFDH RNA splicing which in turn should lead to the production of a truncated protein. The in silico prediction analysis of ETFDH tridimensional structure demonstrated that the missense mutation resulted in instability and loss of protein activation, while the splice site variation induced a dramatic conformational change of the truncated protein. After MCT diet supplemented with carnitine and riboflavin, the patient showed significant biochemical and clinical improvement, in spite of severe molecular defect.

CONCLUSION

This case report extends the spectrum of ETFDH mutations in MADD, providing further evidence that patients presenting at least one missense mutation in the FAD-binding domain may respond to either carnitine or riboflavin treatment, due to the recovery of some enzymatic activity.

ETFDH Mutations and Flavin Adenine Dinucleotide Homeostasis Disturbance Are Essential for Developing Riboflavin-Responsive Multiple Acyl-Coenzyme A Dehydrogenation Deficiency

OBJECTIVE

Riboflavin-responsive multiple acyl-coenzyme A dehydrogenation deficiency (RR-MADD) is an inherited fatty acid metabolism disorder mainly caused by genetic defects in electron transfer flavoprotein-ubiquinone oxidoreductase (ETF:QO). The variant ETF:QO protein folding deficiency, which can be corrected by therapeutic dosage of riboflavin supplement, has been identified in HEK-293 cells and is believed to be the molecular mechanism of this disease. To verify this hypothesis in vivo, we generated Etfdh ^(h)A84T knockin (KI) mice.

METHODS

Tissues from these mice as well as muscle biopsies and fibroblasts from 7 RR-MADD patients were used to examine the flavin adenine dinucleotide (FAD) concentration and ETF:QO protein amount.

RESULTS

All of the homozygous KI mice (Etfdh ^{(h)A84T/(h)A84T} , KI/KI) were initially normal. After being given a high-fat and vitamin B₂ -deficient (HF-B₂ D) diet for 5 weeks, they developed weight loss, movement ability defects, lipid storage in muscle and liver, and elevated serum acyl-carnitine levels, which are clinically and biochemically similar to RR-MADD patients. Both ETF:QO protein and FAD concentrations were significantly decreased in tissues of HF-B₂ D-KI/KI mice and in cultured fibroblasts from RR-MADD patients. After riboflavin treatment, ETF:QO protein increased in proportion to elevated FAD concentrations, but not related to mRNA levels. These results were further confirmed in cultured fibroblasts from RR-MADD patients.

INTERPRETATION

For the first time, we successfully developed a RR-MADD mice model and confirmed that FAD homeostasis disturbances played a crucial role on the pathomechanism of RR-MADD in this mouse model and culture cells from patients. Supplementation of riboflavin may stabilize variant ETF:QO protein by rebuilding FAD homeostasis. Ann Neurol 2018;84:667-681.

Novel ETFDH mutations in four cases of riboflavin responsive multiple acyl-CoA dehydrogenase deficiency

Multiple acyl-CoA dehydrogenase deficiency (MADD) is an autosomal recessive disorder of fatty acid, amino acid, and choline metabolism caused by mutations in EFTA, EFTB, or ETFDH. Many MADD patients are responsive to treatment with riboflavin, termed riboflavin-responsive MADD (RR-MADD). Here, we report three novel mutations and one previously reported mutation in ETFDH in four RR-MADD patients who presented at various ages, and characterize the corresponding changes in ETF-QO protein structure. Clinicians should consider MADD in the differential diagnosis when patients present with muscle weakness and biochemical abnormalities. Gene testing plays a critical role in confirming the diagnosis of MADD, and may not only prevent patients from invasive testing, but also allow timely initiation of riboflavin treatment. The novel variants in ETFDH and the corresponding clinical features reported here enrich the allelic heterogeneity of RR-MADD and provide insight into genotype-phenotype relationships.

Patient with multiple acyl-CoA dehydrogenase deficiency disease and ETFDH mutations benefits from riboflavin therapy: a case report

Background

Lipid storage myopathy (LSM) is a diverse group of lipid metabolic disorders with great variations in the clinical phenotype and age of onset. Classical multiple acyl-CoA dehydrogenase deficiency (MADD) is known to occur secondary to mutations in electron transfer flavoprotein dehydrogenase (ETFDH) gene. Whole exome sequencing (WES) with clinical correlations can be useful in identifying genomic alterations for targeted therapy.

Case presentation

We report a patient presented with severe muscle weakness and exercise intolerance, suggestive of LSM. Diagnostic testing demonstrated lipid accumulation in muscle fibres and elevated plasma acyl carnitine levels. Exome sequencing of the proband and two of his unaffected siblings revealed compound heterozygous mutations, c.250G > A (p.Ala84Thr) and c.770A > G (p.Tyr257Cys) in the ETFDH gene as the probable causative mutations. In addition, a previously unreported variant c.1042C > T (p.Arg348Trp) in ACOT11 gene was found. This missense variant was predicted to be deleterious but its association with lipid storage in muscle is unclear. The diagnosis of MADD was established and the patient was treated with riboflavin which resulted in rapid clinical and biochemical improvement.

Conclusions

Our findings support the role of WES as an effective tool in the diagnosis of highly heterogeneous disease and this has important implications in the therapeutic strategy of LSM treatment.

Electronic supplementary material

The online version of this article (10.1186/s12920-018-0356-8) contains supplementary material, which is available to authorized users.

Compound heterozygous mutations in electron transfer flavoprotein dehydrogenase identified in a young Chinese woman with late-onset glutaric aciduria type II

Background

Glutaric aciduria type II (GA II) is an autosomal recessive disorder affecting fatty acid and amino acid metabolism. The late-onset form of GA II disorder is almost exclusively associated with mutations in the electron transfer flavoprotein dehydrogenase (ETFDH) gene. Till now, the clinical features of late-onset GA II vary widely and pose a great challenge for diagnosis. The aim of the current study is to characterize the clinical phenotypes and genetic basis of a late-onset GAII patient.

Methods

In this study, we described the clinical and biochemical manifestations of a 23-year-old female Chinese patient with late-onset GA II, and performed genomic DNA-based PCR amplifications and sequence analysis of ETFDH gene of the whole pedigree. We also used in-silicon tools to analyze the mutation and evaluated the pathogenicity of the mutation according to the criteria proposed by American College of Medical Genetics and Genomics (ACMG).

Results

The muscle biopsy of this patient revealed lipid storage myopathy. Blood biochemical test and urine organic acid analyses were consistent with GA II. Direct sequence analysis of the ETFDH gene (NM_004453) revealed compound heterozygous mutations: c.250G > A (p.A84T) on exon 3 and c.920C > G (p.S307C) on exon 8. Both mutations were classified as “pathogenic” according to ACMG criteria.

Conclusions

In conclusion, our study described the phenotype and genotype of a late-onset GA II patient, reiterating the importance of ETFDH gene screening in these patients.

Electronic supplementary material

The online version of this article (10.1186/s12944-017-0576-5) contains supplementary material, which is available to authorized users.

Oxidative Phosphorylation System in Gastric Carcinomas and Gastritis

Switching of cellular energy production from oxidative phosphorylation (OXPHOS) by mitochondria to aerobic glycolysis occurs in many types of tumors. However, the significance of this switching for the development of gastric carcinoma and what connection it may have to Helicobacter pylori infection of the gut, a primary cause of gastric cancer, are poorly understood. Therefore, we investigated the expression of OXPHOS complexes in two types of human gastric carcinomas ("intestinal" and "diffuse"), bacterial gastritis with and without metaplasia, and chemically induced gastritis by using immunohistochemistry. Furthermore, we analyzed the effect of HP infection on several key mitochondrial proteins. Complex I expression was significantly reduced in intestinal type (but not diffuse) gastric carcinomas compared to adjacent control tissue, and the reduction was independent of HP infection. Significantly, higher complex I and complex II expression was present in large tumors. Furthermore, higher complex II and complex III protein levels were also obvious in grade 3 versus grade 2. No differences of OXPHOS complexes and markers of mitochondrial biogenesis were found between bacterially caused and chemically induced gastritis. Thus, intestinal gastric carcinomas, but not precancerous stages, are frequently characterized by loss of complex I, and this pathophysiology occurs independently of HP infection.

Conformational behavior of flavin adenine dinucleotide: conserved stereochemistry in bound and free states

Metabolic enzymes utilize the cofactor flavin adenine dinucleotide (FAD) to catalyze essential biochemical reactions. Because these enzymes have been implicated in disease pathways, it will be necessary to target them via FAD-based structural analogues that can either activate/inhibit the enzymatic activity. To achieve this, it is important to explore the conformational space of FAD in the enzyme-bound and free states. Herein, we analyze X-ray crystallographic data of the enzyme-bound FAD conformations and sample conformations of the molecule in explicit water by molecular dynamics (MD) simulations. Enzyme-bound FAD conformations segregate into five distinct groups based on dihedral angle principal component analysis (PCA). A notable feature in the bound FADs is that the adenine base and isoalloxazine ring are oppositely oriented relative to the pyrophosphate axis characterized by near trans hypothetical dihedral angle "δV" values. Not surprisingly, MD simulations in water show final compact but not perfectly stacked ring structures in FAD. Simulation data did not reveal noticeable changes in overall conformational dynamics of the dinucleotide in reduced and oxidized forms and in the presence and/or absence of ions. During unfolding-folding dynamics, the riboflavin moiety is more flexible than the adenosine monophosphate group in the molecule. Conversely, the isoalloxazine ring is more stable than the variable adenine base. The pyrophosphate group depicts an unusually highly organized fluctuation illustrated by its dihedral angle distribution. Conformations sampled from enzymes and MD are quantified. The extent to which the protein shifts the distribution from the unbound state is discussed in terms of prevalent FAD shapes and dihedral angle population.

Clinical features and ETFDH mutation spectrum in a cohort of 90 Chinese patients with late-onset multiple acyl-CoA dehydrogenase deficiency

The major cause of lipid storage myopathies (LSM) in China is multiple acyl-CoA dehydrogenase deficiency (MADD) caused by ETFDH mutations. We here present an analysis of the spectrum of ETFDH mutations in the largest cohort of patients with MADD (90 unrelated patients). We identified 61 ETFDH mutations, including 31 novel mutations, which were widely distributed within the coding sequence. Three frequent mutations were identified: c.250G > A (most common in South China), c.770A > G and c.1227A > C (most common in both South and North China). Regional differences of allele frequency and further haplotype analysis suggest the possibility of founder effects of c.250G > A and c.770A > G. These findings promise to provide the basis for implementing a rapid and economical strategy for diagnosing MADD.

Multiple Acyl-CoA Dehydrogenation Deficiency (Glutaric Aciduria Type II) with a Novel Mutation of Electron Transfer Flavoprotein-Dehydrogenase in a Cat

Multiple acyl-CoA dehydrogenation deficiency (MADD; also known as glutaric aciduria type II) is a human autosomal recessive disease classified as one of the mitochondrial fatty-acid oxidation disorders. MADD is caused by a defect in the electron transfer flavoprotein (ETF) or ETF dehydrogenase (ETFDH) molecule, but as yet, inherited MADD has not been reported in animals. Here we present the first report of MADD in a cat. The affected animal presented with symptoms characteristic of MADD including hypoglycemia, hyperammonemia, vomiting, diagnostic organic aciduria, and accumulation of medium- and long-chain fatty acids in plasma. Treatment with riboflavin and L-carnitine ameliorated the symptoms. To detect the gene mutation responsible for MADD in this case, we determined the complete cDNA sequences of feline ETFα, ETFβ, and ETFDH. Finally, we identified the feline patient-specific mutation, c.692T>G (p.F231C) in ETFDH. The affected animal only carries mutant alleles of ETFDH. p.F231 in feline ETFDH is completely conserved in eukaryotes, and is located on the apical surface of ETFDH, receiving electrons from ETF. This study thus identified the mutation strongly suspected to have been the cause of MADD in this cat.

Fatty Acid oxidation disorders in a chinese population in taiwan

BACKGROUND

Fatty acid oxidation (FAO) disorders are a heterogeneous group of inborn errors in the transportation and oxidation of fatty acids. FAO disorders were thought to be very rare in the Chinese population. Newborn screening for FAO disorders beginning in 2002 in Taiwan may have increased the diagnosis of this group of diseases.

MATERIALS AND METHODS

Till 2012, the National Taiwan University Hospital Newborn Screening Center screened more than 800,000 newborns for FAO disorders. Both patients diagnosed through screening and patients detected after clinical manifestations were included in this study.

RESULTS

A total of 48 patients with FAO disorders were identified during the study period. The disorders included carnitine palmitoyltransferase I deficiency, carnitine acylcarnitine translocase deficiency, carnitine palmitoyltransferase II deficiency, very long-chain acyl-CoA dehydrogenase deficiency, medium-chain acyl-CoA dehydrogenase deficiency, multiple acyl-CoA dehydrogenase deficiency, short-chain defects, and carnitine uptake defect. Thirty-nine patients were diagnosed through newborn screening. Five false-negative newborn screening cases were noted during this period, and four patients who were not screened were diagnosed based on clinical manifestations. The ages of all patients ranged from 6 months to 22.9 years (mean age 6.6 years). Except for one case of postmortem diagnosis, there were no other mortalities.

CONCLUSIONS

The combined incidence of FAO disorders estimated by newborn screening in the Chinese population in Taiwan is 1 in 20,271 live births. Newborn screening also increases the awareness of FAO disorders and triggers clinical diagnoses of these diseases.

Molecular mechanisms of riboflavin responsiveness in patients with ETF-QO variations and multiple acyl-CoA dehydrogenation deficiency

Riboflavin-responsive forms of multiple acyl-CoA dehydrogenation deficiency (RR-MADD) have been known for years, but with presumed defects in the formation of the flavin adenine dinucleotide (FAD) co-factor rather than genetic defects of electron transfer flavoprotein (ETF) or electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO). It was only recently established that a number of RR-MADD patients carry genetic defects in ETF-QO and that the well-documented clinical efficacy of riboflavin treatment may be based on a chaperone effect that can compensate for inherited folding defects of ETF-QO. In the present study, we investigate the molecular mechanisms and the genotype-phenotype relationships for the riboflavin responsiveness in MADD, using a human HEK-293 cell expression system. We studied the influence of riboflavin and temperature on the steady-state level and the activity of variant ETF-QO proteins identified in patients with RR-MADD, or non- and partially responsive MADD. Our results showed that variant ETF-QO proteins associated with non- and partially responsive MADD caused severe misfolding of ETF-QO variant proteins when cultured in media with supplemented concentrations of riboflavin. In contrast, variant ETF-QO proteins associated with RR-MADD caused milder folding defects when cultured at the same conditions. Decreased thermal stability of the variants showed that FAD does not completely correct the structural defects induced by the variation. This may cause leakage of electrons and increased reactive oxygen species, as reflected by increased amounts of cellular peroxide production in HEK-293 cells expressing the variant ETF-QO proteins. Finally, we found indications of prolonged association of variant ETF-QO protein with the Hsp60 chaperonin in the mitochondrial matrix, supporting indications of folding defects in the variant ETF-QO proteins.