Sensory neuropathy as a manifestation of multiple acyl-coenzyme A dehydrogenase deficiency

Multiple acyl-coenzyme A dehydrogenase deficiency (MADD) is a rare metabolic disorder which typically manifests with muscle weakness. However, despite late-onset MADD being treatable, it is often misdiagnosed, due in part to the heterogeneity of presentations. We report a case of late-onset MADD manifesting first as a sensory neuropathy before progressing to myopathic symptoms and acute metabolic decompensation. Early diagnostic workup with acylcarnitine profiling and organic acid analysis was critical in patient outcome; metabolic decompensation and myopathic symptoms were completely reversed with riboflavin supplementation and dietary modification, although sensory neuropathy persisted. Clinical consideration of MADD as part of the differential diagnosis of neuropathy with myopathy is crucial for a timely diagnosis and treatment of MADD.

The male-to-female ratio in late-onset multiple acyl-CoA dehydrogenase deficiency: a systematic review and meta-analysis

BACKGROUND

Late-onset multiple acyl-CoA dehydrogenase deficiency (MADD) is the most common lipid storage myopathy. There are sex differences in fat metabolism and it is not known whether late-onset MADD affects men and women equally.

METHODS

In this systematic review and meta-analysis, the PubMed, Embase, Web of Science, CNKI, CBM, and Wanfang databases were searched until 01/08/2023. Studies reporting sex distribution in patients with late-onset MADD were included. Two authors independently screened studies for eligibility, extracted data, and assessed risk of bias. Pre-specified outcomes of interest were the male-to-female ratio (MFR) of patients with late-onset MADD, the differences of clinical characteristics between the sexes, and factors influencing the MFR.

RESULTS

Of 3379 identified studies, 34 met inclusion criteria, yielding a total of 609 late-onset MADD patients. The overall pooled percentage of males was 58% (95% CI, 54-63%) with low heterogeneity across studies (I2 = 2.99%; P = 0.42). The mean onset ages, diagnostic delay, serum creatine kinase (CK), and allelic frequencies of 3 hotspot variants in ETFDH gene were similar between male and female patients (P > 0.05). Meta-regressions revealed that ethnic group was associated with the MFR in late-onset MADD, and subgroup meta-analyses demonstrated that East-Asian patients had a higher percentage of male, lower CK, and higher proportion of hotspot variants in ETFDH gene than non-East-Asian patients (P < 0.05).

CONCLUSIONS

Male patients with late-onset MADD were more common than female patients. Ethnicity was proved to be a factor influencing the MFR in late-onset MADD. These findings suggest that male sex may be a risk factor for the disease.

An ETFDH-driven metabolon supports OXPHOS efficiency in skeletal muscle by regulating coenzyme Q homeostasis

Coenzyme Q (Q) is a key lipid electron transporter, but several aspects of its biosynthesis and redox homeostasis remain undefined. Various flavoproteins reduce ubiquinone (oxidized form of Q) to ubiquinol (QH2); however, in eukaryotes, only oxidative phosphorylation (OXPHOS) complex III (CIII) oxidizes QH2 to Q. The mechanism of action of CIII is still debated. Herein, we show that the Q reductase electron-transfer flavoprotein dehydrogenase (ETFDH) is essential for CIII activity in skeletal muscle. We identify a complex (comprising ETFDH, CIII and the Q-biosynthesis regulator COQ2) that directs electrons from lipid substrates to the respiratory chain, thereby reducing electron leaks and reactive oxygen species production. This metabolon maintains total Q levels, minimizes QH2-reductive stress and improves OXPHOS efficiency. Muscle-specific Etfdh-/- mice develop myopathy due to CIII dysfunction, indicating that ETFDH is a required OXPHOS component and a potential therapeutic target for mitochondrial redox medicine.

Riboflavin-responsive lipid-storage myopathy in elderly patients

There are scarce reports of riboflavin-responsive lipid storage myopathy in elderly patients with onset in their sixties. We describe three elderly patients with riboflavin-responsive lipid-storage myopathy. All three patients (aged 67-71 years on first examination) had subacute onset of neck extensors and proximal limb weakness progressing to inability to rise from a sitting position or to walk. Muscle biopsies showed vacuoles with lipid content, mainly in type 1 fibers. Genetic analysis failed to identify any pathogenic variant in one patient, identified a heterozygous variant of uncertain significance c.812 A > G; p.Tyr271Cys in the ETFDH gene in the second patient, and revealed a heterozygote likely pathogenic variant c.1286-2 A > C in the ETFDH gene predicted to cause abnormal splicing in the third patient. All patients responded to treatment with riboflavin and carnitine, and regained normal strength. This report emphasizes the importance of muscle biopsy in revealing treatable lipid storage myopathy in elderly patients with progressive myopathy of unidentifiable cause.

A case report on multiple acyl-CoA dehydrogenase deficiency with severe myopathy and osteoporosis

A 35-year-old male patient presented fluctuating bilateral lower extremity weakness for 3 years. Physical examination showed grade 4 proximal muscle weakness in both lower extremities and grade 5 distal muscle weakness. Laboratory data revealed elevated creatine kinase, triglycerides, and cholesterol. Muscle pathology showed deposition of lipid droplet under the sarcolemma. Bone densitometry indicated severe osteoporosis. Next-generation sequencing revealed a pathogenic mutation in the ETFDH gene. The patient was diagnosed with late-onset multiple acyl-CoA dehydrogenase deficiency. After riboflavin treatment, symptoms of the patient were relieved, physical endurance was restored, and bone mineral density was improved.

High-fat diet increases electron transfer flavoprotein synthesis and lipid respiration in skeletal muscle during exercise training in female mice

High-fat diet (HFD) and exercise remodel skeletal muscle mitochondria. The electron transfer flavoproteins (ETF) transfer reducing equivalents from β-oxidation into the electron transfer system. Exercise may stimulate the synthesis of ETF proteins to increase lipid respiration. We determined mitochondrial remodeling for lipid respiration through ETF in the context of higher mitochondrial abundance/capacity seen in female mice. We hypothesized HFD would be a greater stimulus than exercise to remodel ETF and lipid pathways through increased protein synthesis alongside increased lipid respiration. Female C57BL/6J mice (n = 15 per group) consumed HFD or low-fat diet (LFD) for 4 weeks then remained sedentary (SED) or completed 8 weeks of treadmill training (EX). We determined mitochondrial lipid respiration, RNA abundance, individual protein synthesis, and abundance for ETFα, ETFβ, and ETF dehydrogenase (ETFDH). HFD increased absolute and relative lipid respiration (p = 0.018 and p = 0.034) and RNA abundance for ETFα (p = 0.026), ETFβ (p = 0.003), and ETFDH (p = 0.0003). HFD increased synthesis for ETFα and ETFDH (p = 0.0007 and p = 0.002). EX increased synthesis of ETFβ and ETFDH (p = 0.008 and p = 0.006). Higher synthesis rates of ETF were not always reflected in greater protein abundance. Greater synthesis of ETF during HFD indicates mitochondrial remodeling which may contribute higher mitochondrial lipid respiration through enhanced ETF function.

Late-onset multiple acyl-CoA dehydrogenase deficiency: an insidious presentation

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare inborn error of metabolism that results in impairment of mitochondrial β-oxidation of fatty acids. It is inherited in an autosomal recessive manner and impairs electron transfer in the electron transport chain. The clinical manifestations of MADD are highly variable and include exercise intolerance, myopathy, cardiomyopathy, encephalopathy, coma and death. Early-onset MADD is often associated with a high mortality with significant number of patients presenting with severe metabolic acidosis, non-ketotic hypoglycaemia and/or hyperammonaemic presentations. While late-onset MADD is suggested to have a lower mortality, the severe encephalopathic presentations may well be under-reported as a diagnosis of MADD may not be considered.MADD is treatable with riboflavin and appropriate nutrition with a focus on prevention and early management of metabolic decompensation. The neonatal phenotype differs significantly from late-onset MADD, where diagnosis may be delayed due to heterogeneity in clinical features, atypical presentation and confounding comorbidities, together with lower awareness among physicians.This report describes a woman in her 30s who presented with acute-onset ataxia, confusion and hyperammonaemic encephalopathy requiring intubation. Subsequent biochemical investigation revealed a diagnosis of MADD. At present, there are no national guidelines in Australia for the management of MADD. This case highlights the investigation and treatment of late-onset MADD.

Generation of a human induced pluripotent stem cell line (LZUSHi002-A) from a MADD patient with ETFDH mutation

Multiple acyl-coenzyme A dehydrogenase deficiency (MADD) is an inborn metabolic disorder that affects fatty acid oxidation and the catabolism of branched-chain amino acids, vitamins B and energy metabolism. In this study, the induced pluripotent stem cell (iPSC) line LZUSHi002-A from PBMCs of a 10-year-old male patient with ETFDH mutations using the episomal plasmids was established, which is an ideal in vitro model to understand the exact pathogenesis of MADD.

Electron Transfer Flavoprotein (ETF) α Controls Blood Vessel Development by Regulating Endothelial Mitochondrial Bioenergetics and Oxygen Consumption

While impairment of vascular homeostasis induced by hypercholesterolemia is the first step of cardiovascular diseases, the molecular mechanism behind such impairment is not well known. Here, we reported that high-cholesterol diet (HCD) induced defective vessel sprouting in zebrafish larvae. Electron transfer flavoprotein subunit α (ETFα) (encoded by the ETFA gene), a protein that mediates transfer of electrons from a series of mitochondrial flavoenzymes to the respiratory chain, was downregulated in HCD-fed zebrafish and in endothelial cells treated with oxidized low-density lipoprotein. Knockdown of ETFα with morpholino antisense oligonucleotides reproduced vascular sprouting defects in zebrafish larvae, while replenishing with exogeneous ETFA mRNA could successfully rescue these defects. ETFA knockdown in endothelial cells reduces cell migration, proliferation, and tube formation in vitro. Finally, knockdown of ETFA in endothelial cells also reduced fatty acid oxidation, oxygen consumption rate, and hypoxia-inducible factor-1α (HIF1α) protein levels. Taken together, we demonstrate that downregulation of ETFα is involved in hypercholesterolemia-induced defective vessel sprouting in zebrafish larvae via inhibition of endothelial proliferation and migration. The molecular mechanism behind this phenomenon is the decrease of HIF1α induced by downregulation of ETFα in endothelial cells. This work suggests that disturbance of ETFα-mediated oxygen homeostasis is one of the mechanisms behind hypercholesterolemia-induced vascular dysfunction.

The role of the electron-transfer flavoprotein: ubiquinone oxidoreductase following carbohydrate starvation in Arabidopsis cell cultures

KEY MESSAGE

The functional absence of the electron-transfer flavoprotein: ubiquinone oxidoreductase (ETFQO) directly impacts electrons donation to the mitochondrial electron transport chain under carbohydrate-limiting conditions without major impacts on the respiration of cell cultures. Alternative substrates (e.g., amino acids) can directly feed electrons into the mitochondrial electron transport chain (mETC) via the electron transfer flavoprotein/electron-transfer flavoprotein: ubiquinone oxidoreductase (ETF/ETFQO) complex, which supports plant respiration during stress situations. By using a cell culture system, here we investigated the responses of Arabidopsis thaliana mutants deficient in the expression of ETFQO (etfqo-1) following carbon limitation and supplied with amino acids. Our results demonstrate that isovaleryl-CoA dehydrogenase (IVDH) activity was induced during carbon limitation only in wild-type and that these changes occurred concomit with enhanced protein content. By contrast, neither the activity nor the total amount of IVDH was altered in etfqo-1 mutants. We also demonstrate that the activities of mitochondrial complexes in etfqo-1 mutants, display a similar pattern as in wild-type cells. Our findings suggest that the defect of ETFQO protein culminates with an impaired functioning of the IVDH, since no induction of IVDH activity was observed. However, the functional absence of the ETFQO seems not to cause major impacts on plant respiration under carbon limiting conditions, most likely due to other alternative electron entry pathways.

The Arabidopsis electron-transfer flavoprotein:ubiquinone oxidoreductase is required during normal seed development and germination

The importance of the alternative donation of electrons to the ubiquinol pool via the electron-transfer flavoprotein/electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) complex has been demonstrated. However, the functional significance of this pathway during seed development and germination remains to be elucidated. To assess the function of this pathway, we performed a detailed metabolic and transcriptomic analysis of Arabidopsis mutants to test the molecular consequences of a dysfunctional ETF/ETFQO pathway. We demonstrate that the disruption of this pathway compromises seed germination in the absence of an external carbon source and also impacts seed size and yield. Total protein and storage protein content is reduced in dry seeds, whilst sucrose levels remain invariant. Seeds of ETFQO and related mutants were also characterized by an altered fatty acid composition. During seed development, lower levels of fatty acids and proteins accumulated in the etfqo-1 mutant as well as in mutants in the alternative electron donors isovaleryl-CoA dehydrogenase (ivdh-1) and d-2-hydroxyglutarate dehydrogenase (d2hgdh1-2). Furthermore, the content of several amino acids was increased in etfqo-1 mutants during seed development, indicating that these mutants are not using such amino acids as alternative energy source for respiration. Transcriptome analysis revealed alterations in the expression levels of several genes involved in energy and hormonal metabolism. Our findings demonstrated that the alternative pathway of respiration mediated by the ETF/ETFQO complex affects seed germination and development by directly adjusting carbon storage during seed filling. These results indicate a role for the pathway in the normal plant life cycle to complement its previously defined roles in the response to abiotic stress.

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.

Modulatory functions of recombinant electron transfer flavoprotein α subunit protein from Haemonchus contortus on goat immune cells in vitro

Suppression and modulation of the host immune response to parasitic nematodes have been extensively studied. In the present study, we cloned and produced recombinant electron transfer flavoprotein α subunit (ETFα) protein from Haemonchus contortus (rHCETFα), a parasitic nematode of small ruminants, and studied the effect of this protein on modulating the immune response of goat peripheral blood mononuclear cells (PBMCs) and monocytes. Immunohistochemical tests verified that the HCETFα protein was localized mainly in the intestinal wall and on the body surface of worms. Immunoblot analysis revealed that rHCETFα was recognized by the serum of goats artificially infected with H. contortus. Immunofluorescence analysis indicated that rHCETFα bound to the surface of PBMCs. rHCETFα was co-incubated with goat PBMCs to observe the immunomodulatory effects exerted by HCETFα on proliferation, apoptosis, cytokine secretion and nitric oxide (NO) production. The results showed that rHCETFα suppressed the proliferation of goat PBMCs stimulated by concanavalin A and induced apoptosis in goat PBMCs. After rHCETFα exposure, IL-2, IL-4, IL-17A and TNF-α expression was markedly reduced, whereas secretion of TGF-β1 was significantly elevated, in goat PBMCs. Moreover, rHCETFα up-regulated NO production in a dose-dependent manner. FITC-dextran internalization assays showed that rHCETFα inhibited phagocytosis of goat monocytes. These results elucidate the interaction between parasites and hosts at the molecular level, suggest a possible immunomodulatory target and contribute to the search for innovative proteins that may be candidate targets for drugs and vaccines.

Neonatal-onset multiple acyl-CoA dehydrogenase deficiency (MADD) in the ETFDH gene: A case report and a literature review

RATIONALE

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare inborn error of metabolism affecting fatty acid, amino acid, and choline metabolism. The clinical manifestation of MADD is heterogeneous, from severe neonatal forms to mild late-onset forms.

PATIENT CONCERNS

Here, we report a patient who presented with severe hypoglycemia and exercise intolerance suggestive of MADD. Serum tandem mass spectrometry analysis indicated elevated levels of various acyl carnitines at 25 days of age. Exome sequencing of the proband revealed compound heterozygous mutations, c. 413T>G (p.Leu138Arg) and c.1667C > G (p.Pro556Arg), in the ETFDH gene as the probable causative mutations.

DIAGNOSES

Based on the patient's clinical presentation and test results, the patient was diagnosed with MADD.

INTERVENTIONS

A high-calorie and reduced-fat diet was given together with oral supplements of L-carnitine (150 mg/day).

OUTCOMES

He passed away at the age of 4 months because of severe respiratory distress accompanied by muscle weakness.

LESSONS

He passed away at the age of 4 months because of severe respiratory distress accompanied by muscle weakness. 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 the need for invasive testing but also allow for timely initiation of treatment.

Late-onset MADD: a rare cause of cirrhosis and acute liver failure?

Late-onset multiple acyl-CoA dehydrogenase deficiency (MADD) is a severe inborn error of fat metabolism. In late-onset MADD, hepatopathy in the form of steatosis is commonplace and considered a benign and stable condition that does not progress to more advanced stages of liver disease, however, progression to cirrhosis and acute liver failure (ALF) has been reported in two previous case reports. Here, we report a 22-year-old man, who suffered from late-onset MADD and died from cirrhosis and ALF. In the span of three months repeated clinical examinations, blood tests, and diagnostic imaging as well as liver biopsy revealed rapid progression of hepatopathy from steatosis to decompensated cirrhosis with portal hypertension. Routine studies for recognized etiologies found no evident cause besides MADD. This case report supports the findings of the two previous case reports and adds further evidence to the suggestion that late-onset MADD should be considered a rare cause of cirrhosis and ALF.

Multiple acyl-coenzyme A dehydrogenase deficiency shows a possible founder effect and is the most frequent cause of lipid storage myopathy in Iran

INTRODUCTION

Multiple acyl-coenzyme A dehydrogenase deficiency disorder (MADD) is a relatively rare disorders of lipid metabolism. This study aimed to investigate the demographic, clinical, and genetic features of MADD in Iran.

METHODS

Twenty-nine patients with a definite diagnosis of lipid storage myopathy were recruited. All patients were tested for mutation in the ETFDH gene, and 19 had a biallelic mutation in this gene.

RESULTS

Of 19 patients with definite mutations, 11 (57.9%) were female, and the median age was 31 years. Twelve patients had c.1130 T > C (p.L377P) mutation in exon 10. Two patients had two novel heterozygote pathogenic variants (c.679C > T (p.P227S) in exon 6 and c.814G > A (p.G272R) in exon 7) and two patients had c.1699G > A (p.E567K) in exon 13. Before treatment, the median muscle power was 4.6 (IQR: 4-4.7) that increased to 5 (IQR: 5-5) after treatment (Z = -3.71, p = .000). The median CK was 1848 U/l (IQR: 1014-3473) before treatment, which declined to 188 U/l (IQR: 117-397) after treatment (Z = -3.41, p = .001). Sixteen patients (84.2%) had full recovery after the treatment. The disease onset was earlier (12 years of age; IQR: 6-18) in patients with homozygous c.1130 T > C; p.(L377P) mutation compared to other ETFDH mutations (30 years of age; IQR: 20-35) (p = .00).

DISCUSSION

MADD has different clinical presentations. As the patients respond favorably to treatment, early diagnosis and treatment may prevent the irreversible complications of the disease.

Late-onset riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency (MADD): case reports and epidemiology of ETFDH gene mutations

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a riboflavin-responsive lipid-storage myopathy caused by mutations in the EFTA, EFTB or ETFDH genes. We report a Chinese family of Southern Min origin with two affected siblings with late-onset riboflavin-responsive MADD due to a homozygous c.250G > A EFTDH mutation and review the genetic epidemiology of the c.250G > A mutation.

CASE PRESENTATION

Both siblings presented with exercise-induced myalgia, progressive proximal muscle weakness and high levels of serum muscle enzymes and were initially diagnosed as polymyositis after a muscle biopsy. A repeat biopsy in one sibling subsequently showed features of lipid storage myopathy and genetic analysis identified a homozygous mutation (c.250G > A) in the ETFDH gene in both siblings and carriage of the same mutation by both parents. Glucocorticoid therapy led to improvement in muscle enzyme levels, but little change in muscle symptoms, and only after treatment with riboflavin was there marked improvement in exercise tolerance and muscle strength. The frequency and geographic distribution of the c.250G > A mutation were determined from a literature search for all previously reported cases of MADD with documented mutations. Our study found the c.250G > A mutation is the most common EFTDH mutation in riboflavin-responsive MADD (RR-MADD) and is most prevalent in China and South-East Asia where its epidemiology correlates with the distribution and migration patterns of the southern Min population in Southern China and neighbouring countries.

CONCLUSIONS

Mutations in ETFDH should be screened for in individuals with lipid-storage myopathy to identify patients who are responsive to riboflavin. The c.250G > A mutation should be suspected particularly in individuals of southern Min Chinese background.

Adolescent Hyperuricemia with Lipid Storage Myopathy: A Clinical Study

BACKGROUND In this study, we investigated the clinical and pathological features of patients with lipid storage myopathy (LSM) complicated with hyperuricemia, to improve clinicians' understanding of metabolic multi-muscular disorder with metabolic disorders, and to reduce the risk of missed diagnosis of LSM. MATERIAL AND METHODS From January 2005 to December 2017, 8 patients underwent muscle biopsy and diagnosed by muscle pathology and genetic testing in our hospital. All 8 patients were in compliance with LSM diagnosis. We collected data on the patient's clinical performance, adjuvant examination, treatment, and outcomes to provide a comprehensive report and description of LSM patients with hyperuricemia. RESULTS All patients were diagnosed as having ETFDH gene mutations. The main clinical manifestations of patients were chronic limb and trunk weakness, limb numbness, and muscle pain. The serum creatine kinase (CK) values in all patients were higher than normal values. Electromyography showed 3 cases of simple myogenic damage and 3 cases of neurogenic injury. Hematuria metabolic screening showed that 2 patients had elevated glutaric aciduria, and 1 patient had elevated fatty acyl carnitine in the blood. All patients were given riboflavin treatment, and the clinical symptoms were significantly improved, and 3 patients returned to normal uric acid levels after treatment. Pathological staining showed an abnormal deposition of lipid droplets in muscle fibers. CONCLUSIONS If an adolescent hyperuricemia patient has abnormal limb weakness, exercise intolerance, and elevated serum CK values, clinicians need to be highly alert to the possibility of LSM. Early diagnosis and treatment of LSM should improve the clinical symptoms and quality of life and reduce complications.

[Tandem mass spectrometry analysis and genetic diagnosis of neonates with fatty acid oxidation disorders in central and northern regions of Guangxi]

OBJECTIVE

To determine the incidence and mutational types of fatty acid oxidation disorders (FAOD) in central-northern region of Guangxi.

METHODS

A total of 62 953 neonates were screened for FAOD during December 2012 and December 2017. Acyl-carnitine profiling of neonatal blood sample was performed by tandem mass spectrometry using dry blood spots on a filter paper. The diagnosis of FAOD was confirmed by organic acid profiling of urea and genetic testing.

RESULTS

Eighteen cases of FAOD were diagnosed among the 62 953 neonates. Among these, primary carnitine deficiency (PCD) was the most common type (n=13), which was followed by short-chain acyl-CoA dehydrogenase deficiency (SCADD) (n=2), medium-chain acyl-CoA dehydrogenase deficiency (MCADD) (n=1), multiple acyl-CoA dehydrogenase deficiency (MADD) (n=1), and carnitine palmitoyltransferase II deficiency (CPT II D) (n=1). Genetic testing has revealed two previously unreported variants, i.e., c.337G to A (p.Gly113Arg) of ACADS gene and c.737G TO T (p.Gly246Val) of ETFA gene.

CONCLUSION

PCD is the most common FAOD in central-northern Guangxi. Tandem mass spectrometry combined with genetic testing may facilitate early diagnosis of FAOD.

[Analysis of ETFDH gene variation in a Chinese family affected with lipid storage myopathy]

OBJECTIVE

To detect potential variation in an ethnic Han Chinese family affected with late-onset lipid storage myopathy.

METHODS

Next generation sequencing (NGS) was used to screen disease-related genes in the proband. Suspected mutation was validated with PCR and Sanger sequencing in two patients, their father, and 100 healthy controls.

RESULTS

Heterozygous c.770A>G (p.Tyr257Cys) and c.1395dupT (p.Gly466Tryfs) mutation were detected in the two patients. Their father was found to be heterozygous for the c.770A>G (p.Tyr257Cys) mutation, while the c.1395dupT (p.Gly466Tryfs) variation was not reported previously and not found among the healthy controls.

CONCLUSION

Mutations of the ETFDH gene probably underlie the pathogenesis in this family. The novel c.1395dupT (p.Gly466Tryfs) has enriched the mutation spectrum of EDFDH gene.

Diversity and complexity of flavodiiron NO/O2 reductases

Flavodiiron proteins (FDPs) are a family of enzymes endowed with nitric oxide (NO) or oxygen reductase activities, forming the innocuous nitrous oxide (N2O) or water molecules, respectively. FDPs are widespread in the three life kingdoms, and have a modular nature, being each monomer minimally constituted by a metallo-β-lactamase-like domain containing a catalytic diiron centre, followed by a flavodoxin one, with a flavin mononucleotide. Since their discovery, additional domains have been found in FDPs, attached to the C-terminus, and containing either extra metal (iron) centers or extra flavin binding modules. Following an extensive analysis of genomic databases, we identified novel domain compositions, and proposed a new classification of FDPs in eight classes based on the nature and number of extra domains.

Investigating the mode of action of the redox-active antimalarial drug plasmodione using the yeast model

Malaria is caused by protozoan parasites and remains a major public health issue in subtropical areas. Plasmodione (3-[4-(trifluoromethyl)benzyl]-menadione) is a novel early lead compound displaying fast-acting antimalarial activity. Treatment with this redox active compound disrupts the redox balance of parasite-infected red blood cells. In vitro, the benzoyl analogue of plasmodione can act as a subversive substrate of the parasite flavoprotein NADPH-dependent glutathione reductase, initiating a redox cycling process producing ROS. Whether this is also true in vivo remains to be investigated. Here, we used the yeast model to investigate the mode of action of plasmodione and uncover enzymes and pathways involved in its activity. We showed that plasmodione is a potent inhibitor of yeast respiratory growth, that in drug-treated cells, the ROS-sensitive aconitase was impaired and that cells with a lower oxidative stress defence were highly sensitive to the drug, indicating that plasmodione may act via an oxidative stress. We found that the mitochondrial respiratory chain flavoprotein NADH-dehydrogenases play a key role in plasmodione activity. Plasmodione and metabolites act as substrates of these enzymes, the reaction resulting in ROS production. This in turn would damage ROS-sensitive enzymes leading to growth arrest. Our data further suggest that plasmodione is a pro-drug whose activity is mainly mediated by its benzhydrol and benzoyl metabolites. Our results in yeast are coherent with existing data obtained in vitro and in Plasmodium falciparum, and provide additional hypotheses that should be investigated in parasites.

Long-term outcomes of a patient with late-onset multiple acyl-CoA dehydrogenase deficiency caused by novel mutations in ETFDH: A case report

RATIONALE

Late-onset multiple acyl-coenzyme A dehydrogenase deficiency (MADD) mainly affects the neck extensor muscle group, which has been confirmed by novel mutations in electron-transferring-flavoprotein dehydrogenase (ETFDH). So far, a few cases have been reported with long-term follow-up. Here we report a case of late-onset MADD where the patient was followed up for 8 years during which time he underwent 2 muscle biopsies and 2 pathological examinations and his symptoms were significantly alleviated after appropriate treatments.

PATIENT CONCERNS

In September 2009, a 16-year-old male patient was hospitalized due to gradually increasing difficulty in raising his head and weakness in limb muscles over a 6-month period. During the physical examination, the patient's neck extensor muscle strength was grade III-IV. His proximal limb muscle strength was grade IV, and his distal muscle strength was normal. His blood creatine kinase (CK) was 783 U/L.

DIAGNOSIS

Muscle biopsy revealed a large number of vacuolar fibers, which were mainly type I fibers. These findings were consistent with the diagnosis of lipid storage myopathy (LSM). ETFDH gene test detected C.736G > A at exon 7 and C.920C > G at exon 8.

INTERVENTIONS

Coenzyme Q10 treatment was administered. The first coenzyme Q10 40 mg tid was treated for three months, with the change of coenzyme Q10 20 mg tid for 6 months, followed by the change of coenzyme Q10 10 mg tid for long-term use.

OUTCOMES

The patient's condition significantly improved after 3 months. At 7th year follow-up the patient's blood CK was normal, and a second muscle biopsy revealed no muscle vacuolar fibers and no increase in lipid droplets. Subsequently, the patient was withdrawn from the coenzyme Q10 treatment, and the condition of the patient remained normal.

LESSONS

Muscle biopsy was the main method used to determine LSM. Treatment with riboflavin should be started when the diagnosis of LSM is definitive. Furthermore, ETFDH gene tests should be performed for further classification. Moreover, coenzyme Q10 may be another effective drug for MADD.

[A novel mutation in the ETFDH gene of an infant with multiple acyl-CoA dehydrogenase deficiency]

This article reports the results of tandem mass spectrometry and the mutation features of the ETFDH gene for an infant with multiple acyl-CoA dehydrogenase deficiency. The results of tandem mass spectrometry showed that C14 : 1, C8, C6, C10, and C12 increased. Exon sequencing was performed on this infant and his parents and revealed double heterozygous mutations in the ETFDH gene of the infant: c.992A>T and c.1450T>C. The former was inherited from his mother, and the latter was inherited from his father. c.1450T>C was shown to be the pathogenic mutation in the HGMD database. PolyPhen2, SIFT, and PROVEAN all predicted that the novel mutation c.992A>T might be pathogenic, and the mutant amino acids were highly conserved across various species. The findings expand the mutation spectrum of the ETFDH gene, and provide molecular evidence for the etiological diagnosis of the patient with multiple acyl-CoA dehydrogenase deficiency as well as for the genetic counseling and prenatal diagnosis in the family.

Oxidation of the FAD cofactor to the 8-formyl-derivative in human electron-transferring flavoprotein

The heterodimeric human (h) electron-transferring flavoprotein (ETF) transfers electrons from at least 13 different flavin dehydrogenases to the mitochondrial respiratory chain through a non-covalently bound FAD cofactor. Here, we describe the discovery of an irreversible and pH-dependent oxidation of the 8α-methyl group to 8-formyl-FAD (8f-FAD), which represents a unique chemical modification of a flavin cofactor in the human flavoproteome. Furthermore, a set of hETF variants revealed that several conserved amino acid residues in the FAD-binding pocket of electron-transferring flavoproteins are required for the conversion to the formyl group. Two of the variants generated in our study, namely αR249C and αT266M, cause glutaric aciduria type II, a severe inherited disease. Both of the variants showed impaired formation of 8f-FAD shedding new light on the potential molecular cause of disease development. Interestingly, the conversion of FAD to 8f-FAD yields a very stable flavin semiquinone that exhibited slightly lower rates of electron transfer in an artificial assay system than hETF containing FAD. In contrast, the formation of 8f-FAD enhanced the affinity to human dimethylglycine dehydrogenase 5-fold, indicating that formation of 8f-FAD modulates the interaction of hETF with client enzymes in the mitochondrial matrix. Thus, we hypothesize that the FAD cofactor bound to hETF is subject to oxidation in the alkaline (pH 8) environment of the mitochondrial matrix, which may modulate electron transport between client dehydrogenases and the respiratory chain. This discovery challenges the current concepts of electron transfer processes in mitochondria.

Exome array analysis identifies ETFB as a novel susceptibility gene for anthracycline-induced cardiotoxicity in cancer patients

PURPOSE

Anthracyclines are widely used chemotherapeutic drugs that can cause progressive and irreversible cardiac damage and fatal heart failure. Several genetic variants associated with anthracycline-induced cardiotoxicity (AIC) have been identified, but they explain only a small proportion of the interindividual differences in AIC susceptibility.

METHODS

In this study, we evaluated the association of low-frequency variants with risk of chronic AIC using the Illumina HumanExome BeadChip array in a discovery cohort of 61 anthracycline-treated breast cancer patients with replication in a second independent cohort of 83 anthracycline-treated pediatric cancer patients, using gene-based tests (SKAT-O).

RESULTS

The most significant associated gene in the discovery cohort was ETFB (electron transfer flavoprotein beta subunit) involved in mitochondrial β-oxidation and ATP production (P = 4.16 × 10^-4) and this association was replicated in an independent set of anthracycline-treated cancer patients (P = 2.81 × 10^-3). Within ETFB, we found that the missense variant rs79338777 (p.Pro52Leu; c.155C > T) made the greatest contribution to the observed gene association and it was associated with increased risk of chronic AIC in the two cohorts separately and when combined (OR 9.00, P = 1.95 × 10^-4, 95% CI 2.83-28.6).

CONCLUSIONS

We identified and replicated a novel gene, ETFB, strongly associated with chronic AIC independently of age at tumor onset and related to anthracycline-mediated mitochondrial dysfunction. Although experimental verification and further studies in larger patient cohorts are required to confirm our finding, we demonstrated that exome array data analysis represents a valuable strategy to identify novel genes contributing to the susceptibility to chronic AIC.

[Clinical features and ETFDH mutations of children with late-onset glutaric aciduria type II: a report of two cases]

OBJECTIVE

To investigate the clinical and genetic features of two families with late-onset glutaric aciduria type II caused by ETFDH mutations.

METHODS

Target gene sequence capture and next generation sequencing were used for sequencing of suspected patients and their family members. The patients' clinical features were retrospectively analyzed and literature review was performed.

RESULTS

The probands of the two families had a clinical onset at the ages of 10 years and 5.5 years respectively, with the clinical manifestations of muscle weakness and muscle pain. Laboratory examinations revealed significant increases in the serum levels of creatine kinase, creatine kinase-MB, and lactate dehydrogenase. Tandem mass spectrometry showed increases in various types of acylcarnitines. The analysis of urine organic acids showed an increase in glutaric acid. Electromyography showed myogenic damage in both patients. Gene detection showed two novel mutations in the ETFDH gene (c.1331T>C from the mother and c.824C>T from the father) in patient 1, and the patient's younger brother carried the c.1331T>C mutation but had a normal phenotype. In patient 2, there was a novel mutation (c.177insT from the father) and a known mutation (c.1474T>C from the mother) in the ETFDH gene. Several family members carried such mutations. Both patients were diagnosed with glutaric aciduria type II. Their symptoms were improved after high-dose vitamin B2 treatment.

CONCLUSIONS

For patients with unexplained muscle weakness and pain, serum creatine kinase, acylcarnitines, and urinary organic acids should be measured, and the possibility of glutaric aciduria type II should be considered. Genetic detection is helpful to make a confirmed diagnosis.

New protein-protein interactions of mitochondrial connexin 43 in mouse heart

Connexin 43 (Cx43), the gap junction protein involved in cell-to-cell coupling in the heart, is also present in the subsarcolemmal fraction of cardiomyocyte mitochondria. It has been described to regulate mitochondrial potassium influx and respiration and to be important for ischaemic preconditioning protection, although the molecular effectors involved are not fully characterized. In this study, we looked for potential partners of mitochondrial Cx43 in an attempt to identify new molecular pathways for cardioprotection. Mass spectrometry analysis of native immunoprecipitated mitochondrial extracts showed that Cx43 interacts with several proteins related with mitochondrial function and metabolism. Among them, we selected for further analysis only those present in the subsarcolemmal mitochondrial fraction and known to be related with the respiratory chain. Apoptosis-inducing factor (AIF) and the beta-subunit of the electron-transfer protein (ETFB), two proteins unrelated to date with Cx43, fulfilled these conditions, and their interaction with Cx43 was proven by direct and reverse co-immunoprecipitation. Furthermore, a previously unknown molecular interaction between AIF and ETFB was established, and protein content and sub-cellular localization appeared to be independent from the presence of Cx43. Our results identify new protein-protein interactions between AIF-Cx43, ETFB-Cx43 and AIF-ETFB as possible players in the regulation of the mitochondrial redox state.

Electron Transfer Flavoprotein Subunit Beta Is a Candidate Endothelial Cell Autoantigen in Behçet's Disease

Behçet’s disease (BD) is a chronic inflammatory disease with multisystem involvement, and it is listed as a rare disease in the United States but is common in the Middle East, China, and Japan. The aim of this study was to identify novel autoantigens in Chinese patients with BD. First, the candidate autoantigens were screened by Western blotting, and the sequences of putative antigens were identified by LC-MALDI-TOF/TOF mass spectrometry. Next, the screened protein was cloned, expressed and purified. Then, an optimized ELISA was developed, and the serological criteria were evaluated using a large number of confirmed patients. One antigen with a molecular weight of approximately 28 kDa was identified as electron transfer flavoprotein subunit beta (ETFB). Positive reactivity was detected in recombinant human ETFB sera from 38 of 92 BD patients (41 %) and 1 of 90 healthy controls (1 %).

A proteomics approach to identify the differential protein level in cardiac muscle of diabetic rat

BACKGROUND

Cardiovascular proteomics investigation reveals the characterization and elucidation of the novel therapeutic targets and strategies to prevent the development of heart failure associated diabetic complication by using 2DE and MS.

METHODS

The experimental animals were made diabetic with a single intraperitoneal injection of alloxan (150 mg/kg of bw). Albino rats were randomly divided into four individual groups: Group-I control (n=6), group-II alloxan-induced diabetic rats, untreated (n=6), group-III (n=6) and group-IV (n=6) alloxan-induced diabetic rats were treated with aqueous and ethanolic extracts of Cynodon dactylon for 15 days, respectively. Animals were euthanized to collect the heart tissues and blood samples. 2DE sample preparation, gel running and staining (n=6: each groups) were performed at the same time to avoid variation. The result of six gel images from each group were analyzed and evaluated as one match set with 2D software (P<0.05).

RESULTS

The above experiment revealed two up-regulated proteins in group-II i.e. NTF4 and ETFB.

CONCLUSIONS

NTF4 is a neuro-protective agent for neuro-degenerative diseases. It will prevent diabetic secondary complications, such as diabetic polyneuropathy and cardiomyopathy. ETFB is active in the mitochondria, the energy-producing centres in cells. It is clear from the experiment that because of up-regulation of ETFB more energy is availabile and the electron transfer for heart during diabetes is possible, what leads to reduce the oxidative stress and free-radical formation. The up-regulated proteins reduced CVD that occurred just before overt hyperglycaemia due to administration of C. dactylon. This approach established the preliminary reference map for decoding cellular mechanisms linked between pathogenesis CVD and diabetes.

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.

Multi-organ abnormalities and mTORC1 activation in zebrafish model of multiple acyl-CoA dehydrogenase deficiency

Multiple Acyl-CoA Dehydrogenase Deficiency (MADD) is a severe mitochondrial disorder featuring multi-organ dysfunction. Mutations in either the ETFA, ETFB, and ETFDH genes can cause MADD but very little is known about disease specific mechanisms due to a paucity of animal models. We report a novel zebrafish mutant dark xavier (dxa^vu463) that has an inactivating mutation in the etfa gene. dxa^vu463 recapitulates numerous pathological and biochemical features seen in patients with MADD including brain, liver, and kidney disease. Similar to children with MADD, homozygote mutant dxa^vu463 zebrafish have a spectrum of phenotypes ranging from moderate to severe. Interestingly, excessive maternal feeding significantly exacerbated the phenotype. Homozygous mutant dxa^vu463 zebrafish have swollen and hyperplastic neural progenitor cells, hepatocytes and kidney tubule cells as well as elevations in triacylglycerol, cerebroside sulfate and cholesterol levels. Their mitochondria were also greatly enlarged, lacked normal cristae, and were dysfunctional. We also found increased signaling of the mechanistic target of rapamycin complex 1 (mTORC1) with enlarged cell size and proliferation. Treatment with rapamycin partially reversed these abnormalities. Our results indicate that etfa gene function is remarkably conserved in zebrafish as compared to humans with highly similar pathological, biochemical abnormalities to those reported in children with MADD. Altered mTORC1 signaling and maternal nutritional status may play critical roles in MADD disease progression and suggest novel treatment approaches that may ameliorate disease severity.

Mitochondrial disorders have multiple genetic causes and are usually associated with severe, multi-organ disease. We report a novel zebrafish model of mitochondrial disease by inactivating the etfa gene. Loss of this gene in humans causes multiple acyl-Co dehydrogenase deficiency (MADD) that manifests with brain, liver, heart, and kidney disease. While presentations are variable, many children with MADD have a severe form of the disease that rapidly leads to death. We report that etfa gene function is highly conserved in zebrafish as compared to humans. In addition we uncovered potential disease mechanisms that were previously unknown. These include the impact of maternal nutrition on disease severity in their offspring as well as the role mTOR kinase signaling. Inhibition of this kinase with the drug rapamycin partially reversed some of the symptoms suggesting this may be a new approach to treat mitochondrial disorders.

Increased muscle coenzyme Q10 in riboflavin responsive MADD with ETFDH gene mutations due to secondary mitochondrial proliferation

Multiple acyl-coenzyme A dehydrogenation deficiency (MADD) has a wide range of phenotypic variation ranging from a neonatal lethal form to a mild late-onset form. Our previous data showed that in a group of Chinese patients, a mild type of MADD characterized by myopathy with clinically no other systemic involvement was caused by mutations in electron transfer flavoprotein dehydrogenase (ETFDH) gene, which encodes electron transfer flavoprotein: ubiquinone oxidoreductase (ETF:QO). Coenzyme Q10 (CoQ10), a downstream electron receptor of ETF:QO was first reported deficient in muscle of MADD patients with ETFDH gene mutations. Nevertheless, this result was not confirmed in a recently published study. Therefore to elucidate muscle CoQ10 level in a large group of MADD patients may provide further insight into the pathomechanism and therapeutic strategies. In this study, we found that 34 riboflavin responsive patients with ETFDH gene mutations had an elevated CoQ10 pool in muscle by high performance liquid chromatography (HPLC). However, when CoQ10 levels were normalized to citrate synthase, a marker of mitochondrial mass, there was no significant difference between patients and normal controls. Meanwhile, the increased mitochondrial DNA copy number in muscle also supported that the elevated CoQ10 pool was mainly due to mitochondrial mass proliferation. The expression of CoQ10 biosynthesis genes showed no significant changes whereas genes involved in lipid metabolism, such as PPARα, were marked up regulated. Our results suggested that CoQ10 seems not to be a primary factor in riboflavin responsive MADD and the apparent increase in CoQ10 may be secondary to mitochondrial proliferation.

Secondary coenzyme Q10 deficiency and oxidative stress in cultured fibroblasts from patients with riboflavin responsive multiple Acyl-CoA dehydrogenation deficiency

Coenzyme Q10 (CoQ10) is essential for the energy production of the cells and as an electron transporter in the mitochondrial respiratory chain. CoQ10 links the mitochondrial fatty acid β-oxidation to the respiratory chain by accepting electrons from electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO). Recently, it was shown that a group of patients with the riboflavin responsive form of multiple acyl-CoA dehydrogenation deficiency (RR-MADD) carrying inherited amino acid variations in ETF-QO also had secondary CoQ10 deficiency with beneficial effects of CoQ10 treatment, thus adding RR-MADD to an increasing number of diseases involving secondary CoQ10 deficiency. In this study, we show that moderately decreased CoQ10 levels in fibroblasts from six unrelated RR-MADD patients were associated with increased levels of mitochondrial reactive oxygen species (ROS). Treatment with CoQ10, but not with riboflavin, could normalize the CoQ10 level and decrease the level of ROS in the patient cells. Additionally, riboflavin-depleted control fibroblasts showed moderate CoQ10 deficiency, but not increased mitochondrial ROS, indicating that variant ETF-QO proteins and not CoQ10 deficiency are the causes of mitochondrial ROS production in the patient cells. Accordingly, the corresponding variant Rhodobacter sphaeroides ETF-QO proteins, when overexpressed in vitro, bind a CoQ10 pseudosubstrate, Q10Br, less tightly than the wild-type ETF-QO protein, suggesting that molecular oxygen can get access to the electrons in the misfolded ETF-QO protein, thereby generating superoxide and oxidative stress, which can be reversed by CoQ10 treatment.

Pregnancy of a patient with multiple Acyl-CoA dehydrogenation deficiency (MADD)

We describe the pregnancy of a patient of French-Canadian descent with multiple Acyl-CoA dehydrogenation deficiency (MADD). The proband was found to harbor a previously reported homozygous missense mutation on EFTDH gene (p.Pro534Leu:c.1601C>T) confirming the biochemical diagnosis of MADD. This mutation was not found in 50 controls from the same ethnic background. The clinical and molecular information of all patients with ETFDH mutations reported in the literature up-to-date are summarized.

Mechanism of superoxide and hydrogen peroxide generation by human electron-transfer flavoprotein and pathological variants

Reactive oxygen species production by mitochondrial enzymes plays a fundamental role both in cellular signaling and in the progression of dysfunctional states. However, sources of reactive oxygen species and the mechanisms by which enzymes produce these reactive species still remain elusive. We characterized the generation of reactive oxygen species by purified human electron-transfer flavoprotein (ETF), a mitochondrial enzyme that has a central role in the metabolism of lipids, amino acids, and choline. The results showed that ETF produces significant amounts of both superoxide and hydrogen peroxide in the presence of its partner enzyme medium-chain acyl-CoA dehydrogenase (MCAD). ETF-mediated production of reactive oxygen species is partially inhibited at high MCAD/ETF ratios, whereas it is enhanced at high ionic strength. Determination of the reduction potentials of ETF showed that thermodynamic properties of the FAD cofactor are changed upon formation of a complex between ETF and MCAD, supporting the notion that protein:protein interactions modulate the reactivity of the protein with dioxygen. Two pathogenic ETF variants were also studied to determine which factors modulate the reactivity toward molecular oxygen and promote reactive oxygen species production. The results obtained show that destabilized conformations and defective protein:protein interactions increase the ability of ETF to generate reactive oxygen species. A possible role for these processes in mitochondrial dysfunction in metabolic disorders of fatty acid β-oxidation is discussed.

Primary and secondary CoQ(10) deficiencies in humans

CoQ(10) deficiencies are clinically and genetically heterogeneous. This syndrome has been associated with five major clinical phenotypes: (1) encephalomyopathy, (2) severe infantile multisystemic disease, (3) cerebellar ataxia, (4) isolated myopathy, and (5) nephrotic syndrome. In a few patients, pathogenic mutations have been identified in genes involved in the biosynthesis of CoQ(10) (primary CoQ(10) deficiencies) or in genes not directly related to CoQ(10) biosynthesis (secondary CoQ(10) deficiencies). Respiratory chain defects, ROS production, and apoptosis variably contribute to the pathogenesis of primary CoQ(10) deficiencies.

Novel ETF dehydrogenase mutations in a patient with mild glutaric aciduria type II and complex II-III deficiency in liver and muscle

We describe a 22-year-old male who developed severe hypoglycemia and lethargy during an acute illness at 4 months of age and subsequently grew and developed normally. At age 4 years he developed recurrent vomiting with mild hyperammonemia and dehydration requiring frequent hospitalizations. Glutaric aciduria Type II was suspected based upon biochemical findings and managed with cornstarch, carnitine and riboflavin supplements. He did not experience metabolic crises between ages 4-12 years. He experienced recurrent vomiting, mild hyperammonemia, and generalized weakness associated with acute illnesses and growth spurts. At age 18 years, he developed exercise intolerance and proximal muscle weakness leading to the identification of multiple acyl-CoA dehydrogenase and complex II/III deficiencies in both skeletal muscle and liver. Subsequent molecular characterization of the ETFDH gene revealed novel heterozygous mutations, p.G274X:c.820 G > T (exon 7) and p.P534L: c.1601 C > T (exon 12), the latter within the iron sulfur-cluster and predicted to affect ubiquinone reductase activity of ETFDH and the docking of ETF to ETFDH. Our case supports the concept of a structural interaction between ETFDH and other enzyme partners, and suggests that the conformational change upon ETF binding to ETFDH may play a key role in linking ETFDH to II/III super-complex formation.

Novel mutations in ETFDH gene in Chinese patients with riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD, OMIM 231680) or glutaric aciduria type II (GAII) is an inherited autosomal recessive disease affecting fatty acid, amino acid and choline metabolism, due to mutations in one of three genes namely, electron transfer flavoprotein alpha-subunit, ETFA (OMIM 608053), electron transfer flavoprotein beta-subunit, ETFB (OMIM 130410) and electron transfer flavoprotein dehydrogenase, ETFDH (OMIM 231675). Some MADD patients are responsive to riboflavin treatment with an excellent prognosis. Recently, mutations in ETFDH were found to be responsible for all riboflavin-responsive MADD patients. In this study, we present the clinical features and molecular studies of 2 Chinese families with riboflavin-responsive MADD.

METHODS

Genomic DNA was extracted from peripheral blood samples or skin fibroblast cultures from the patients and normal controls. The thirteen exons of ETFDH were amplified by PCR. PCR products were sequenced in both forward and reverse directions. To rule out mutations in other genes, phenotype segregation was studied in the families by microsatellite markers in the proximity of the 3 genes, ETFA, ETFB and ETFDH.

RESULTS

Four novel mutations in ETFDH were detected in the 2 families. In family 1, a frame shift mutation, c.1355delG which introduced a premature-termination codon (PTC), I454X in exon 11 of ETFDH was found. Another mutation was a c.250G>A transition in exon 3 of ETFDH, A84T. In family 2, two novel missense mutations were identified, P137S, in exon 4 and G467R in exon 11. No carrier of these four mutations was identified from about 150 alleles of healthy Chinese control subjects.

CONCLUSIONS

Four novel mutations (3 missenses and 1 deletion) in ETFDH were found in Chinese families that presented with riboflavin-responsive MADD, which further expands the list of mutations found in patients with riboflavin-responsive MADD. Furthermore, we illustrated the utility of phenotype-genotype segregation in MADD families to prioritize genes for sequencing or to rule out the presence of disease causing mutation in other genes in MADD and other diseases caused by multiple genes.

ETFDH mutations, CoQ10 levels, and respiratory chain activities in patients with riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a metabolic disorder due to dysfunction of electron transfer flavoprotein (ETF) or ETF-ubiquinone oxidoreductase (ETF-QO). Mutations in ETFDH, encoding ETF-QO have been associated with both riboflavin-responsive and non-responsive MADD as well as a myopathic form of CoQ(10) deficiency, although pathomechanisms responsible for these different phenotypes are not well-defined. We performed mutation analysis in four Taiwanese MADD patients. Three novel ETFDH mutations were identified in four patients and all harbored the p.A84T mutation. Muscle CoQ(10) levels and respiratory chain activities measured in two patients were normal. Three patients improved on riboflavin together with carnitine. Our results show that not all MADD patients have CoQ(10) deficiency. Based upon our data, riboflavin and carnitine may be the first-line treatment for MADD.

Evolution of function in the "two dinucleotide binding domains" flavoproteins

Structural and biochemical constraints force some segments of proteins to evolve more slowly than others, often allowing identification of conserved structural or sequence motifs that can be associated with substrate binding properties, chemical mechanisms, and molecular functions. We have assessed the functional and structural constraints imposed by cofactors on the evolution of new functions in a superfamily of flavoproteins characterized by two-dinucleotide binding domains, the “two dinucleotide binding domains” flavoproteins (tDBDF) superfamily. Although these enzymes catalyze many different types of oxidation/reduction reactions, each is initiated by a stereospecific hydride transfer reaction between two cofactors, a pyridine nucleotide and flavin adenine dinucleotide (FAD). Sequence and structural analysis of more than 1,600 members of the superfamily reveals new members and identifies details of the evolutionary connections among them. Our analysis shows that in all of the highly divergent families within the superfamily, these cofactors adopt a conserved configuration optimal for stereospecific hydride transfer that is stabilized by specific interactions with amino acids from several motifs distributed among both dinucleotide binding domains. The conservation of cofactor configuration in the active site restricts the pyridine nucleotide to interact with FAD from the re-side, limiting the flow of electrons from the re-side to the si-side. This directionality of electron flow constrains interactions with the different partner proteins of different families to occur on the same face of the cofactor binding domains. As a result, superimposing the structures of tDBDFs aligns not only these interacting proteins, but also their constituent electron acceptors, including heme and iron-sulfur clusters. Thus, not only are specific aspects of the cofactor-directed chemical mechanism conserved across the superfamily, the constraints they impose are manifested in the mode of protein–protein interactions. Overlaid on this foundation of conserved interactions, nature has conscripted different protein partners to serve as electron acceptors, thereby generating diversification of function across the superfamily.

The sequencing of genomes from different species has provided a unique opportunity for comparative analysis and opened the door to a higher level of understanding of living organisms. However, identifying the biochemical functions of the protein products coded by these genes has proved to be a major challenge. Computational methods that have been used to assign functions to such sequences often result in high levels of misannotations. Nature's strategy of evolving new function provides clues for formulating an accurate predictive scheme for functional annotation. Constraints associated with substrate binding properties and chemistry have been shown to be major determinants of guiding the evolution of new function. In this study, the authors have explored the functional and structural constraints imposed by complex cofactors on the evolution of new functions. Analysis of the large “two dinucleotide binding domains” flavoproteins (tDBDF) superfamily using structural comparisons and other bioinformatics approaches shows how structural requirements associated with cofactor reactivity constrain the mode of protein–protein interactions while providing the major route for evolution of functional diversification. The evolutionary framework established in this work may be generally useful for the analysis of functional divergence in other enzyme superfamilies that use complex cofactors.

Clinical and molecular investigations of Japanese cases of glutaric acidemia type 2

Glutaric acidemia type 2 (GA2) is an autosomal recessive disorder resulting from a deficiency of electron transfer flavoprotein (ETF) or ETF dehydrogenase (ETFDH) that manifests from most severe neonatal to late-onset forms. However, the genetic defect responsible for the disease and clinical severity is not well-characterized. In order to understand the relationship between the phenotype and genetic defect, we investigated the clinical and molecular features of 15 Japanese patients, including 4 previously reported cases. Three patients had the neonatal form and 8 patients had the late-onset form, 1 of whom presented an extremely mild phenotype. Immunoblot analysis showed that either ETFalpha, ETFbeta, or ETFDH was significantly reduced or absent in all patients. However, no specific enzyme deficiency predominated, and there were no associations with the clinical severity. Genetic analyses identified 15 mutations including non-sense, missense, splice site mutations, and small deletions, in ETFA, ETFB and ETFDH genes. Although almost all mutations were unique to Japanese patients and no common mutations were found, some of them appeared to be associated with a specific phenotype. Our results suggest that clinical and mutational spectrums of Japanese GA2 patients are heterogeneous and that genetic diagnoses may help to predict a prognosis and provide more accurate diagnostic information for patients and families with GA2.

Biochemical, spectroscopic, and thermodynamic properties of flavodiiron proteins

The flavodiiron proteins (FDPs), present in Archaea, Bacteria, and some protozoan pathogens (mostly anaerobes or microaerophiles), have been proposed to afford protection to microbes against nitric oxide and/or oxygen (toxic for anaerobes). The structural prototype of this protein family is a homodimer assembled in a "head-to-tail" configuration, with each monomer being composed of two domains: an N-terminal metallo-beta-lactamase module harboring a nonheme diiron center (active site of NO/O(2) reduction) and a C-terminal flavodoxin module, where a flavin mononucleotide moiety is embedded. Several FDPs bear C-terminal extra domains, which influence the composition of the respective electron transfer chains that couple NAD(P)H oxidation to NO/O(2) reduction. Herein are described methodologies employed to successfully produce, isolate, and characterize fully operative recombinant flavodiiron proteins. Spectroscopic techniques, namely absorption (visible and near-ultraviolet) and electron paramagnetic resonance spectroscopies, allowed redox-sensitive spectral fingerprints to be obtained, used further in the functional characterization of isolated flavodiiron proteins. Altogether, these studies on pure proteins contribute to understanding the molecular determinants that govern the in vivo function of the FDPs.

Risk of sudden death and acute life-threatening events in patients with glutaric acidemia type II

Glutaric acidemia type II (GAII) is an inborn error of metabolism caused by defects in electron transport flavoprotein (ETF) or ETF-ubiquinone oxidoreductase (ETF-QO) and typically presents with hypo- or nonketotic hypoglycemia and metabolic acidosis. The most severe forms present in early infancy and are associated with a high mortality rate. The disorder can now be detected by expanded newborn screening using tandem mass spectrometry (MS/MS), providing the opportunity for diagnosis and treatment in asymptomatic infants. We report here three infants who, despite diagnosis and treatment in the neonatal period, experienced either unexpected sudden death or an acute life-threatening event (ALTE) during the first year of life. The possible etiologies of these events and the potential impact of expanded newborn screening on the long-term outcome of GAII are discussed.

Transient multiple acyl-CoA dehydrogenation deficiency in a newborn female caused by maternal riboflavin deficiency

A newborn female presented on the first day of life with clinical and biochemical findings consistent with multiple acyl-CoA dehydrogenase deficiency (MADD). Riboflavin supplementation corrected the biochemical abnormalities 24 h after commencing the vitamin. In vitro acylcarnitine profiling in intact fibroblasts both in normal and riboflavin depleted media showed normal oxidation of fatty acids excluding defects in electron transfer flavoprotein (ETF), or ETF ubiquinone oxidoreductase (ETF:QO), or a genetic abnormality in flavin metabolism. In addition, sequencing of the genes encoding ETF and ETF:QO in the proband did not reveal any pathogenic mutations. Determination of the maternal riboflavin status after delivery showed that the mother was riboflavin deficient. Repeat testing done two years after the infant's birth and while on a normal diet showed that the mother was persistently riboflavin deficient and showed a typical MADD profile on plasma acylcarnitine testing. A possible genetic defect in riboflavin transport of metabolism in the mother is postulated to be the cause of the transient MADD seen in the infant. Sequencing of the SLC16A12, RFK and FLAD1 genes encoding key enzymes in riboflavin transport of metabolism in the mother did not identify any pathogenic mutations. The underlying molecular basis of the mother's defect in riboflavin metabolism remains to be established.

ETFDH mutations as a major cause of riboflavin-responsive multiple acyl-CoA dehydrogenation deficiency

Multiple acyl-CoA dehydrogenation deficiency (MADD) is a disorder of fatty acid, amino acid and choline metabolism that can result from defects in two flavoproteins, electron transfer flavoprotein (ETF) or ETF: ubiquinone oxidoreductase (ETF:QO). Some patients respond to pharmacological doses of riboflavin. It is unknown whether these patients have defects in the flavoproteins themselves or defects in the formation of the cofactor, FAD, from riboflavin. We report 15 patients from 11 pedigrees. All the index cases presented with encephalopathy or muscle weakness or a combination of these symptoms; several had previously suffered cyclical vomiting. Urine organic acid and plasma acyl-carnitine profiles indicated MADD. Clinical and biochemical parameters were either totally or partly corrected after riboflavin treatment. All patients had mutations in the gene for ETF:QO. In one patient, we show that the ETF:QO mutations are associated with a riboflavin-sensitive impairment of ETF:QO activity. This patient also had partial deficiencies of flavin-dependent acyl-CoA dehydrogenases and respiratory chain complexes, most of which were restored to control levels after riboflavin treatment. Low activities of mitochondrial flavoproteins or respiratory chain complexes have been reported previously in two of our patients with ETF:QO mutations. We postulate that riboflavin-responsive MADD may result from defects of ETF:QO combined with general mitochondrial dysfunction. This is the largest collection of riboflavin-responsive MADD patients ever reported, and the first demonstration of the molecular genetic basis for the disorder.

The myopathic form of coenzyme Q10 deficiency is caused by mutations in the electron-transferring-flavoprotein dehydrogenase (ETFDH) gene

Coenzyme Q10 (CoQ10) deficiency is an autosomal recessive disorder with heterogenous phenotypic manifestations and genetic background. We describe seven patients from five independent families with an isolated myopathic phenotype of CoQ10 deficiency. The clinical, histological and biochemical presentation of our patients was very homogenous. All patients presented with exercise intolerance, fatigue, proximal myopathy and high serum CK. Muscle histology showed lipid accumulation and subtle signs of mitochondrial myopathy. Biochemical measurement of muscle homogenates showed severely decreased activities of respiratory chain complexes I and II + III, while complex IV (COX) was moderately decreased. CoQ10 was significantly decreased in the skeletal muscle of all patients. Tandem mass spectrometry detected multiple acyl-CoA deficiency, leading to the analysis of the electron-transferring-flavoprotein dehydrogenase (ETFDH) gene, previously shown to result in another metabolic disorder, glutaric aciduria type II (GAII). All of our patients carried autosomal recessive mutations in ETFDH, suggesting that ETFDH deficiency leads to a secondary CoQ10 deficiency. Our results indicate that the late-onset form of GAII and the myopathic form of CoQ10 deficiency are allelic diseases. Since this condition is treatable, correct diagnosis is of the utmost importance and should be considered both in children and in adults. We suggest to give patients both CoQ10 and riboflavin supplementation, especially for long-term treatment.