Heterogeneous Phenotypes in Lipid Storage Myopathy Due to ETFDH Gene Mutations

Lipid-storage myopathy with glycogen storage disease gene mutations mimicking polymyositis: a case report and review of the literature

A 26-year-old Asian woman with persistent muscle weakness was diagnosed with polymyositis based on biopsy findings at another hospital 11 years ago. However, her symptoms fluctuated repeatedly under treatment with prednisone and immunosuppressive agents, and worsened 2 months prior to the current presentation. A second muscle biopsy suggested metabolic myopathy, and genetic testing revealed a novel c.1074C > T variant in the glycogen synthase 1 gene (GYS1), which is implicated in muscle glycogen storage disease type 0. However, no abnormalities in glycogen deposition were found by biopsy; rather, muscle fibers exhibited large intracellular lipid droplets. Furthermore, muscle strength was greatly restored and circulating levels of creatine kinase indicative of muscle degeneration greatly reduced by vitamin B2 treatment. Therefore, the final diagnosis was lipid storage myopathy.

Diagnostic Challenges in Late Onset Multiple Acyl-CoA Dehydrogenase Deficiency: Clinical, Morphological, and Genetic Aspects

Background

Multiple acyl-CoA dehydrogenase deficiency (MADD) is an autosomal recessive disorder of fatty acid oxidation due to deficiency of the mitochondrial electron transfer chain. The late-onset form is characterized by exercise intolerance, muscle weakness, and lipid storage in myofibers. Most MADD patients greatly benefit from riboflavin supplementation.

Patients and methods

A retrospective study was conducted on patients with a diagnosis of vacuolar myopathy with lipid storage followed in our neuromuscular unit in the last 20 years. We selected 10 unrelated patients with the diagnosis of MADD according to clinical, morphological, and biochemical aspects. Clinical features, blood tests including serum acylcarnitines, EMG, and ENG were revised. Muscle biopsy was performed in all, and one individual underwent also a sural nerve biopsy. Gene sequencing of ETFA, ETFB, and ETFDH was performed as a first-tier genetic analysis followed by next-generation sequencing of an hyperCKemia gene panel in patients with undefined genotypes.

Results

Clinical evaluation at onset in all our patients showed fatigue and muscle weakness; four patients showed difficulties in chewing, three patients complained of dysphagia, two patients had a dropped head, and a patient had an unexpected ataxia with numbness and dysesthesia. Laboratory blood tests revealed a variable increase in serum CK (266–6,500) and LDH levels (500–2,000). Plasma acylcarnitine profile evidenced increased levels of different chains intermediates. EMG was either normal or showed myogenic or neurogenic patterns. NCS demonstrated sensory neuropathy in two patients. Muscle biopsies showed a vacuolar myopathy with a variable increase in lipid content. Nerve biopsy evidenced an axonal degeneration with the loss of myelinated fibers. ETFDH genetic analysis identifies 14 pathogenic variants. Patients were treated with high doses of riboflavin (400 mg/die). All of them showed a rapid muscle strength improvement and normalization of abnormal values in laboratory tests. Neuropathic symptoms did not improve.

Conclusion

Our data confirmed that clinical features in MADD patients are extremely variable in terms of disease onset and symptoms making diagnosis difficult. Laboratory investigations, such as serum acylcarnitine profile and muscle biopsy evaluation, may strongly address to a correct diagnosis. The favorable response to riboflavin supplementation strengthens the importance of an early diagnosis of these disorders among the spectrum of metabolic myopathies.

Mutation spectrum of primary lipid storage myopathies

Background:

Lipid storage myopathies (LSM) constitute an important group of treatable myopathies. Genetic testing is essential for confirming the diagnosis and also helps in explaining phenotypic heterogeneity. The objective of this study was to describe the clinical features and genetic spectrum of LSM seen in a quaternary referral center in India.

Methods:

Eleven cases of suspected LSM underwent clinical, biochemical, histopathological and genetic evaluation. Tandem Mass Spectrometry and clinical exome sequencing with Sanger validation were performed.

Results:

All patients had exertion induced myalgia and either progressive or episodic limb girdle muscle weakness (LGMW). The age of onset ranged 10 to 31 years (mean- 21 ± 6.7y), age at presentation- 14 to 49 years (mean- 26.5 ± 9.5y). Mutations identified: ETFDH = 5, CPT2 = 3, FLAD1 = 1, ACADVL = 1, FLAD1 = 1. Dropped head syndrome was seen in two patients with ETFDH mutations. Bulbar symptoms and Beevor's sign were noted in a patient with FLAD1 variant. Novel variants were identified in seven patients.

Conclusions:

This is the first report on the genetic spectrum of LSM from India. LSM should be considered in patients with exertion induced myalgias, LGMW, cranial nerve involvement or dropped head syndrome. Genetic testing is essential for identification of these treatable disorders.

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.

Role of RNA in Molecular Diagnosis of MADD Patients

The electron-transfer flavoprotein dehydrogenase gene (ETFDH) encodes the ETF-ubiquinone oxidoreductase (ETF-QO) and has been reported to be the major cause of multiple acyl-CoA dehydrogenase deficiency (MADD). In this study, we present the clinical and molecular diagnostic challenges, at the DNA and RNA levels, involved in establishing the genotype of four MADD patients with novel ETFDH variants: a missense variant, two deep intronic variants and a gross deletion. RNA sequencing allowed the identification of the second causative allele in all studied patients. Simultaneous DNA and RNA investigation can increase the number of MADD patients that can be confirmed following the suggestive data results of an expanded newborn screening program. In clinical practice, accurate identification of pathogenic mutations is fundamental, particularly with regard to diagnostic, prognostic, therapeutic and ethical issues. Our study highlights the importance of RNA studies for a definitive molecular diagnosis of MADD patients, expands the background of ETFDH mutations and will be important in providing an accurate genetic counseling and a prenatal diagnosis for the affected families.

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.

Inherited Neuromuscular Disorders: Which Role for Serum Biomarkers?

Inherited neuromuscular disorders (INMD) are a heterogeneous group of rare diseases that involve muscles, motor neurons, peripheral nerves or the neuromuscular junction. Several different lab abnormalities have been linked to INMD: sometimes they are typical of the disorder, but they usually appear to be less specific. Sometimes serum biomarkers can point out abnormalities in presymtomatic or otherwise asymptomatic patients (e.g., carriers). More often a biomarker of INMD is evaluated by multiple clinicians other than expert in NMD before the diagnosis, because of the multisystemic involvement in INMD. The authors performed a literature search on biomarkers in inherited neuromuscular disorders to provide a practical approach to the diagnosis and the correct management of INMD. A considerable number of biomarkers have been reported that support the diagnosis of INMD, but the role of an expert clinician is crucial. Hence, the complete knowledge of such abnormalities can accelerate the diagnostic workup supporting the referral to specialists in neuromuscular disorders.

Hepatic Presentation of Late-Onset Multiple Acyl-CoA Dehydrogenase Deficiency (MADD): Case Report and Systematic Review

Diagnosis of pediatric steatohepatitis is a challenging issue due to a vast number of established and novel causes. Here, we report a child with Multiple Acyl-CoA Dehydrogenase Deficiency (MADD) presenting with an underrated muscle weakness, exercise intolerance and an atypically severe steatotic liver involvement. A systematic literature review of liver involvement in MADD was performed as well. Our patient is a 11-year-old otherwise healthy, non-obese, male child admitted for some weakness/asthenia, vomiting and recurrent severe hypertransaminasemia (aspartate and alanine aminotransferases up to ×20 times upper limit of normal). Hepatic ultrasound showed a bright liver. MRI detected mild lipid storage of thighs muscles. A liver biopsy showed a micro-macrovacuolar steatohepatitis with minimal fibrosis. Main causes of hypertransaminasemia were ruled out. Serum aminoacids (increased proline), acylcarnitines (increased C4-C18) and a large excretion of urinary glutaric acid, ethylmalonic, butyric, isobutyric, 2-methyl-butyric and isovaleric acids suggested a diagnosis of MADD. Serum acylcarnitines and urinary organic acids fluctuated overtime paralleling serum transaminases during periods of illness/catabolic stress, confirming their recurrent nature. Genetic testing confirmed the diagnosis [homozygous c.1658A > G (p.Tyr553Cys) in exon 12 of the ETFDH gene]. Lipid-restricted diet and riboflavin treatment rapidly ameliorated symptoms, hepatic ultrasonography/enzymes, and metabolic profiles. Literature review (37 retrieved eligible studies, 283 patients) showed that liver is an extramuscular organ rarely involved in late-onset MADD (70 patients), and that amongst 45 patients who had fatty liver only nine had severe presentation. Conclusion: MADD is a disorder with a clinically heterogeneous phenotype. Our study suggests that MADD warrants consideration in the work-up of obesity-unrelated severe steatohepatitis.

Clinical characteristics and gene mutation analysis of an adult patient with ETFDH‑related multiple acyl‑CoA dehydrogenase deficiency

Multiple acyl‑CoA dehydrogenase deficiency (MADD) is a rare autosomal recessive disorder of fatty acid metabolism caused by defects in electron transfer flavoprotein (ETF) or electron transfer flavoprotein dehydrogenase (ETFDH). These defects are mainly classified into the neonatal and late‑onset types, based on their clinical manifestations. ETFDH gene mutations are generally considered to be associated with the late‑onset type. The present study reported an adult woman with late‑onset MADD accompanied with biochemical and muscle biopsy findings indicating metabolic disorders. Gene sequencing analysis showed that the c.1514T>C homozygous mutation in the region of the 12th exon of the ETFDH gene, which led to the amino acid substitution p.I505T (isoleucine > threonine), resulting in defective ETFDH protein function. The results of family verification revealed that the homozygous mutation originated from her parents. The female patient was treated with a large dose of vitamin B2, L‑carnitine and coenzyme Q10, and the symptoms were significantly relieved. The c.1514T>C mutation in the ETFDH gene, was considered as a novel pathogenic mutation that had not been previously reported. Therefore, it was hypothesized that this mutation was responsible for the clinical characteristics of the adult female patient. Overall, this novel mutation could expand the spectrum of the ETFDH gene mutation and provide the basis for the etiological and prenatal diagnosis of 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.

A novel electron transfer flavoprotein dehydrogenase (ETFDH) gene mutation identified in a newborn with glutaric acidemia type II: a case report of a Chinese family

Background

Glutaric acidemia type II (GA II) or multiple acyl-CoA dehydrogenase deficiency (MADD, OMIM 231680) 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, electron transfer flavoprotein β-subunit, ETFB and electron transfer flavoprotein dehydrogenase, ETFDH. Currently, few studies have reported genetic profiling of neonatal-onset GA II. This study aimed to identify the genetic mutations in a Chinese family with GA II.

Case presentation

We reported a case of GA II with purulent meningitis and septicemia and identified a novel ETFDH gene mutation in a female infant. The patient developed an episode of hypoglycemia and hypotonicity on the postnatal first day. Laboratory investigations revealed elevations of multiple acylcarnitines indicating glutaric acidemia type II in newborn screening analysis. Urinary organic acids were evaluated for the confirmation and revealed a high glutaric acid excretion. Genetic analysis revealed two mutations in the ETFDH gene (c.623_626 del / c. 1399G > C), which were considered to be the etiology for the disease. The novel mutation c.623_626 del was identified in the proband infant and her father, her mother was carriers of the mutation c.1399G > C.

Conclusions

A novel variant (c.623_626 del) and a previously reported missense (c.1399G > C) in the ETFDH gene have been identified in the family. The two variants of ETFDH gene identified probably underlie the pathogenesis of Glutaric acidemia type II in this family, and also enlarge ETFDH genotype-phenotype correlations spectrum.

Thirty years of translational research in Mobility Medicine: Collection of abstracts of the 2020 Padua Muscle Days

More than half a century of skeletal muscle research is continuing at Padua University (Italy) under the auspices of the Interdepartmental Research Centre of Myology (CIR-Myo), the European Journal of Translational Myology (EJTM) and recently also with the support of the A&CM-C Foundation for Translational Myology, Padova, Italy. The Volume 30(1), 2020 of the EJTM opens with the collection of abstracts for the conference "2020 Padua Muscle Days: Mobility Medicine 30 years of Translational Research". This is an international conference that will be held between March 18-21, 2020 in Euganei Hills and Padova in Italy. The abstracts are excellent examples of translational research and of the multidimensional approaches that are needed to classify and manage (in both the acute and chronic phases) diseases of Mobility that span from neurologic, metabolic and traumatic syndromes to the biological process of aging. One of the typical aim of Physical Medicine and Rehabilitation is indeed to reduce pain and increase mobility enough to enable impaired persons to walk freely, garden, and drive again. The excellent contents of this Collection of Abstracts reflect the high scientific caliber of researchers and clinicians who are eager to present their results at the PaduaMuscleDays. A series of EJTM Communications will also add to this preliminary evidence.

Correlation between ETFDH mutations and dysregulation of serum myomiRs in MADD patients

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare fatty acids oxidation disorder which is often associated with deficiency of electron transfer flavoprotein dehydrogenase (ETFDH). In this study we reported clinical features and evaluation of expression profile of circulating muscle-specific miRNAs (myomiRs) in two MADD patients carrying different ETFDH gene mutations. Patient 1 was a compound heterozygote for two missense mutations. She showed a late onset MADD clinical phenotype and a significant increase of serum myomiRs. Patient 2, carrying a missense and a frameshift mutation, displayed early onset symptoms and a slight increase of some serum myomiRs.

Skin damage in a patient with lipid storage myopathy with a novel ETFDH mutation responsive to riboflavin

Background: Recessive mutations in ETFDH gene have been associated with Multiple Acyl-CoA dehydrogenase deficiency (MADD). The late-onset MADD is often muscle involved, presenting with lipid storage myopathy (LSM). The symptoms of LSM were heterogeneous and definite diagnosis of this disease depends on the pathology and gene test.Methods: Neurological examination, muscle biopsy, and MRI examinations were performed in a patient with a novel missense ETFDH mutation.Results: We describe a patient with lipid storage myopathy complicated with skin damage. In addition, the next generation revealed a novel missense mutation (c.970G > T, p.Val324Leu) in exon 8, which was predicted to be a disease-causing mutation by Mutation-taster, and destroy the function of the protein by Sift.Conclusion: These findings expand the known mutational spectrum of ETFDH and phenotype of MADD.

Late-onset multiple acyl-CoA dehydrogenase deficiency with cardiac syncope: A case report

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD) is an uncommon autosomal recessive disorder of mitochondrial fatty acid beta-oxidation. Syncope is a transient loss of consciousness due to acute global cerebral hypoperfusion. Late-onset MADD with syncope has not been reported previously.

CASE SUMMARY

We report a 17-year-old girl with exercise intolerance and muscle weakness. She felt palpitation and shortness of breath after short bouts of exercise. She also suffered from a transient loss of consciousness many times. Muscle biopsy showed lipid storage. Genetic mutation analysis indicated a compound heterozygous mutation c.250G > A (p.A84T) and c.872T > G (p.V291G) in the ETFDH gene. The results of Holter electrocardiogram monitoring showed supraventricular tachycardia when the patient experienced a loss of consciousness. After treatment with riboflavin and carnitine, muscle weakness and palpitation symptoms improved rapidly. No loss of consciousness occurred, and the Holter electrocardiogram monitoring was normal.

CONCLUSION

Late-onset MADD with supraventricular tachycardia can cause cardiac syncope. Carnitine and riboflavin supplement were beneficial for treating the late-onset MADD with cardiac syncope. Attention should be paid to the prevention of cardiac syncope when diagnosing late-onset MADD.

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.

Two novel ETFDH mutations in a patient with lipid storage myopathy

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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.

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.

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.

Lipophagy in nonliver tissues and some related diseases: Pathogenic and therapeutic implications

Lipid autophagy (lipophagy) is defined as a selective autophagy process in which some intracellular lipid droplets are selectively degraded by autophagic lysosomes pathway. The occurrence of lipophagy was first discovered in liver tissues. Additionally, abundant evidence indicated that the occurrence of hepatic lipophagy has been implicated in many liver diseases including fatty liver diseases, nonalcoholic fatty liver diseases, liver fibrosis, and liver cirrhosis. However, recent studies suggested that hepatic lipophagy occurs not only in liver tissue but also in other nonliver tissues and cells. Furthermore, the occurrence of lipophagy plays a crucial role in nonliver tissues and some related diseases. For instance, lipophagy relieves insulin resistance in adipose tissue from obesity patient with type 2 diabetes. Additionally, lipophagy has the ability to remit neurodegenerative diseases by reducing activity-dependent neurodegeneration in nervous tissue. Lipophagy decreases muscle lipid accumulation and accordingly improves lipid storage myopathy in muscle tissue. Moreover, lipophagy alleviates the malignancy and metastasis of cancer in clear renal cell carcinoma tissue. Lipophagy is also involved in other processes, such as spermatogenesis, osteoblastogenesis, and mucosal ulceration. In conclusion, targeting lipophagy may be a critical regulator and a new therapeutic strategy for nonliver tissues and some related diseases.

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.

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.

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.

Mitochondrial β-oxidation of saturated fatty acids in humans

Mitochondrial β-oxidation of fatty acids generates acetyl-coA, NADH and FADH₂. Acyl-coA synthetases catalyze the binding of fatty acids to coenzyme A to form fatty acyl-coA thioesters, the first step in the intracellular metabolism of fatty acids. l-carnitine system facilitates the transport of fatty acyl-coA esters across the mitochondrial membrane. Carnitine palmitoyltransferase-1 transfers acyl groups from coenzyme A to l-carnitine, forming acyl-carnitine esters at the outer mitochondrial membrane. Carnitine acyl-carnitine translocase exchanges acyl-carnitine esters that enter the mitochondria, by free l-carnitine. Carnitine palmitoyltransferase-2 converts acyl-carnitine esters back to acyl-coA esters at the inner mitochondrial membrane. The β-oxidation pathway of fatty acyl-coA esters includes four reactions. Fatty acyl-coA dehydrogenases catalyze the introduction of a double bond at the C2 position, producing 2-enoyl-coA esters and reducing equivalents that are transferred to the respiratory chain via electron transferring flavoprotein. Enoyl-coA hydratase catalyzes the hydration of the double bond to generate a 3-l-hydroxyacyl-coA derivative. 3-l-hydroxyacyl-coA dehydrogenase catalyzes the formation of a 3-ketoacyl-coA intermediate. Finally, 3-ketoacyl-coA thiolase catalyzes the cleavage of the chain, generating acetyl-coA and a fatty acyl-coA ester two carbons shorter. Mitochondrial trifunctional protein catalyzes the three last steps in the β-oxidation of long-chain and medium-chain fatty acyl-coA esters while individual enzymes catalyze the β-oxidation of short-chain fatty acyl-coA esters. Clinical phenotype of fatty acid oxidation disorders usually includes hypoketotic hypoglycemia triggered by fasting or infections, skeletal muscle weakness, cardiomyopathy, hepatopathy, and neurological manifestations. Accumulation of non-oxidized fatty acids promotes their conjugation with glycine and l-carnitine and alternate ways of oxidation, such as ω-oxidation.