Biochemical, clinical and molecular findings in LCHAD and general mitochondrial trifunctional protein deficiency

New Acylcarnitine Ratio as a Reliable Indicator of Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiencies are rare fatal disorders of fatty acid β-oxidation with no apparent genotype-phenotype correlation. The measurement of acylcarnitines by MS/MS is a current diagnostic workup in these disorders. Nevertheless, false-positive and false-negative results have been reported, highlighting a necessity for more sensitive and specific biomarkers. This study included 54 patients with LCHAD/MTP deficiency that has been confirmed by biochemical and molecular methods. The analysis of acylcarnitines in dried blood spots was performed using ESI-MS/MS. The established "HADHA ratio" = (C16OH + C18OH + C18:1OH)/C0 was significantly elevated in all 54 affected individuals in comparison to the control group. Apart from 54 LCHAD deficiency patients, the "HADHA ratio" was calculated in 19 patients with very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. As VLCAD-deficient patients did not show increased "HADHA ratio", the results emphasized the high specificity of this new ratio. Therefore, the "HADHA ratio" was shown to be instrumental in improving the overall performance of MS/MS-based analysis of acylcarnitine levels in the diagnostics of LCHAD/MTP deficiencies. The ratio was demonstrated to increase the sensitivity and specificity of this method and reduce the chances of false-negative results.

Strategy for genetic analysis in hereditary neuropathy

Inherited neuropathies are a heterogeneous group of slowly progressive disorders affecting either motor, sensory, and/or autonomic nerves. Peripheral neuropathy may be the major component of a disease such as Charcot-Marie-Tooth disease or a feature of a more complex multisystemic disease involving the central nervous system and other organs. The goal of this review is to provide the clinical clues orientating the genetic diagnosis in a patient with inherited peripheral neuropathy. This review focuses on primary inherited neuropathies, amyloidosis, inherited metabolic diseases, while detailing clinical, neurophysiological and potential treatment of these diseases.

Neonatal Long-Chain 3-Ketoacyl-CoA Thiolase deficiency: Clinical-biochemical phenotype, sodium-D,L-3-hydroxybutyrate treatment experience and cardiac evaluation using speckle echocardiography

Isolated long-chain 3-keto-acyl CoA thiolase (LCKAT) deficiency is a rare long-chain fatty acid oxidation disorder caused by mutations in HADHB. LCKAT is part of a multi-enzyme complex called the mitochondrial trifunctional protein (MTP) which catalyzes the last three steps in the long-chain fatty acid oxidation. Until now, only three cases of isolated LCKAT deficiency have been described. All patients developed a severe cardiomyopathy and died before the age of 7 weeks. Here, we describe a newborn with isolated LCKAT deficiency, presenting with neonatal-onset cardiomyopathy, rhabdomyolysis, hypoglycemia and lactic acidosis. Bi-allelic 185G > A (p.Arg62His) and c1292T > C (p.Phe431Ser) mutations were found in HADHB. Enzymatic analysis in both lymphocytes and cultured fibroblasts revealed LCKAT deficiency with a normal long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD, also part of MTP) enzyme activity. Clinically, the patient showed recurrent cardiomyopathy, which was monitored by speckle tracking echocardiography. Subsequent treatment with special low-fat formula, low in long chain triglycerides (LCT) and supplemented with medium chain triglycerides (MCT) and ketone body therapy in (sodium-D,L-3-hydroxybutyrate) was well tolerated and resulted in improved carnitine profiles and cardiac function. Resveratrol, a natural polyphenol that has been shown to increase fatty acid oxidation, was also considered as a potential treatment option but showed no in vitro benefits in the patient's fibroblasts. Even though our patient deceased at the age of 13 months, early diagnosis and prompt initiation of dietary management with addition of sodium-D,L-3-hydroxybutyrate may have contributed to improved cardiac function and a much longer survival when compared to the previously reported cases of isolated LCKAT-deficiency.

Shedding light on the phenotypic–genotypic correlation of rare treatable and potentially treatable pediatric movement disorders

Background

Advances in genetic science have led to the identification of many rare treatable pediatric movements disorders (MDs). We explored the phenotypic–genotypic spectrum of pediatric patients presenting with MDs. By this, we aimed at raising awareness about such rare disorders, especially in our region. Over the past 3 years, we reviewed the demographic data, clinical profile, molecular genetics and other diagnostic workups of pediatric patients presenting with MDs.

Results

Twelve patients were identified; however, only six patients were genetically confirmed. The phenomenology of MDs ranged from paroxysmal kinesigenic choreoathetosis (1 patient), exercise-induced dyskinesia (2 patients), ataxia (2 patients) and dystonia (2 patients). Whole-exome sequencing in addition to the functional studies for some patients revealed a specific genetic diagnosis being responsible for their MDs. The genetic diagnosis of our patients included infantile convulsions and paroxysmal choreoathetosis syndrome and episodic ataxia due to “pathogenic homozygous mutation of PRRT2 gene,” glucose transporter type 1 deficiency-exercise induced dyskinesia due to “De Novo pathogenic heterozygous missense mutation of exon 4 of SLC2A1 gene,” aromatic L amino acid decarboxylase deficiency due to “pathogenic homozygous mutation of the DDC gene,” myopathy with extrapyramidal signs due to “likely pathogenic homozygous mutations of the MICU1 gene,” mitochondrial trifunctional protein deficiency due to “homozygous variant of uncertain significance (VUS) of HADHB gene” and glutaric aciduria II with serine deficiency due to “homozygous VUS for both ETFDH and PHGDH genes.” After receiving the treatment as per recognized treatment protocols, two patients showed complete resolution of symptoms and the rest showed variable responses.

Conclusion

Identifying the genetic etiology of our patients guided us to provide either disease-specific treatment or redirected our management plan. Hence, highlighting the value of molecular genetic analysis to avoid the diagnostic odyssey and identify treatable MDs.

Mitochondrial Dysfunction and Acute Fatty Liver of Pregnancy

The liver is one of the richest organs in mitochondria, serving as a hub for key metabolic pathways such as β-oxidation, the tricarboxylic acid (TCA) cycle, ketogenesis, respiratory activity, and adenosine triphosphate (ATP) synthesis, all of which provide metabolic energy for the entire body. Mitochondrial dysfunction has been linked to subcellular organelle dysfunction in liver diseases, particularly fatty liver disease. Acute fatty liver of pregnancy (AFLP) is a life-threatening liver disorder unique to pregnancy, which can result in serious maternal and fetal complications, including death. Pregnant mothers with this disease require early detection, prompt delivery, and supportive maternal care. AFLP was considered a mysterious illness and though its pathogenesis has not been fully elucidated, molecular research over the past two decades has linked AFLP to mitochondrial dysfunction and defects in fetal fatty-acid oxidation (FAO). Due to deficient placental and fetal FAO, harmful 3-hydroxy fatty acid metabolites accumulate in the maternal circulation, causing oxidative stress and microvesicular fatty infiltration of the liver, resulting in AFLP. In this review, we provide an overview of AFLP and mitochondrial FAO followed by discussion of how altered mitochondrial function plays an important role in the pathogenesis of AFLP.

Modeling Rare Human Disorders in Mice: The Finnish Disease Heritage

The modification of genes in animal models has evidently and comprehensively improved our knowledge on proteins and signaling pathways in human physiology and pathology. In this review, we discuss almost 40 monogenic rare diseases that are enriched in the Finnish population and defined as the Finnish disease heritage (FDH). We will highlight how gene-modified mouse models have greatly facilitated the understanding of the pathological manifestations of these diseases and how some of the diseases still lack proper models. We urge the establishment of subsequent international consortiums to cooperatively plan and carry out future human disease modeling strategies. Detailed information on disease mechanisms brings along broader understanding of the molecular pathways they act along both parallel and transverse to the proteins affected in rare diseases, therefore also aiding understanding of common disease pathologies.

The spectrum of peripheral neuropathy in disorders of the mitochondrial trifunctional protein

Peripheral neuropathy is a known irreversible long-term complication of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) and mitochondrial trifunctional protein deficiency (MTPD), two inherited disorders of mitochondrial long-chain fatty acid oxidation. The underlying pathophysiology of neuropathy is still not fully understood. We report electrophysiological studies and neurological findings in a series of 8 LCHAD-deficient and 11 MTP-deficient patients. The median age at time of the study was 8.0 years (0.5-25 years). The overall prevalence of neuropathy was 58% with neuropathic symptoms being slightly more common in MTPD compared to LCHADD (70% vs 50%, respectively). Onset of neuropathy was significantly earlier in MTPD patients compared to LCHADD patients (median age at onset 4.7 vs 15.3 years, respectively, P = .047). In four patients, isolated peripheral neuropathy was the first and only presenting symptom, and in all four the diagnosis was missed by newborn screening. About half of the patients (45.5%) had a sensorimotor neuropathy, while 27.3% showed a pure motor form and another 27.3% an isolated sensory form. Despite early diagnosis by newborn screening and early initiation of therapy, peripheral neuropathy cannot be prevented in all patients with LCHADD/MTPD and has severe impact on the life of affected patients. Electrophysiology classifies LCHADD/MTPD neuropathy as axonal with secondary demyelination. A novel observation is that in patients with acute, fulminant onset of neuropathy, symptoms can be partly reversible. Further studies are needed to elucidate the underlying pathophysiology of axonal damage and possible therapeutic targets.

MTP deficiency caused by HADHB mutations: Pathophysiology and clinical manifestations

Mutations in the HADHB gene lead to Mitochondrial Trifunctional Protein (MTP) deficiency. MTP deficiency is a rare autosomal recessive disorder affecting long-chain fatty acid oxidation. Patients affected by MTP deficiency are unable to metabolize long-chain fatty-acids and suffer a variety of symptoms exacerbated during fasting. The three phenotypes associated with complete MTP deficiency are an early-onset cardiomyopathy and early death, an intermediate form with recurrent hypoketotic hypoglycemia and a sensorimotor neuropathy with episodic rhabdomyolysis with small amount of residual enzyme activities. This review aims to discuss the pathophysiological mechanisms and clinical manifestations of each phenotype, which appears different and linked to HADHB expression levels. Notably, the pathophysiology of the sensorimotor neuropathy is relatively unknown and we provide a hypothesis on the qualitative aspect of the role of acylcarnitine buildup in Schwann cells in MTP deficiency patients. We propose that acylcarnitine may exit the Schwann cell and alter membrane properties of nearby axons leading to axonal degeneration based on recent findings in different metabolic disorders.

Expanding the genotype-phenotype correlation of childhood sensory polyneuropathy of genetic origin

Pure sensory polyneuropathy of genetic origin is rare in childhood and hence important to document the clinical and genetic etiologies from single or multi-center studies. This study focuses on a retrospective chart-review of neurological examinations and genetic and electrodiagnostic data of confirmed sensory polyneuropathy in subjects at a tertiary-care Children's Hospital from 2013 to 2019. Twenty subjects were identified and included. Neurological examination and electrodiagnostic testing showed gait-difficulties, absent tendon reflexes, decreased joint-position, positive Romberg's test and large fiber sensory polyneuropathy on sensory nerve conduction studies in all patients associated with lower-extremity spasticity (6), cardiac abnormalities or cardiomyopathy (5), developmental delay (4), scoliosis (3), epilepsy (3) and hearing-difficulties (2). Confirmation of genetic diagnosis in correlation with clinical presentation was obtained in all cases (COX20 n = 2, HADHA n = 2, POLG n = 1, FXN n = 4, ATXN2 n = 3, ATM n = 3, GAN n = 2, SPG7 n = 1, ZFYVE26 n = 1, FH n = 1). Our single-center study shows genetic sensory polyneuropathies associated with progressive neurodegenerative disorders such as mitochondrial ataxia, Friedreich ataxia, spinocerebellar ataxia type 2, ataxia telangiectasia, spastic paraplegia, giant axonal neuropathy, and fumarate hydratase deficiency. We also present our cohort data in light of clinical features reported for each gene-specific disease subtype in the literature and highlight the importance of genetic testing in the relevant clinical context of electrophysiological findings of peripheral sensory polyneuropathy.

Evidence that Oxidative Disbalance and Mitochondrial Dysfunction are Involved in the Pathophysiology of Fatty Acid Oxidation Disorders

Mitochondrial fatty acid β-oxidation disorders (FAODs) are a group of about 20 diseases which are caused by specific mutations in genes that codify proteins or enzymes involved in the fatty acid transport and mitochondrial β-oxidation. As a consequence of these inherited metabolic defects, fatty acids can not be used as an appropriate energetic source during special conditions, such as prolonged fasting, exercise or other catabolic states. Therefore, patients usually present hepatopathy, cardiomyopathy, severe skeletal myopathy and neuropathy, besides biochemical features like hypoketotic hypoglycemia, metabolic acidosis, hypotony and hyperammonemia. This set of symptoms seems to be related not only with the energy deficiency, but also with toxic effects provoked by fatty acids and carnitine derivatives accumulated in the tissues of the patients. The understanding of the mechanisms by which these metabolites provoke tissue injury in FAODs is crucial for the developmental of novel therapeutic strategies that promote increased life expectancy, as well as improved life quality for patients. In this sense, the objective of this review is to present evidence from the scientific literature on the role of oxidative damage and mitochondrial dysfunction in the pathogenesis of the most prevalent FAODs: medium-chain acyl-CoA dehydrogenase (MCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies. It is expected that the findings presented in this review, obtained from both animal model and patients studies, may contribute to a better comprehension of the pathophysiology of these diseases.

Sensory neuronopathy as a major clinical feature of mitochondrial trifunctional protein deficiency in adults

INTRODUCTION

Mitochondrial trifunctional protein deficiency (MTPD) is a long-chain fatty acid oxidation disorder characterized by co-existence of rhabdomyolysis episodes and peripheral neuropathy. Two phenotypes are described: generalized mitochondrial trifunctional protein deficiency (gMTPD) and isolated long-chain-3-hydroxyacyl-CoA dehydrogenase deficiency (iLCHADD) that is always associated with the c.1528G>C mutation. Peripheral neuropathy of MTPD is commonly described in children as axonal, length-dependent and sensorimotor.

OBJECTIVES

To report clinical and electrophysiological features of four independent adult MTPD patients with peripheral neuropathy.

RESULTS

Onset of the disease was characterized in all patients by rhabdomyolysis episodes occurring during childhood preceded by severe hypoglycemic episodes in three patients. Peripheral nerve involvement manifesting as sensory ataxia appeared later, during adolescence or adulthood. In all cases, electroneuromyogram showed no length-dependent sensory potentials decrease characteristic of sensory neuronopathy ("ganglionopathy"). All patients harbored at least one c.1528G>C mutation.

DISCUSSION

We describe MTPD as a newly hereditary etiology of sensory neuronopathy in adults, specifically in patients with c.1528G>C mutation. MTPD should be screened for by performing plasma acylcarnitines in patients with chronic sensory neuronopathy and additional suggestive features such as exercise intolerance or retinopathy.

Correlation of gene expression and clinical parameters identifies a set of genes reflecting LV systolic dysfunction and morphological alterations

To gain new insights into the complex pathophysiology of dilated cardiomyopathy (DCM) we performed a quantitative approach to identify genes with expression patterns that linearly correlate with parameters of cardiac morphology (left ventricular end-diastolic diameter indexed by body surface are (LVEDDI), systolic function [LV ejection fraction (LVEF)], and serum levels of cardiac peptide hormone NH2-terminal probrain natriuretic peptide (NT-proBNP) in human endomyocardial biopsies of 47 DCM patients and eight individuals with normal LVEF. A set of genes was identified as common heart failure markers characterized by correlation of their expression with cardiac morphology, systolic function, and NT-proBNP. Among them are already known genes encoding e.g., the natriuretic peptide hormones NPPA and NPPB and its converting enzyme corin, but also potential new heart failure markers like EP300 antisense RNA1 and dimethylarginine dimethylaminohydrolase 1 (DDAH1) along with other genes with so far unknown relation to heart function. In contrast, the expression of other genes including the Ca2+ flux regulating genes phospholamban (PLN), sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA), and extracellular matrix proteins showed significant correlation with LVEF and LVEDDI only. Those genes seem to reflect more specifically pathological alterations of systolic function and morphology in DCM hearts.

Lipid Myopathies

Disorders of lipid metabolism affect several tissues, including skeletal and cardiac muscle tissues. Lipid myopathies (LM) are rare multi-systemic diseases, which most often are due to genetic defects. Clinically, LM can have acute or chronic clinical presentation. Disease onset can occur in all ages, from early stages of life to late-adult onset, showing with a wide spectrum of clinical symptoms. Muscular involvement can be fluctuant or stable and can manifest as fatigue, exercise intolerance and muscular weakness. Muscular atrophy is rarely present. Acute muscular exacerbations, resulting in rhabdomyolysis crisis are triggered by several factors. Several classifications of lipid myopathies have been proposed, based on clinical involvement, biochemical defect or histopathological findings. Herein, we propose a full revision of all the main clinical entities of lipid metabolism disorders with a muscle involvement, also including some those disorders of fatty acid oxidation (FAO) with muscular symptoms not included among previous lipid myopathies classifications.

Role of 3-Hydroxy Fatty Acid-Induced Hepatic Lipotoxicity in Acute Fatty Liver of Pregnancy

Acute fatty liver of pregnancy (AFLP), a catastrophic illness for both the mother and the unborn offspring, develops in the last trimester of pregnancy with significant maternal and perinatal mortality. AFLP is also recognized as an obstetric and medical emergency. Maternal AFLP is highly associated with a fetal homozygous mutation (1528G>C) in the gene that encodes for mitochondrial long-chain hydroxy acyl-CoA dehydrogenase (LCHAD). The mutation in LCHAD results in the accumulation of 3-hydroxy fatty acids, such as 3-hydroxy myristic acid, 3-hydroxy palmitic acid and 3-hydroxy dicarboxylic acid in the placenta, which are then shunted to the maternal circulation leading to the development of acute liver injury observed in patients with AFLP. In this review, we will discuss the mechanistic role of increased 3-hydroxy fatty acid in causing lipotoxicity to the liver and in inducing oxidative stress, mitochondrial dysfunction and hepatocyte lipoapoptosis. Further, we also review the role of 3-hydroxy fatty acids in causing placental damage, pancreatic islet β-cell glucolipotoxicity, brain damage, and retinal epithelial cells lipoapoptosis in patients with LCHAD deficiency.

Mice with an Oncogenic HRAS Mutation are Resistant to High-Fat Diet-Induced Obesity and Exhibit Impaired Hepatic Energy Homeostasis

Costello syndrome is a “RASopathy” that is characterized by growth retardation, dysmorphic facial appearance, hypertrophic cardiomyopathy and tumor predisposition. > 80% of patients with Costello syndrome harbor a heterozygous germline G12S mutation in HRAS. Altered metabolic regulation has been suspected because patients with Costello syndrome exhibit hypoketotic hypoglycemia and increased resting energy expenditure, and their growth is severely retarded. To examine the mechanisms of energy reprogramming by HRAS activation in vivo, we generated knock-in mice expressing a heterozygous Hras G12S mutation (Hras^G12S/+ mice) as a mouse model of Costello syndrome. On a high-fat diet, Hras^G12S/+ mice developed a lean phenotype with microvesicular hepatic steatosis, resulting in early death compared with wild-type mice. Under starvation conditions, hypoketosis and elevated blood levels of long-chain fatty acylcarnitines were observed, suggesting impaired mitochondrial fatty acid oxidation. Our findings suggest that the oncogenic Hras mutation modulates energy homeostasis in vivo.

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Mice expressing Hras G12S (Hras^G12S/+) showed Costello syndrome-like phenotypes, including craniofacial and cardiac defects.

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Hras^G12S/+ mice are resistant to high-fat diet (HFD)-induced obesity, showing microvesicular hepatic steatosis.

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Upon fasting, HFD-fed Hras^G12S/+ mice show abnormal hepatic fatty acid oxidation, hypoketosis and early hypoglycemia.

Costello syndrome is a congenital anomaly syndrome, which is caused by germline mutations in HRAS oncogene. Altered metabolic regulation has been suspected because patients with Costello syndrome exhibit hypoketotic hypoglycemia and increased resting energy expenditure, and growth retardation. Here, we generated a mouse model for Costello syndrome expressing a Hras G12S mutation, which showed craniofacial and heart abnormalities. On a high-fat diet, mutant mice exhibited a lean phenotype with poor weight gain and microvesicular hepatic steatosis. Under starvation conditions, impaired mitochondrial fatty acid oxidation has been observed. These results suggest that oncogenic RAS signaling in mice modulates energy homeostasis in vivo.

Pharmacological inhibition of carnitine palmitoyltransferase 1 restores mitochondrial oxidative phosphorylation in human trifunctional protein deficient fibroblasts

BACKGROUND

Mitochondrial Trifunctional Protein deficiency (TFPD) is a severe genetic disease characterized by altered energy metabolism and accumulation of long-chain (LC) acylcarnitines in blood and tissues. This accumulation could impair the mitochondrial oxidative phosphorylation (OxPhos), contributing to the non-optimal outcome despite conventional diet therapy with medium-chain triglycerides (MCT).

METHOD

Acylcarnitine and OxPhos parameters were measured in TFPD-fibroblasts obtained from 8 children and cultured in medium mimicking fasting (LCFA) or conventional treatment (MCT), with or without Etomoxir (ETX) an inhibitor of carnitine palmitoyltransferase 1 (CPT1) activity, and were compared to results obtained with fibroblasts from 5 healthy-control children. The effects of various acylcarnitines were also tested on control fibroblasts.

RESULTS

In the LCFA-condition, TFPD-fibroblasts demonstrated a large accumulation of LC-acylcarnitines associated with decreased O₂-consumption (63±3% of control, P<0.001) and ATP production (67±5%, P<0.001) without modification of coupling efficiency. A dose-dependent decrease in O₂-consumption was reproduced in control fibroblasts by addition of increasing dose of LC-acylcarnitines, while it was almost preserved with MC-acylcarnitines. The MCT-condition reduced LC-acylcarnitine accumulation and partially improved O₂-consumption (80±3%, P<0.01) in TFPD-fibroblasts. The addition of ETX in both LCFA- and MCT-conditions normalized acylcarnitine profiles and restored O₂-consumption and ATP production at the same levels than control.

CONCLUSION

Accumulation of LC-acylcarnitines plays a major role in the pathophysiology of TFPD, reducing OxPhos capacities. These deleterious effects could be partially prevented by MCT-therapy and totally corrected by ETX. Inhibition of CPT1 may be view as a new therapeutic target for patients with a severe form of TFPD.

Disturbance of mitochondrial functions provoked by the major long-chain 3-hydroxylated fatty acids accumulating in MTP and LCHAD deficiencies in skeletal muscle

The pathogenesis of the muscular symptoms and recurrent rhabdomyolysis that are commonly manifested in patients with mitochondrial trifunctional protein (MTP) and long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiencies is still unknown. In this study we investigated the effects of the major long-chain monocarboxylic 3-hydroxylated fatty acids (LCHFA) accumulating in these disorders, namely 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, on important mitochondrial functions in rat skeletal muscle mitochondria. 3HTA and 3HPA markedly increased resting (state 4) and decreased ADP-stimulated (state 3) and CCCP-stimulated (uncoupled) respiration. 3HPA provoked similar effects in permeabilized skeletal muscle fibers, validating the results obtained in purified mitochondria. Furthermore, 3HTA and 3HPA markedly diminished mitochondrial membrane potential, NAD(P)H content and Ca(2+) retention capacity in Ca(2+)-loaded mitochondria. Mitochondrial permeability transition (mPT) induction probably underlie these effects since they were totally prevented by cyclosporin A and ADP. In contrast, the dicarboxylic analogue of 3HTA did not alter the tested parameters. Our data strongly indicate that 3HTA and 3HPA behave as metabolic inhibitors, uncouplers of oxidative phosphorylation and mPT inducers in skeletal muscle. It is proposed that these pathomechanisms disrupting mitochondrial homeostasis may be involved in the muscle alterations characteristic of MTP and LCHAD deficiencies.

Mitochondrial trifunctional protein deficiency in human cultured fibroblasts: effects of bezafibrate

Mitochondrial trifunctional protein (MTP) deficiency caused by HADHA or HADHB gene mutations exhibits substantial molecular, biochemical, and clinical heterogeneity and ranks among the more severe fatty acid oxidation (FAO) disorders, without pharmacological treatment. Since bezafibrate has been shown to potentially correct other FAO disorders in patient cells, we analyzed its effects in 26 MTP-deficient patient fibroblasts representing 16 genotypes. Overall, the patient cell lines exhibited variable, complex, biochemical profiles and pharmacological responses. HADHA-deficient fibroblasts showed markedly reduced alpha subunit protein levels together with decreased beta-subunit abundance, exhibited a -86 to -96% defect in LCHAD activity, and produced large amounts of C14 and C16 hydroxyacylcarnitines. In control fibroblasts, exposure to bezafibrate (400 μM for 48 h) increased the abundance of HADHA and HADHB mRNAs, immune-detectable alpha and beta subunit proteins, activities of LCHAD and LCKAT, and stimulated FAO capacities, clearly indicating that MTP is pharmacologically up-regulated by bezafibrate in human fibroblasts. In MTP-deficient patient fibroblasts, which were found markedly FAO-deficient, bezafibrate improved FAO capacities in six of 26 (23%) cases, including three cell lines heterozygous for the common c1528G > C mutation. Altogether, our results strongly suggest that, due to variable effects of HADHA and HADHB mutations on MTP abundance and residual activity, improvement of MTP deficiency in response to bezafibrate was achieved in a subset of responsive genotypes.

Neuropsychological Development in Patients with Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase (LCHAD) Deficiency

BACKGROUND

Reports on cognitive outcomes in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) are scarce. We present results from neuropsychological assessments of eight patients diagnosed with LCHADD prior to newborn screening with regard to clinical disease severity.

METHODS

Intellectual ability and adaptive and executive functions were assessed using age-appropriate Wechsler Scales, Adaptive Behavior Assessment Scales (ABAS), and Behavior Rating Inventory of Executive Function (BRIEF).

RESULTS

Five patients performed in the normal range on IQ tests but with lower scores on verbal working memory. In addition, they had lower parent-rated adaptive and executive functions.Three patients had intellectual disabilities with IQs below normal and/or autism spectrum disorders. In addition, they had low results on parent-rated adaptive functions. (Two of these patients had epilepsy.) Conclusions: Patients with LCHADD seem to have a specific cognitive pattern, with presentation as intellectual disability and specific autistic deficiencies or a normal IQ with weaknesses in auditive verbal memory and adaptive and executive functions. Future studies are warranted to investigate whether newborn screening programs and early treatment may promote improved neuropsychological development and outcomes.

Mitochondrial trifunctional protein deficiency due to HADHB gene mutation in a Chinese family

We report an 8-year-old girl with lower limb weakness since birth in whom mitochondrial trifunctional protein (MTP) deficiency, an autosomal recessive fatty acid oxidation disorder caused by HADHA or HADHB mutations, had not been definitively diagnosed before she was referred to our hospital. Repeated blood acylcarnitine analysis revealed slightly increased long-chain 3-OH-acylcarnitine levels; electromyography (EMG) suggested peripheral nerve injury; muscle biopsy confirmed a neurogenic lesion in muscle fibers, as shown by EMG. Analysis of the HADHB, which encodes long-chain 3-ketoacyl-CoA thiolase, one of the enzymes constituting mitochondrial trifunctional protein, identified homozygous missense mutation c.739C > T (p.R247C). Mitochondrial trifunctional protein deficiency is an extremely rare disorder and has not been reported in Chinese people to date. It is likely that neonatal onset, as seen in our patient, has not been reported for the neuromyopathic phenotype of mitochondrial trifunctional protein deficiency.

The investigation and management of metabolic myopathies

Metabolic myopathies (MM) are rare inherited primary muscle disorders that are mainly due to abnormalities of muscle energy metabolism resulting in skeletal muscle dysfunction. These diseases include disorders of fatty acid oxidation, glyco(geno)lytic muscle disorders and mitochondrial respiratory chain (MRC) disease. Clinically these disorders present with a range of symptoms including infantile hypotonia, myalgia/exercise tolerance, chronic or acute muscle weakness, cramps/spasms/stiffness or episodic acute rhabdomyolysis. The precipitant may be fasting, infection, general anaesthesia, heat/cold or most commonly, exercise. However, the differential diagnosis includes a wide range of both acquired and inherited conditions and these include exposure to drugs/toxins, inflammatory myopathies, dystrophies and channelopathies. Streamlining of existing diagnostic protocols has now become a realistic prospect given the availability of second-generation sequencing. A diagnostic pathway using a ‘rhabdomyolysis’ gene panel at an early stage of the diagnostic process is proposed. Following detailed clinical evaluation and first-line investigations, some patients will be identified as candidates for McArdle disease/glycogen storage disease type V or MRC disease and these will be referred directly to the specialised services. However, for the majority of patients, second-line investigation is best undertaken through next-generation sequencing using a ‘rhabdomyolysis’ gene panel. Following molecular analysis and careful evaluation of the findings, some patients will receive a clear diagnosis. Further functional or specific targeted testing may be required in other patients to evaluate the significance of uncertain/equivocal findings. For patients with no clear diagnosis, further investigations will be required through a specialist centre.

Uncoupling, metabolic inhibition and induction of mitochondrial permeability transition in rat liver mitochondria caused by the major long-chain hydroxyl monocarboxylic fatty acids accumulating in LCHAD deficiency

Patients with long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiency commonly present liver dysfunction whose pathogenesis is unknown. We studied the effects of long-chain 3-hydroxylated fatty acids (LCHFA) that accumulate in LCHAD deficiency on liver bioenergetics using mitochondrial preparations from young rats. We provide strong evidence that 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, the monocarboxylic acids that are found at the highest tissue concentrations in this disorder, act as metabolic inhibitors and uncouplers of oxidative phosphorylation. These conclusions are based on the findings that these fatty acids decreased ADP-stimulated (state 3) and uncoupled respiration, mitochondrial membrane potential and NAD(P)H content, and, in contrast, increased resting (state 4) respiration. We also verified that 3HTA and 3HPA markedly reduced Ca2+ retention capacity and induced swelling in Ca2+-loaded mitochondria. These effects were mediated by mitochondrial permeability transition (MPT) induction since they were totally prevented by the classical MPT inhibitors cyclosporin A and ADP, as well as by ruthenium red, a Ca2+ uptake blocker. Taken together, our data demonstrate that the major monocarboxylic LCHFA accumulating in LCHAD deficiency disrupt energy mitochondrial homeostasis in the liver. It is proposed that this pathomechanism may explain at least in part the hepatic alterations characteristic of the affected patients.

Diagnostic evaluation of rhabdomyolysis

Rhabdomyolysis is characterized by severe acute muscle injury resulting in muscle pain, weakness, and/or swelling with release of myofiber contents into the bloodstream. Symptoms develop over hours to days after an inciting factor and may be associated with dark pigmentation of the urine. Serum creatine kinase and urine myoglobin levels are markedly elevated. Clinical examination, history, laboratory studies, muscle biopsy, and genetic testing are useful tools for diagnosis of rhabdomyolysis, and they can help differentiate acquired from inherited causes of rhabdomyolysis. Acquired causes include substance abuse, medication or toxic exposures, electrolyte abnormalities, endocrine disturbances, and autoimmune myopathies. Inherited predisposition to rhabdomyolysis can occur with disorders of glycogen metabolism, fatty acid β-oxidation, and mitochondrial oxidative phosphorylation. Less common inherited causes of rhabdomyolysis include structural myopathies, channelopathies, and sickle-cell disease. This review focuses on the differentiation of acquired and inherited causes of rhabdomyolysis and proposes a practical diagnostic algorithm. Muscle Nerve 51: 793-810, 2015.

Increased and early lipolysis in children with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency during fast

Children with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHAD) have a defect in the degradation of long-chain fatty acids and are at risk of hypoketotic hypoglycemia and insufficient energy production as well as accumulation of toxic fatty acid intermediates. Knowledge on substrate metabolism in children with LCHAD deficiency during fasting is limited. Treatment guidelines differ between centers, both as far as length of fasting periods and need for night feeds are concerned. To increase the understanding of fasting intolerance and improve treatment recommendations, children with LCHAD deficiency were investigated with stable isotope technique, microdialysis, and indirect calometry, in order to assess lipolysis and glucose production during 6 h of fasting. We found an early and increased lipolysis and accumulation of long chain acylcarnitines after 4 h of fasting, albeit no patients developed hypoglycemia. The rate of glycerol production, reflecting lipolysis, averaged 7.7 ± 1.6 µmol/kg/min, which is higher compared to that of peers. The rate of glucose production was normal for age; 19.6 ± 3.4 µmol/kg/min (3.5 ± 0.6 mg/kg/min). Resting energy expenditure was also normal, even though the respiratory quotient was increased indicating mainly glucose oxidation. The results show that lipolysis and accumulation of long chain acylcarnitines occurs before hypoglycemia in fasting children with LCHAD, which may indicate more limited fasting tolerance than previously suggested.

Clinical outcome, biochemical and therapeutic follow-up in 14 Austrian patients with Long-Chain 3-Hydroxy Acyl CoA Dehydrogenase Deficiency (LCHADD)

Background

LCHADD is a long-fatty acid oxidation disorder with immediate symptoms and long-term complications. We evaluated data on clinical status, biochemical parameters, therapeutic regimens and outcome of Austrian LCHADD patients.

Study design

Clinical and outcome data including history, diagnosis, short- and long-term manifestations, growth, psychomotor development, hospitalizations, therapy of 14 Austrian patients with LCHADD were evaluated. Biochemically, we evaluated creatine kinase (CK) and acyl carnitine profiles.

Results

All LCHADD patients are homozygous for the common mutation. Three are siblings. Diagnosis was first established biochemically. Nine/14 (64%) were prematures, with IRDS occurring in six. In nine (64%), diagnosis was established through newborn screening, the remaining five (36%) were diagnosed clinically. Four pregnancies were complicated by HELLP syndrome, one by preeclampsia. In two, intrauterine growth retardation and placental insufficiency were reported. Five were diagnosed with hepatopathy at some point, seven with cardiomyopathy and eight with retinopathy, clinically relevant only in one patient. Polyneuropathy is only present in one. Three patients have a PEG, one is regularly fed via NG-tube. Growth is normal in all, as well as psychomotor development, except for two extremely premature girls. In 11 patients, 165 episodes with elevated creatine kinase concentrations were observed with 6-31 (median 14) per patient; three have shown no elevated CK concentrations. Median total carnitine on therapy was 19 μmol/l (range 11-61). For 14 patients, there have been 181 hospitalizations (median 9 per patient), comprising 1337 in-patient-days. All centres adhere to treatment with a fat-defined diet; patients have between 15% and 40% of their energy intake from fat (median 29%), out of which between 20% and 80% are medium-chain triglycerides (MCT) (median 62%). Four patients have been treated with heptanoate (C7).

Conclusion

Our data show LCHADD outcome can be favourable. Growth and psychomotor development is normal, except in two prematures. Frequency of CK measurements decreases with age, correlating with a decreasing number of hospitalizations. About 50% develop complications affecting different organ systems. There is no relevant difference between the patients treated in the respective centers. Concluding from single case reports, anaplerotic therapy with heptanoate should be further evaluated.

The clinical spectrum of inherited diseases involved in the synthesis and remodeling of complex lipids. A tentative overview

Over one hundred diseases related to inherited defects of complex lipids synthesis and remodeling are now reported. Most of them were described within the last 5 years. New descriptions and phenotypes are expanding rapidly. While the associated clinical phenotype is currently difficult to outline, with only a few patients identified, it appears that all organs and systems may be affected. The main clinical presentations can be divided into (1) Diseases affecting the central and peripheral nervous system. Complex lipid synthesis disorders produce prominent motor manifestations due to upper and/or lower motoneuron degeneration. Motor signs are often complex, associated with other neurological and extra-neurological signs. Three neurological phenotypes, spastic paraparesis, neurodegeneration with brain iron accumulation and peripheral neuropathies, deserve special attention. Many apparently well clinically defined syndromes are not distinct entities, but rather clusters on a continuous spectrum, like for the PNPLA6-associated diseases, extending from Boucher-Neuhauser syndrome via Gordon Holmes syndrome to spastic ataxia and pure hereditary spastic paraplegia; (2) Muscular/cardiac presentations; (3) Skin symptoms mostly represented by syndromic (neurocutaneous) and non syndromic ichthyosis; (4) Retinal dystrophies with syndromic and non syndromic retinitis pigmentosa, Leber congenital amaurosis, cone rod dystrophy, Stargardt disease; (5) Congenital bone dysplasia and segmental overgrowth disorders with congenital lipomatosis; (6) Liver presentations characterized mainly by transient neonatal cholestatic jaundice and non alcoholic liver steatosis with hypertriglyceridemia; and (7) Renal and immune presentations. Lipidomics and molecular functional studies could help to elucidate the mechanism(s) of dominant versus recessive inheritance observed for the same gene in a growing number of these disorders.

Two-dimensional gel electrophoresis of gastric tissue in an alkaline pH range

2DE in combination with MS has facilitated the discovery of several proteins with altered abundance in gastric cancer. While acidic and wide pH ranges have been widely investigated, analysis in the alkaline pH range has not been specifically performed in gastric cancer to date. In the present study, we initially optimized the 2DE in alkaline pH range (pH 7-11) for gastric tissue samples. Using a modified lysis buffer, we analyzed pooled nontumor and tumor samples for proteins with altered abundance in gastric adenocarcinoma. We successfully identified 38 silver-stained spots as 24 different proteins. Four of these were chosen for investigation with immunoblotting on individual paired samples to determine whether the changes seen in 2DE represent the overall abundance of the protein or possibly only a single form. While mitochondrial trifunctional protein (MTP) subunits were decreased in 2DE gels, immunoblotting identified their overall abundance as being differently dysregulated: in the gastric tumor samples, the MTP-α subunit was decreased, and the MTP-β subunit was increased. On the other hand, heterogenous nuclear ribonucleoprotein M and galectin-4 were increased in the gastric tumor samples in both 2DE and immunoblotting.

Pathophysiology of fatty acid oxidation disorders and resultant phenotypic variability

Fatty acids are a major fuel for the body and fatty acid oxidation is particularly important during fasting, sustained aerobic exercise and stress. The myocardium and resting skeletal muscle utilise long-chain fatty acids as a major source of energy. Inherited disorders affecting fatty acid oxidation seriously compromise the function of muscle and other highly energy-dependent tissues such as brain, nerve, heart, kidney and liver. Such defects encompass a wide spectrum of clinical disease, presenting in the neonatal period or infancy with recurrent hypoketotic hypoglycaemic encephalopathy, liver dysfunction, hyperammonaemia and often cardiac dysfunction. In older children, adolescence or adults there is often exercise intolerance with episodic myalgia or rhabdomyolysis in association with prolonged aerobic exercise or other exacerbating factors. Some disorders are particularly associated with toxic metabolites that may contribute to encephalopathy, polyneuropathy, axonopathy and pigmentary retinopathy. The phenotypic diversity encountered in defects of fat oxidation is partly explained by genotype/phenotype correlation and certain identifiable environmental factors but there remain many unresolved questions regarding the complex interaction of genetic, epigenetic and environmental influences that dictate phenotypic expression. It is becoming increasingly clear that the view that most inherited disorders are purely monogenic diseases is a naive concept. In the future our approach to understanding the phenotypic diversity and management of patients will be more realistically achieved from a polygenic perspective.

Novel proteins associated with human dilated cardiomyopathy: selective reduction in α(1A)-adrenergic receptors and increased desensitization proteins

Abstract Therapeutics to treat human heart failure (HF) and the identification of proteins associated with HF are still limited. We analyzed α(1)-adrenergic receptor (AR) subtypes in human HF and performed proteomic analysis on more uniform samples to identify novel proteins associated with human HF. Six failing hearts with end-stage dilated cardiomyopathy (DCM) and four non-failing heart controls were subjected to proteomic analysis. Out of 48 identified proteins, 26 proteins were redundant between samples. Ten of these 26 proteins were previously reported to be associated with HF. Of the newly identified proteins, we found several muscle proteins and mitochondrial/electron transport proteins, while novel were functionally similar to previous reports. However, we also found novel proteins involved in functional classes such as β-oxidation and G-protein coupled receptor signaling and desensitization not previously associated with HF. We also performed radioligand-binding studies on the heart samples and not only confirmed a large loss of β(1)-ARs in end-stage DCM, but also found a selective decrease in the α(1A)-AR subtype not previously reported. We have identified new proteins and functional categories associated with end-stage DCM. We also report that similar to the previously characterized loss of β(1)-AR in HF, there is also a concomitant loss of α(1A)-ARs, which are considered cardioprotective proteins.

Observations regarding retinopathy in mitochondrial trifunctional protein deficiencies

Although the retina is thought to primarily rely on glucose for fuel, inherited deficiency of one or more activities of mitochondrial trifunctional protein results in a pigmentary retinopathy leading to vision loss. Many other enzymatic deficiencies in fatty acid oxidation pathways have been described, none of which results in retinal complications. The etiology of retinopathy among patients with defects in trifunctional protein is unknown. Trifunctional protein is a heteroctomer; two genes encode the alpha and beta subunits of TFP respectively, HADHA and HADHB. A common mutation in HADHA, c.1528G>C, leads to a single amino acid substitution, p. Glu474Gln, and impairs primarily long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) activity leading to LCHAD deficiency (LCHADD). Other mutations in HADHA or HADHB often lead to significant reduction in all three enzymatic activities and result in trifunctional protein deficiency (TFPD). Despite many similarities in clinical presentation and phenotype, there is growing evidence that they can result in different chronic complications. This review will outline the clinical similarities and differences between LCHADD and TFPD, describe the course of the associated retinopathy, propose a genotype/phenotype correlation with the severity of retinopathy, and discuss the current theories about the etiology of the retinopathy.

Necrotizing enterocolitis and respiratory distress syndrome as first clinical presentation of mitochondrial trifunctional protein deficiency

BACKGROUND

Newborn screening (NBS) for long-chain 3-hydroxy acyl-CoA dehydrogenase (LCHAD) deficiency does not discriminate between isolated LCHAD deficiency, isolated long-chain keto acyl-CoA (LCKAT) deficiency and general mitochondrial trifunctional protein (MTP) deficiency. Therefore, screening for LCHAD deficiency inevitably comprises screening for MTP deficiency, which is much less amenable to treatment. Furthermore, absence of a clear classification system for these disorders is still lacking.

MATERIALS AND METHODS

Two newborns screened positive for LCHAD deficiency died at the age of 10 and 31 days, respectively. One due to severe necrotizing enterocolitis (NEC), cardiomyopathy and multiorgan failure and the other due to severe infant respiratory distress syndrome (IRDS) and hypertrophic cardiomyopathy. (Keto)-acylcarnitine concentration and enzymatic analysis of LCHAD and LCKAT suggested MTP deficiency in both patients. Mutation analysis revealed a homozygous HADHB c.357+5delG mutation in one patient and a homozygous splice-site HADHB mutation c.212+1G>C in the other patient.Data on enzymatic and mutation analysis of 40 patients with presumed LCHAD, LCKAT or MTP deficiency were used to design a classification to distinguish between these disorders.

DISCUSSION

NEC as presenting symptom in MTP deficiency has not been reported previously. High expression of long-chain fatty acid oxidation enzymes reported in lungs and gut of human foetuses suggests that the severe NEC and IRDS observed in our patients are related to the enzymatic deficiency in these organs during crucial stages of development.Furthermore, as illustrated by the cases we propose a classification system to discriminate LCHAD, LCKAT and MTP deficiency based on enzymatic analysis.

Prevalence of Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency in Estonia

The aim of our study was to evaluate the prevalence of long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) in the general Estonian population and among patients with symptoms suggestive of fatty acid oxidation (FAO) defects. We collected DNA from a cohort of 1,040 anonymous newborn blood spot samples. We screened these samples for the presence of the common c.1528G>C mutation in the HADHA gene. Based on the clinical suspicion of FAO defects, we screened suspected individuals since 2004 for the common c.1528G>C mutation in the HADHA gene and since 2008 in addition by tandem mass spectrometric analysis of plasma acylcarnitines. Our results showed that the carrier frequency of the c.1528G>C mutation in the Estonian population is high - 1:173. During the screening of symptomatic patients, we identified five LCHADD patients in four families. Three patients were retrospectively identified by molecular screening of the HADHA gene. One patient was homozygous for the c.1528G>C mutation in the HADHA gene, and two siblings were compound heterozygotes with HADHA genotype c.[1528G>C]+[1690-2A>G]. Among patients tested using acylcarnitine profiling, we identified two cases with an abnormal acylcarnitine profile typical to LCHADD. Molecular analysis showed homozygosity for c.1528G>C mutation. Based on a carrier frequency of 1:173 (95% Confidence Interval 1:76-1:454) and taking into account that the c.1528G>C mutation makes up 87.5% of disease alleles in Estonian LCHADD patients, the estimated prevalence of LCHADD in Estonia would be 1: 91,700.

Comprehensive cDNA study and quantitative analysis of mutant HADHA and HADHB transcripts in a French cohort of 52 patients with mitochondrial trifunctional protein deficiency

BACKGROUND

Deficiency of mitochondrial trifunctional protein (MTP) is caused by mutations in the HADHA and HADHB genes, which have been mostly delineated at the genomic DNA level and have not been always elucidated.

AIM

To identify mutations in a French cohort of 52 MTP deficient patients and the susceptibility of mutations generating premature termination codons (PTCs) to the nonsense mRNA mediated decay (NMD).

METHODS

Mutation screening in fibroblasts was performed at the cDNA level and real-time RT-PCR was used to compare the levels of the different PTC-bearing mRNAs before and after a treatment of fibroblasts by emetine, a translation inhibitor.

RESULTS

A mutation detection rate of 100% was achieved. A total of 22 novel mutations were identified, including a large-sized genomic deletion in HADHB gene. A high proportion of all identified mutations were non-sense, frameshift and splicing mutations, generating (PTCs), distributed essentially on HADHA coding regions. We could demonstrate that the majority of mutations resulting in PTCs conform to the established rules governing the susceptibility to NMD.

CONCLUSION

Our results emphasize the value of cDNA analysis in the characterization of HADHA and HADHB mutations and further strengthen the model of haploinsufficiency as a major pathomechanism in MTP defects.

Urgent metabolic service improves survival in long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency detected by symptomatic identification and pilot newborn screening

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a fatty acid oxidation disorder with especially high mortality and uncertain long-term outcome. The aim of the study was to analyze the influence of diagnostic approach on survival in 59 affected children. Referral to a metabolic center was replaced over time by urine/blood testing in centralized metabolic laboratory (selective screening) and by pilot tandem mass spectrometry newborn screening (NBS). Molecular analysis revealed the prevalent mutation in the HADHA gene in all 58 examined cases. Twenty patients died. The number of detections and number of deaths were respectively 9 and 4 (44%) in the patients recognized by differential diagnosis, 28 and 9 (32%) - by selective screening, and 11 and 1 (9%) - by NBS. In 80% of cases the death occurred before or within 3 weeks from the identification. Urgent and active metabolic service remarkably influenced the surviving. The current age of 39 survivors is 0.5 to 23 yrs (mean 7.2 yrs). The disease frequency estimated on the patients number was 1: 115 450, whereas in the pilot NBS - 1: 109 750 (658 492 neonates tested). Interestingly, the phenylalanine level in asymptomatic neonates frequently exceeded the cut-off values.

CONCLUSIONS

1) Urgent metabolic intervention decreases mortality of LCHAD-deficient patients, but the prognosis is still uncertain. 2) Emergent metabolic reporting and service are crucial also for the survival of neonates detected by NBS. 3) The nationwide selective screening appeared efficient in LCHADD detection in the country. 4) Transient mild hyperphenylalaninaemia may occur in LCHAD-deficient newborns.

Disorders of muscle lipid metabolism: diagnostic and therapeutic challenges

Disorders of muscle lipid metabolism may involve intramyocellular triglyceride degradation, carnitine uptake, long-chain fatty acids mitochondrial transport, or fatty acid β-oxidation. Three main diseases leading to permanent muscle weakness are associated with severe increased muscle lipid content (lipid storage myopathies): primary carnitine deficiency, neutral lipid storage disease and multiple acyl-CoA dehydrogenase deficiency. A moderate lipidosis may be observed in fatty acid oxidation disorders revealed by rhabdomyolysis episodes such as carnitine palmitoyl transferase II, very-long-chain acyl-CoA dehydrogenase, mitochondrial trifunctional protein deficiencies, and in recently described phosphatidic acid phosphatase deficiency. Respiratory chain disorders and congenital myasthenic syndromes may also be misdiagnosed as fatty acid oxidation disorders due to the presence of secondary muscle lipidosis. The main biochemical tests giving clues for the diagnosis of these various disorders are measurements of blood carnitine and acylcarnitines, urinary organic acid profile, and search for intracytoplasmic lipid on peripheral blood smear (Jordan's anomaly). Genetic analysis orientated by the results of biochemical investigation allows establishing a firm diagnosis. Primary carnitine deficiency and multiple acyl-CoA dehydrogenase deficiency may be treated after supplementation with carnitine, riboflavine and coenzyme Q10. New therapeutic approaches for fatty acid oxidation disorders are currently developed, based on pharmacological treatment with bezafibrate, and specific diets enriched in medium-chain triglycerides or triheptanoin.

Disturbance of mitochondrial energy homeostasis caused by the metabolites accumulating in LCHAD and MTP deficiencies in rat brain

AIMS

We investigated the in vitro effects of 3-hydroxydodecanoic (3HDA), 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, which accumulate in tissues of patients affected by mitochondrial trifunctional protein (MTP) and isolated long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiencies, on various parameters of energy homeostasis in mitochondrial preparations from brain of young rats.

MAIN METHODS

We measured the respiratory parameters state 4, state 3, respiratory control ratio (RCR) and ADP/O ratio by the rate of oxygen consumption, as well as the mitochondrial membrane potential and the matrix NAD(P)H levels in the presence of the fatty acids.

KEY FINDINGS

We found that 3HDA, 3HTA and 3HPA markedly increased state 4 respiration and diminished the RCR using glutamate plus malate or succinate as substrates. 3HTA and 3HPA also diminished the mitochondrial membrane potential and the matrix NAD(P)H levels. In addition, 3HTA decreased state 3 respiration using glutamate/malate, but not pyruvate/malate or succinate as substrates. Our data indicate that the long-chain 3-hydroxy fatty acids that accumulate in LCHAD/MTP deficiencies act as uncouplers of oxidative phosphorylation, while 3HTA also behaves as a metabolic inhibitor.

SIGNIFICANCE

It is presumed that impairment of brain energy homeostasis caused by these endogenous accumulating compounds may contribute at least in part to the neuropathology of LCHAD/MTP deficiencies.

Clinical and molecular aspects of Japanese patients with mitochondrial trifunctional protein deficiency

Mitochondrial trifunctional protein (MTP) deficiency is a rare inherited metabolic disorder of mitochondrial fatty acid oxidation. We newly characterized three novel mutations in 2 Japanese patients with MTP deficiency, and investigated the clinical and molecular aspects of 5 Japanese patients including 3 previously reported cases. Herein, we describe the characterization of four missense mutations, R214C, H346R, R411K, and V422G, in the HADHB gene, which have been identified in Japanese patients, employing a newly developed, sensitive transient expression analysis. Co-transfection of wild-type HADHA and HADHB cDNAs in SV40-transfected fibroblasts from a MTP-deficient patient yielded sufficient enzyme activity to evaluate low-level residual enzyme activity, using two incubation temperatures of 30 degrees C and 37 degrees C. At 30 degrees C, residual enzyme activity was higher than that at 37 degrees C in V422G, R214C, and R411K. However, H346R, which was seen in the most severe case, showed no enzyme activity at both temperatures. Our results demonstrate that a defect of HADHB in MTP deficiency is rather common in Japanese patients, and the mutational spectrum is heterogeneous. The present findings showed that all missense mutations in this study were disease-causing. Although the number of patients is still limited, it is suggested that the phenotype is correlated with the genotype and a combination of two mutant alleles of the HADHB gene in MTP deficiency.

Acute dilated cardiomyopathy in a patient with deficiency of long-chain 3-hydroxyacyl-CoA dehydrogenase

Deficiency of long-chain 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase (LCHADD) is a rare inborn error of metabolism. It is associated with hypertrophic cardiomyopathy and less frequently with dilated cardiomyopathy. The incidence and pathophysiology of cardiac involvement in LCHADD is poorly understood. This report describes the acute decompensation of a 3-year-old girl who had LCHADD with rapidly developing dilated cardiomyopathy. A review of the literature and possible causes of cardiomyopathy in LCHADD are explored.

Study of deep intronic sequence exonization in a Japanese neonate with a mitochondrial trifunctional protein deficiency

Mitochondrial trifunctional protein (MTP) comprises heterooctamer alpha4beta4 and a deficiency in this protein causes a mitochondrial long-chain beta-oxidation defect. Here, we describe the molecular basis of an MTPbeta-subunit deficiency in a Japanese neonate. Mutation screening at the genomic level including all exons and exon-intron boundaries identified a novel c.1136A>G (H346R) mutation in exon 13 of the maternal allele, but none in the paternal allele. Analysis by RT-PCR identified paternal-specific 106- and 56-bp intronic insertions between exons 7 and 8, which introduced premature terminations. This intronic exonization was caused by a deep intronic mutation in intron 7 on the paternal allele that generates a cryptic splice donor site. This is the first report of a deep intronic mutation in MTP deficiency.

A new genetic disorder in mitochondrial fatty acid beta-oxidation: ACAD9 deficiency

The acyl-CoA dehydrogenases are a family of multimeric flavoenzymes that catalyze the alpha,beta -dehydrogenation of acyl-CoA esters in fatty acid beta -oxidation and amino acid catabolism. Genetic defects have been identified in most of the acyl-CoA dehydrogenases in humans. Acyl-CoA dehydrogenase 9 (ACAD9) is a recently identified acyl-CoA dehydrogenase that demonstrates maximum activity with unsaturated long-chain acyl-CoAs. We now report three cases of ACAD9 deficiency. Patient 1 was a 14-year-old, previously healthy boy who died of a Reye-like episode and cerebellar stroke triggered by a mild viral illness and ingestion of aspirin. Patient 2 was a 10-year-old girl who first presented at age 4 mo with recurrent episodes of acute liver dysfunction and hypoglycemia, with otherwise minor illnesses. Patient 3 was a 4.5-year-old girl who died of cardiomyopathy and whose sibling also died of cardiomyopathy at age 21 mo. Mild chronic neurologic dysfunction was reported in all three patients. Defects in ACAD9 mRNA were identified in the first two patients, and all patients manifested marked defects in ACAD9 protein. Despite a significant overlap of substrate specificity, it appears that ACAD9 and very-long-chain acyl-CoA dehydrogenase are unable to compensate for each other in patients with either deficiency. Studies of the tissue distribution and gene regulation of ACAD9 and very-long-chain acyl-CoA dehydrogenase identify the presence of two independently regulated functional pathways for long-chain fat metabolism, indicating that these two enzymes are likely to be involved in different physiological functions.

Long chain fatty acid oxidation defects in children: importance of detection and treatment options

BACKGROUND

Mitochondrial beta oxidation plays a major role in energy production. Long chain fatty acid oxidation defects include deficiency of the trifunctional protein (rare) or more commonly defects of the long chain 3-hydroxy acyl-CoA dehydrogenase enzyme (LCHAD). These long chain defects have variable presentations, they may present in the neonate or infant with sudden death, hepatopathy (Reyes disease), hypoketotic hypoglycaemia, rhabdomyolysis, myopathy, cardiomyopathy and with late complications such as peripheral neuropathy, pigmentary retinopathy, retinal degeneration and progressive visual loss. The correct diagnosis at presentation is not only life saving but also allows for the appropriate dietary and other intervention, which may have major effects on outcome.

AIM

Three case reports of patients with long chain fatty acid oxidation defects who have shown significant benefits from treatment are reported.

CONCLUSIONS

These paediatric presentations illustrate the clinical heterogeneity of long chain fatty acid oxidation defects and opportunities for effective management if correctly diagnosed.

ENU mutagenesis identifies mice with cardiac fibrosis and hepatic steatosis caused by a mutation in the mitochondrial trifunctional protein beta-subunit

Using the metabolomics-guided screening coupled to N-ethyl-N-nitrosourea-mediated mutagenesis, we identified mice that exhibited elevated levels of long-chain acylcarnitines. Whole genome homozygosity mapping with 262 SNP markers mapped the disease gene to chromosome 5 where candidate genes Hadha and Hadhb, encoding the mitochondria trifunctional protein (MTP) alpha- and beta-subunits, respectively, are located. Direct sequencing revealed a normal alpha-subunit, but detected a nucleotide T-to-A transversion in exon 14 (c.1210T>A) of beta-subunit (Hadhb) which resulted in a missense mutation of methionine to lysine (M404K). Western blot analysis showed a significant reduction of both the alpha- and beta-subunits, consistent with reduced enzyme activity in both the long-chain 3-hydroxyacyl-CoA dehydrogenase and the long-chain 3-ketoacyl-CoA thiolase activities. These mice had a decreased weight gain and cardiac arrhythmias which manifested from a prolonged PR interval to a complete atrio-ventricular dissociation, and died suddenly between 9 and 16 months of age. Histopathological studies showed multifocal cardiac fibrosis and hepatic steatosis. This mouse model will be useful to further investigate the mechanisms underlying arrhythmogenesis relating to lipotoxic cardiomyopathy and to investigate pathophysiology and treatment strategies for human MTP deficiency.