Clear correlation of genotype with disease phenotype in very-long-chain acyl-CoA dehydrogenase deficiency

Inborn errors of energy metabolism associated with myopathies

Inherited neuromuscular disorders affect approximately one in 3,500 children. Structural muscular defects are most common; however functional impairment of skeletal and cardiac muscle in both children and adults may be caused by inborn errors of energy metabolism as well. Patients suffering from metabolic myopathies due to compromised energy metabolism may present with exercise intolerance, muscle pain, reversible or progressive muscle weakness, and myoglobinuria. In this review, the physiology of energy metabolism in muscle is described, followed by the presentation of distinct disorders affecting skeletal and cardiac muscle: glycogen storage diseases types III, V, VII, fatty acid oxidation defects, and respiratory chain defects (i.e., mitochondriopathies). The diagnostic work-up and therapeutic options in these disorders are discussed.

Effect of heat stress and bezafibrate on mitochondrial beta-oxidation: comparison between cultured cells from normal and mitochondrial fatty acid oxidation disorder children using in vitro probe acylcarnitine profiling assay

Hyperpyrexia occasionally triggers acute life-threatening encephalopathy-like illnesses, including influenza-associated encephalopathy (IAE) in childhood, and can be responsible for impaired fatty acid beta-oxidation (FAO). In this regard, patients with impaired FAO may be more susceptible to febrile episodes. The effects of heat stress and a hypolipidemic drug, bezafibrate, on mitochondrial FAO were investigated using cultured cells from children with FAO disorders and from normal controls, using an in vitro probe acylcarnitine (AC) profiling assay. Fibroblasts were incubated in medium loaded with unlabelled palmitic acid for 96 h at 37 and 41 degrees C, with or without bezafibrate. AC profiles in culture medium were analyzed by electrospray ionization tandem mass spectrometry. Heat stress, introduced by 41 degrees C, significantly increased acetylcarnitine (C2) but slightly decreased the other acylcarnitines (ACs) in controls and medium-chain acyl-CoA dehydrogenase (MCAD)-deficient cells. On the other hand, in very long-chain acyl-CoA dehydrogenase (VLCAD)-deficient cells, accumulation of long-chain ACs were enhanced at 41 degrees C, compared with that at 37 degrees C. In contrast, bezafibrate decreased long-chain ACs with significant increase of C2 in both control and VLCAD-deficient cells at 37 degrees C. These data suggest that heat stress specifically inhibits long-chain FAO, whereas bezafibrate recovers the impaired FAO. Our approach is a simple and promising strategy to evaluate the effects of heat stress or therapeutic drugs on mitochondrial FAO.

Very long-chain acyl-CoA dehydrogenase deficiency in a patient with normal newborn screening by tandem mass spectrometry

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) can be detected through newborn screening with tandem mass spectrometry. We report a patient who died as a result of severe brain injury due to hypoglycemia. Newborn screening was normal. Postmortem enzyme analysis and molecular testing confirmed the diagnosis of VLCADD.

Compared effects of missense mutations in Very-Long-Chain Acyl-CoA Dehydrogenase deficiency: Combined analysis by structural, functional and pharmacological approaches

Very-Long-Chain Acyl-CoA Dehydrogenase deficiency (VLCADD) is an autosomal recessive disorder considered as one of the more common ss-oxidation defects, possibly associated with neonatal cardiomyopathy, infantile hepatic coma, or adult-onset myopathy. Numerous gene missense mutations have been described in these VLCADD phenotypes, but only few of them have been structurally and functionally analyzed, and the molecular basis of disease variability is still poorly understood. To address this question, we first analyzed fourteen disease-causing amino acid changes using the recently described crystal structure of VLCAD. The predicted effects varied from the replacement of amino acid residues lining the substrate binding cavity, involved in holoenzyme-FAD interactions or in enzyme dimerisation, predicted to have severe functional consequences, up to amino acid substitutions outside key enzyme domains or lying on near enzyme surface, with predicted milder consequences. These data were combined with functional analysis of residual fatty acid oxidation (FAO) and VLCAD protein levels in patient cells harboring these mutations, before and after pharmacological stimulation by bezafibrate. Mutations identified as detrimental to the protein structure in the 3-D model were generally associated to profound FAO and VLCAD protein deficiencies in the patient cells, however, some mutations affecting FAD binding or monomer-monomer interactions allowed a partial response to bezafibrate. On the other hand, bezafibrate restored near-normal FAO rates in some mutations predicted to have milder consequences on enzyme structure. Overall, combination of structural, biochemical, and pharmacological analysis allowed assessment of the relative severity of individual mutations, with possible applications for disease management and therapeutic approach.

Very long-chain acyl-CoA dehydrogenase deficiency: the effects of accidental fat loading in a patient detected through newborn screening

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is an autosomal recessive disorder of fatty acid oxidation. The majority of patients with VLCADD can be detected through newborn screening (NBS) with elevated levels of the tetradecanoyl carnitine species. An 11-month-old infant, diagnosed with late-onset VLCADD (genotype: T848C/G1322A) through newborn screening at birth, was admitted with emesis, severe lethargy, limpness in extremities, loss of muscle tone and an elevated CK level. He was mistakenly given Ketocal formula (about 8 g/kg per day long-chain fat-over six times his usual intake) instead of his usual Monogen formula for 2.5 days before being admitted. Once admitted, he was started on Monogen and IV (10% dextrose) fluids. He was discharged home after four days in the hospital without any sequelae of this accidental fat loading event. The report highlights several important points about this particular case and more generally about patients with VLCADD detected through NBS: (1) the amount of time in which patients might become severely symptomatic and the nature of these symptoms after fat loading; (2) the time frame for complete recovery after beginning of treatment; (3) the importance of alerting home-care companies and families about formula delivery errors and their repercussions.

Cardiac hypertrophy in mice with long-chain acyl-CoA dehydrogenase or very long-chain acyl-CoA dehydrogenase deficiency

Cardiac hypertrophy is a common finding in human patients with inborn errors of long-chain fatty acid oxidation. Mice with either very long-chain acyl-coenzyme A dehydrogenase deficiency (VLCAD-/-) or long-chain acyl-coenzyme A dehydrogenase deficiency (LCAD-/-) develop cardiac hypertrophy. Cardiac hypertrophy, initially measured using heart/body weight ratios, was manifested most severely in LCAD-/- male mice. VLCAD-/- mice, as a group, showed a mild increase in normalized cardiac mass (8.8% hypertrophy compared with all wild-type (WT) mice). In contrast, LCAD-/- mice as a group showed more severe cardiac hypertrophy (32.2% increase compared with all WT mice). On the basis of a clear male predilection, we analyzed the role of dietary plant estrogenic compounds commonly found in mouse diets because of soy or alfalfa components providing natural phytoestrogens or isoflavones in cardioprotection of LCAD-/- mice. Male LCAD-/- mice fed an isoflavone-free test diet had more severe cardiac hypertrophy (58.1% hypertrophy compared with WT mice fed the same diet). There were no significant differences in the female groups fed any of the diets. Echocardiography measurement performed on male LCAD-deficient mice fed a standard diet at the age of approximately 3 months confirmed the substantial cardiac hypertrophy in these mice compared with WT controls. Left ventricular (LV) wall thickness of the interventricular septum and posterior wall was remarkably increased in LCAD-/- mice compared with that of WT controls. Accordingly, the calculated LV mass after normalization to body weight was increased by about 40% in the LCAD-/- mice compared with WT mice. In summary, we found that metabolic cardiomyopathy, expressed as hypertrophy, developed in mice because of either VLCAD deficiency or LCAD deficiency; however, LCAD deficiency was the most profound and seemed to be attenuated either by endogenous estrogen (in females) or by phytoestrogens present in the diet as isoflavones (in males).

Dysregulation of very long chain acyl-CoA dehydrogenase coupled with lipid peroxidation

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease of unknown etiology. We previously revealed increased oxidative stress and high expression of antioxidant proteins in culture cell lines established from lesional lung tissues with IPF (Kabuyama Y, Oshima K, Kitamura T, Homma M, Yamaki J, Munakata M, Homma Y. Genes Cells 12: 1235-1244, 2007). In this study, we show that IPF cells contain high levels of free cholesterol and its peroxidized form as compared with normal TIG7 lung fibroblasts, suggesting that radical oxygen species (ROS) are generated within specific organelles. To understand the molecular basis underlying the generation of ROS in IPF cells, we performed proteomic analysis of mitochondrial proteins from TIG and IPF cells. This analysis shows that the phosphorylation of Ser586 of very long chain acyl-CoA dehydrogenase (VLCAD) is significantly reduced in IPF cells. Similar results are obtained from immunoblotting with anti-pS586 antibody. Kinase activity toward a peptide containing Ser586 from IPF cells is significantly lower than that from TIG cells. Furthermore, a phosphorylation-negative mutant (S586A) VLCAD shows reduced electron transfer activity and a strong dominant-negative effect on fatty acid beta-oxidation. The ectopic expression of the S586A mutant induced human embryonic kidney (HEK) 293 cells to produce significantly high amounts of oxidized lipids and hydrogen peroxide. HEK293 cells expressing the S586A mutant exhibit a reduction in cell growth and an enhancement in apoptosis. These results suggest a novel regulatory mechanism for homeostatic VLCAD activity, whose dysregulation might be involved in the production of oxidative stress and in the pathogenesis of IPF.

Treatment recommendations in long-chain fatty acid oxidation defects: consensus from a workshop

Published data on treatment of fatty acid oxidation defects are scarce. Treatment recommendations have been developed on the basis of observations in 75 patients with long-chain fatty acid oxidation defects from 18 metabolic centres in Central Europe. Recommendations are based on expert practice and are suggested to be the basis for further multicentre prospective studies and the development of approved treatment guidelines. Considering that disease complications and prognosis differ between different disorders of long-chain fatty acid oxidation and also depend on the severity of the underlying enzyme deficiency, treatment recommendations have to be disease-specific and depend on individual disease severity. Disorders of the mitochondrial trifunctional protein are associated with the most severe clinical picture and require a strict fat-reduced and fat-modified (medium-chain triglyceride-supplemented) diet. Many patients still suffer acute life-threatening events or long-term neuropathic symptoms despite adequate treatment, and newborn screening has not significantly changed the prognosis for these severe phenotypes. Very long-chain acyl-CoA dehydrogenase deficiency recognized in neonatal screening, in contrast, frequently has a less severe disease course and dietary restrictions in many patients may be loosened. On the basis of the collected data, recommendations are given with regard to the fat and carbohydrate content of the diet, the maximal length of fasting periods and the use of l-carnitine in long-chain fatty acid oxidation defects.

Novel mutation of early, perinatal-onset, myopathic-type very-long-chain acyl-CoA dehydrogenase deficiency

A male neonate demonstrated fetal distress, neonatal asphyxia, and transient hyper-creatine kinase-emia (8400IU/L), followed by repeated episodes of rhabdomyolysis 1-2 times/year during infancy and early childhood. At age 6 years, decreased levels of total and free carnitine in serum, and mild fiber size variation and increased fatty droplets in muscle, were confirmed. Both blood and serum fatty-acid analysis demonstrated elevated 5-tetradecenoate levels, and the acyl-CoA dehydrogenase activity of the palmitoyl-CoA/octanoyl-CoA ratio decreased in skin fibroblasts. The sequenced clone analysis of a complimentary DNA fragment revealed a compound heterozygote mutation of exon 9 (A790G) and exon 10 (997 ins T), which is a novel mutation of a myopathic-type very-long-chain acyl-CoA dehydrogenase deficiency. The patient has reached age 13 years. By treatment with an avoidance of fasting, feeding with a high-carbohydrate and low-fat diet, and intravenous drip infusion soon after every onset of rhabdomyolysis, his physical and mental development has stayed within the normal range. Patients with a perinatal onset of myopathic-type very-long-chain acyl-CoA dehydrogenase deficiency have not yet been reported. His novel mutation might be related to his clinical characterization.

Management and outcome in 75 individuals with long-chain fatty acid oxidation defects: results from a workshop

At present, long-chain fatty acid oxidation (FAO) defects are diagnosed in a number of countries by newborn screening using tandem mass spectrometry. In the majority of cases, affected newborns are asymptomatic at time of diagnosis and acute clinical presentations can be avoided by early preventive measures. Because evidence-based studies on management of long-chain FAO defects are lacking, we carried out a retrospective analysis of 75 patients from 18 metabolic centres in Germany, Switzerland, Austria and the Netherlands with special regard to treatment and disease outcome. Dietary treatment is effective in many patients and can prevent acute metabolic derangements and prevent or reverse severe long-term complications such as cardiomyopathy. However, 38% of patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency had intermittent muscle weakness and pain despite adhering to therapy. Seventy-six per cent of patients with disorders of the mitochondrial trifunctional protein (TFP)-complex including long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, had long-term myopathic symptoms. Of these, 21% had irreversible peripheral neuropathy and 43% had retinopathy. The main principle of treatment was a fat-reduced and fat-modified diet. Fat restriction differed among patients with different enzyme defects and was strictest in disorders of the TFP-complex. Patients with a medium-chain fat-based diet received supplementation of essential long-chain fatty acids. l-Carnitine was supplemented in about half of the patients, but in none of the patients with VLCAD deficiency identified by newborn screening. In summary, in this cohort the treatment regimen was adapted to the severity of the underlying enzyme defect and thus differed among the group of long-chain FAO defects.

Atypical presentation of VLCAD deficiency associated with a novel ACADVL splicing mutation

Very long chain acyl-CoA dehydrogenase (VLCAD) deficiency is an autosomal recessive inborn error of metabolism characterized by impaired mitochondrial beta-oxidation of fatty acids with a chain length between 14 and 18 carbons. While expansion of newborn screening has improved our ability to detect VLCAD deficiency in early childhood, the late-onset form of the disease still presents a significant diagnostic challenge. We report a 20-year-old female with VLCAD deficiency who first presented in infancy with hypoketotic hypoglycemia. In childhood the patient developed complex partial seizures that were aggravated by Lamotrigine treatment. The clinical course in early adulthood was complicated by recurrent, often unprovoked, episodes of rhabdomyolysis and myoglobinuria. In addition, she suffered from chronic myalgia, muscle weakness, and diffuse abdominal tenderness. A muscle biopsy revealed accumulation of fat droplets. Her acylcarnitine profile showed significantly elevated C14, C14:1, C16, and C18-carnitines. Sequence analysis of ACADVL revealed a heterozygous recurrent mutation c.848T>C (p.V283A) and a heterozygous novel splice mutation c.879-8T>A that results in the inclusion of six nucleotides from intron 9 into the transcript sequence. The molecular characterization of this novel mutation and its correlation with the clinical phenotype are discussed.

Diagnostic assessment and long-term follow-up of 13 patients with Very Long-Chain Acyl-Coenzyme A dehydrogenase (VLCAD) deficiency

Very Long-Chain Acyl-CoA dehydrogenase (VLCAD) deficiency is an inborn error of mitochondrial long-chain fatty acid oxidation (FAO) most often occurring in childhood with cardiac or liver involvement, but rhabdomyolysis attacks have also been reported in adults. We report in this study the clinical, biochemical and molecular studies in 13 adult patients from 10 different families with VLCAD deficiency. The enzyme defect was demonstrated in cultured skin fibroblasts or lymphocytes. All patients exhibited exercise intolerance and recurrent rhabdomyolysis episodes, which were generally triggered by strenuous exercise, fasting, cold or fever (mean age at onset: 10 years). Inaugural life-threatening general manifestations also occurred before the age of 3 years in four patients. Increased levels of long-chain acylcarnitines with tetradecenoylcarnitine (C14:1) as the most prominent species were observed in all patients. Muscle biopsies showed a mild lipidosis in four patients. For all patients but two, molecular analysis showed homozygous (4 patients) or compound heterozygous genotype (7 patients). For the two remaining patients, only one mutation in a heterozygous state was detected. This study confirms that VLCAD deficiency, although being less frequent than CPT II deficiency, should be systematically considered in the differential diagnosis of exercise-induced rhabdomyolysis. Measurement of fasting blood acylcarnitines by tandem mass spectrometry allows accurate biochemical diagnosis and should therefore be performed in all patients presenting with unexplained muscle exercise intolerance or rhabdomyolysis.

A Delphi clinical practice protocol for the management of very long chain acyl-CoA dehydrogenase deficiency

INTRODUCTION

Very long chain acyl-CoA dehydrogenase (VLCAD) deficiency is a disorder of oxidation of long chain fat, and can present as cardiomyopathy or fasting intolerance in the first months to years of life, or as myopathy in later childhood to adulthood. Expanded newborn screening has identified a relatively high incidence of this disorder (1:31,500), but there is a dearth of evidence-based outcomes data to guide the development of clinical practice protocols. This consensus protocol is intended to assist clinicians in the diagnosis and management of screen-positive newborns for VLCAD deficiency until evidence-based guidelines are available.

METHOD

The Oxford Centre for Evidence-based Medicine system was used to grade the literature review and create recommendations graded from A (evidence level of randomized clinical trials) to D (expert opinion). Delphi was used as the consensus tool. A panel of 14 experts (including clinicians, diagnostic laboratory directors and researchers) completed three rounds of survey questions and had a face-to-face meeting.

RESULT

Panelists reviewed the initial evaluation of the screen-positive infant, diagnostic testing and management of diagnosed patients. Grade C and D consensus recommendations were made in each of these three areas. The panel did not reach consensus on all issues, particularly in the dietary management of asymptomatic infants diagnosed by newborn screening.

Mitochondrial fatty acid oxidation defects--remaining challenges

Mitochondrial fatty acid oxidation defects have been recognized since the early 1970s. The discovery rate has been rather constant, with 3-4 'new' disorders identified every decade and with the most recent example, ACAD9 deficiency, reported in 2007. In this presentation we will focus on three of the 'old' defects: medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, riboflavin responsive multiple acyl-CoA dehydrogenation (RR-MAD) deficiency, and short-chain acyl-CoA dehydrogenase (SCAD) deficiency. These disorders have been discussed in many publications and at countless conference presentations, and many questions relating to them have been answered. However, continuing clinical and pathophysiological research has raised many further questions, and new ideas and methodologies may be required to answer these. We will discuss these challenges. For MCAD deficiency the key question is why 80% of symptomatic patients are homozygous for the prevalent ACADM gene variation c.985A > G whereas this is found in only approximately 50% of newborns with a positive screen. For RR-MAD deficiency, the challenge is to find the connection between variations in the ETFDH gene and the observed deficiency of a number of different mitochondrial dehydrogenases as well as deficiency of FAD and coenzyme Q(10). With SCAD deficiency, the challenge is to elucidate whether ACADS gene variations are disease-associated, especially when combined with other genetic/cellular/environmental factors, which may act synergistically.

The ACADS gene variation spectrum in 114 patients with short-chain acyl-CoA dehydrogenase (SCAD) deficiency is dominated by missense variations leading to protein misfolding at the cellular level

Short-chain acyl-CoA dehydrogenase (SCAD) deficiency is an inherited disorder of mitochondrial fatty acid oxidation associated with variations in the ACADS gene and variable clinical symptoms. In addition to rare ACADS inactivating variations, two common variations, c.511C > T (p.Arg171Trp) and c.625G > A (p.Gly209Ser), have been identified in patients, but these are also present in up to 14% of normal populations leading to questions of their clinical relevance. The common variant alleles encode proteins with nearly normal enzymatic activity at physiological conditions in vitro. SCAD enzyme function, however, is impaired at increased temperature and the tendency to misfold increases under conditions of cellular stress. The present study examines misfolding of variant SCAD proteins identified in patients with SCAD deficiency. Analysis of the ACADS gene in 114 patients revealed 29 variations, 26 missense, one start codon, and two stop codon variations. In vitro import studies of variant SCAD proteins in isolated mitochondria from SCAD deficient (SCAD-/-) mice demonstrated an increased tendency of the abnormal proteins to misfold and aggregate compared to the wild-type, a phenomenon that often leads to gain-of-function cellular phenotypes. However, no correlation was found between the clinical phenotype and the degree of SCAD dysfunction. We propose that SCAD deficiency should be considered as a disorder of protein folding that can lead to clinical disease in combination with other genetic and environmental factors.

Structural basis for substrate fatty acyl chain specificity: crystal structure of human very-long-chain acyl-CoA dehydrogenase

Very-long-chain acyl-CoA dehydrogenase (VLCAD) is a member of the family of acyl-CoA dehydrogenases (ACADs). Unlike the other ACADs, which are soluble homotetramers, VLCAD is a homodimer associated with the mitochondrial membrane. VLCAD also possesses an additional 180 residues in the C terminus that are not present in the other ACADs. We have determined the crystal structure of VLCAD complexed with myristoyl-CoA, obtained by co-crystallization, to 1.91-A resolution. The overall fold of the N-terminal approximately 400 residues of VLCAD is similar to that of the soluble ACADs including medium-chain acyl-CoA dehydrogenase (MCAD). The novel C-terminal domain forms an alpha-helical bundle that is positioned perpendicular to the two N-terminal helical domains. The fatty acyl moiety of the bound substrate/product is deeply imbedded inside the protein; however, the adenosine pyrophosphate portion of the C14-CoA ligand is disordered because of partial hydrolysis of the thioester bond and high mobility of the CoA moiety. The location of Glu-422 with respect to the C2-C3 of the bound ligand and FAD confirms Glu-422 to be the catalytic base. In MCAD, Gln-95 and Glu-99 form the base of the substrate binding cavity. In VLCAD, these residues are glycines (Gly-175 and Gly-178), allowing the binding channel to extend for an additional 12A and permitting substrate acyl chain lengths as long as 24 carbons to bind. VLCAD deficiency is among the more common defects of mitochondrial beta-oxidation and, if left undiagnosed, can be fatal. This structure allows us to gain insight into how a variant VLCAD genotype results in a clinical phenotype.

PPARs as therapeutic targets for correction of inborn mitochondrial fatty acid oxidation disorders

Enzyme defects in the mitochondrial fatty acid oxidation (FAO) are a large family of inherited metabolic disease well characterized clinically and genetically, but for which pharmacological strategies remain limited. It is now well established that regulation of genes involved in mitochondrial FAO is under control of the PPAR (peroxisome proliferator activated receptor) signalling pathway, and this led us to test a possible pharmacological correction of FAO disorders by fibrates and other PPAR activators. This review presents the basic data supporting our initial hypothesis, summarizes the results obtained in cells from patients with CPT II (carnitine palmitoyltransferase II) or VLCAD (very long-chain acyl-CoA dehydrogenase) deficiency, and discusses the perspectives and limits of this approach for therapy of these disorders.

Genetic basis for correction of very-long-chain acyl-coenzyme A dehydrogenase deficiency by bezafibrate in patient fibroblasts: toward a genotype-based therapy

Very-long-chain acyl-coenzyme A dehydrogenase (VLCAD) deficiency is an inborn mitochondrial fatty-acid beta-oxidation (FAO) defect associated with a broad mutational spectrum, with phenotypes ranging from fatal cardiopathy in infancy to adolescent-onset myopathy, and for which there is no established treatment. Recent data suggest that bezafibrate could improve the FAO capacities in beta-oxidation-deficient cells, by enhancing the residual level of mutant enzyme activity via gene-expression stimulation. Since VLCAD-deficient patients frequently harbor missense mutations with unpredictable effects on enzyme activity, we investigated the response to bezafibrate as a function of genotype in 33 VLCAD-deficient fibroblasts representing 45 different mutations. Treatment with bezafibrate (400 microM for 48 h) resulted in a marked increase in FAO capacities, often leading to restoration of normal values, for 21 genotypes that mainly corresponded to patients with the myopathic phenotype. In contrast, bezafibrate induced no changes in FAO for 11 genotypes corresponding to severe neonatal or infantile phenotypes. This pattern of response was not due to differential inductions of VLCAD messenger RNA, as shown by quantitative real-time polymerase chain reaction, but reflected variable increases in measured VLCAD residual enzyme activity in response to bezafibrate. Genotype cross-analysis allowed the identification of alleles carrying missense mutations, which could account for these different pharmacological profiles and, on this basis, led to the characterization of 9 mild and 11 severe missense mutations. Altogether, the responses to bezafibrate reflected the severity of the metabolic blockage in various genotypes, which appeared to be correlated with the phenotype, thus providing a new approach for analysis of genetic heterogeneity. Finally, this study emphasizes the potential of bezafibrate, a widely prescribed hypolipidemic drug, for the correction of VLCAD deficiency and exemplifies the integration of molecular information in a therapeutic strategy.

A newborn with VLCAD deficiency. Clinical, biochemical, and histopathological findings

Here we report a newborn with VLCAD deficiency with a severe neonatal onset type who presented with hypoglycemia, cardiomyopathy, mild hepatomegaly and slight hypoalbuminemia. The patient was also homozygous for a new missense mutation (R456H). Postmortem examination of the liver, heart and skeletal muscle revealed diffuse lipid accumulation in various amounts. Mild lobular and portal fibrosis as well as severe macrovesicular steatosis were also found in the liver. The fatal course of the patient may have resulted from diffuse lipid accumulation in the liver and myocardium, which probably began during the intrauterine life with slight hypoalbuminemia as a silent marker of this process.

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.

Expression and characterization of mutations in human very long-chain acyl-CoA dehydrogenase using a prokaryotic system

Very long-chain acyl-CoA dehydrogenase (VLCAD) catalyzes the first enzymatic step in the mitochondrial beta-oxidation of fatty acids 14-20 carbons in length. More than 100 cases of VLCAD deficiency have been reported with the disease varying from a severe, often fatal neonatal form to a mild adult-onset form. VLCAD is distinguished from matrix-soluble acyl-CoA dehydrogenases by its unique C-terminal domain, homodimeric structure, and localization to the inner mitochondrial membrane. We have for the first time expressed and purified VLCAD using a bacterial system. Recombinant VLCAD had similar biochemical properties to those reported for native VLCAD and the bacterial system was used to study six previously described disease-causing missense mutations including the two most common mild mutations (T220M, V243A), a mutation leading to the severe disease phenotype (R429W), and three mutations in the C-terminal domain (A450P, L462P, and R573W). Of particular interest was the finding that the A450P and L462P bacterial extracts had normal or increased amounts of VLCAD antigen and activity. In the pure form L462P had roughly 30% of wild-type activity while A450P was normal. Using computer modeling both mutations were mapped to a predicted charged surface of VLCAD that we postulate interacts with the mitochondrial membrane. In a membrane pull down assay both mutants showed greatly reduced mitochondrial membrane association, suggesting a mechanism for the disease in these patients. In summary, the bacterial expression system developed here will significantly advance our understanding of both the clinical aspects of VLCAD deficiency and the basic biochemistry of the enzyme.

Neonatal screening for very long-chain acyl-coA dehydrogenase deficiency: enzymatic and molecular evaluation of neonates with elevated C14:1-carnitine levels

OBJECTIVE

Neonatal screening programs for very long-chain acyl-coenzyme A dehydrogenase deficiency have been implemented recently in various countries. Mildly elevated C14:1-carnitine on day 3 of life strongly suggests very long-chain acyl-coenzyme A dehydrogenase deficiency.

DESIGN

We characterized 11 neonates with elevated C14:1-carnitine by enzyme and molecular analyses. Palmitoyl-coenzyme A oxidation was measured in lymphocytes. Sequencing of all 20 exons of the VLCAD gene was performed from genomic DNA.

RESULTS

Palmitoyl-coenzyme A oxidation revealed significantly decreased residual activities consistent with very long-chain acyl-coenzyme A dehydrogenase deficiency in 7 neonates. In 2 individuals, residual activities of 48% and 44%, respectively, suggested heterozygosity. Two disease-causing mutations were detected in 6 of 7 neonates with very long-chain acyl-coenzyme A dehydrogenase deficiency; in the remaining 1 patient, only 1 mutation was identified. Of 2 individuals with residual activities consistent with heterozygosity, 1 was heterozygous for a VLCAD mutation. The other child and both individuals with normal palmitoyl-coenzyme A oxidation had normal genotypes.

CONCLUSIONS

In 4 of 11 neonates identified with elevated C14:1-carnitine, very long-chain acyl-coenzyme A dehydrogenase deficiency was excluded. A C14:1-carnitine level > 1 micromol/L strongly suggests very long-chain acyl-coenzyme A dehydrogenase deficiency, whereas concentrations < or = 1 micromol/L do not allow a clear discrimination among affected patients, carriers, and healthy individuals. Further diagnostic evaluation, including enzyme and molecular analyses, is essential to identify very long-chain acyl-coenzyme A dehydrogenase deficiency correctly.

In vitro characterization and in vivo expression of human very-long chain acyl-CoA dehydrogenase

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is a disorder of fatty acid beta-oxidation that can present at any age with cardiomyopathy, rhabdomyolysis, hepatic dysfunction, and/or nonketotic hypoglycemia. Through the expansion of newborn screening programs an increasing number of individuals with VLCAD deficiency are being identified prior to the onset of symptoms allowing early initiation of therapy. The development of a safe, durable, and effective VLCAD gene delivery system for use at the time of diagnosis could result in a significant improvement in the quality and duration of life for patients with VLCAD deficiency. To this end, we developed a construct containing the human VLCAD cDNA under the control of the strong CMV promoter (pCMV-hVLCAD). A novel rabbit polyclonal anti-VLCAD antibody was prepared using a 24 amino-acid peptide unique to the human VLCAD protein to study human VLCAD expression in immune competent mice. Antibody specificity was demonstrated in Western blots of human VLCAD deficient fibroblasts and in pCMV-hVLCAD transiently transfected VLCAD deficient fibroblasts. Transfected fibroblasts showed correction of the metabolic block as demonstrated by normalization of C14- and C16-acylcarnitine species in cell culture media and restoration of VLCAD activity in cells. Following tail vein injection of pCMV-hVLCAD into mice, we demonstrated expression of hVLCAD in liver. Altogether, these steps are important in the development of a durable gene therapy for VLCAD deficiency.

Pitfalls of neonatal screening for very-long-chain acyl-CoA dehydrogenase deficiency using tandem mass spectrometry

Neonatal screening programs for very-long-chain acyl-CoA dehydrogenase deficiency (VLCADD) have recently been implemented. We report 2 newborns with elevated C14:1-carnitine levels on day 3 of life and normal levels on days 5 to 7. Enzyme and molecular analyses confirmed VLCADD in the first patient and heterozygosity in the second patient. We conclude that the diagnosis of VLCADD can be missed by acylcarnitine analysis during anabolic conditions. An increased C14:1-carnitine level can also occur in heterozygous individuals. Elevated C14:1-carnitine level on neonatal screening warrants further diagnostic workup even if a repeat sample demonstrates normal acylcarnitine levels.

VLCAD deficiency: pitfalls in newborn screening and confirmation of diagnosis by mutation analysis

We diagnosed six newborn babies with very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) through newborn screening in three years in Victoria (prevalence rate: 1:31,500). We identified seven known and two new mutations in our patients (2/6 homozygotes; 4/6 compound heterozygotes). Blood samples taken at age 48-72 h were diagnostic whereas repeat samples at an older age were normal in 4/6 babies. Urine analysis was normal in 5/5. We conclude that the timing of blood sampling for newborn screening is important and that it is important to perform mutation analysis to avoid false-negative diagnoses of VLCADD in asymptomatic newborn babies. In view of the emerging genotype-phenotype correlation in this disorder, the information derived from mutational analysis can be helpful in designing the appropriate follow-up and therapeutic regime for these patients.

Carnitine supplementation induces long-chain acylcarnitine production--studies in the VLCAD-deficient mouse

Carnitine supplementation does not affect carnitine concentrations in tissues of wild-type and very long-chain acyl-CoA dehydrogenase-deficient mice, but results in an increase in long-chain acylcarnitine production.

The effect of dantrolene sodium in Very Long Chain Acyl-CoA Dehydrogenase Deficiency

We present a patient, who experienced recurrent episodes of rhabdomyolysis. Her beneficial response to treatment with dantrolene sodium was previously reported. Adult onset Very Long Chain Acyl-CoA Dehydrogenase (VLCAD) deficiency has been diagnosed only recently. In adults, VLCAD deficiency results in recurrent fasting-, exercise-, or infection-induced muscle stiffness, muscle pain and myoglobinuria caused by rhabdomyolysis. This case illustrates for the first time the beneficial effect of dantrolene in VLCAD deficiency. We discuss the therapeutic mechanism of dantrolene sodium and its possible role as additional treatment modality for patients with VLCAD deficiency.

Abnormal mitochondrial bioenergetics and heart rate dysfunction in mice lacking very-long-chain acyl-CoA dehydrogenase

Mitochondrial very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is associated with severe hypoglycemia, cardiac dysfunction, and sudden death in neonates and children. Sudden death is common, but the underlying mechanisms are not fully understood. We report on a mouse model of VLCAD deficiency with a phenotype induced by the stresses of fasting and cold, which includes hypoglycemia, hypothermia, and severe bradycardia. The administration of glucose did not rescue the mice under stress conditions, but rewarming alone consistently led to heart rate recovery. Brown adipose tissue (BAT) from the VLCAD-/- mice showed elevated levels of the uncoupling protein isoforms and peroxisome proliferator-activated receptor-alpha. Biochemical assessment of the VLCAD(/- mice BAT showed increased oxygen consumption, attributed to uncoupled respiration in the absence of stress. ADP-stimulated respiration was 23.05 (SD 4.17) and 68.24 (SD 6.3) nmol O2.min(-1).mg mitochondrial protein(-1) for VLCAD+/+ and VLCAD-/- mice, respectively (P < 0.001), and carbonyl cyanide p-trifluoromethoxyphenylhydrazone-stimulated respiration was 35.9 (SD 3.6) and 49.3 (SD 9) nmol O2.min(-1).mg mitochondrial protein(-1) for VLCAD+/+ and VLCAD-/- mice, respectively (P < 0.20), but these rates were insufficient to protect them in the cold. We conclude that disturbed mitochondrial bioenergetics in BAT is a critical contributing factor for the cold sensitivity in VLCAD deficiency. Our observations provide insights into the possible mechanisms of stress-induced death in human newborns with abnormal fat metabolism and elucidate targeting of specific substrates for particular metabolic needs.

Bezafibrate increases very-long-chain acyl-CoA dehydrogenase protein and mRNA expression in deficient fibroblasts and is a potential therapy for fatty acid oxidation disorders

Inherited defect in very-long-chain acyl-CoA dehydrogenase (VLCAD), a mitochondrial enzyme catalyzing the initial step of long-chain fatty acid beta-oxidation (FAO), is one of the most frequent FAO enzyme defects. VLCAD deficiency is associated with clinical manifestations varying in severity, tissue involvement and age of onset. The molecular basis of VLCAD deficiency has been elucidated but therapeutic approaches are quite limited. In this study, we tested the hypothesis that fibrates, acting as agonist of peroxisome proliferator-activated receptors (PPARs), might stimulate FAO in VLCAD-deficient cells. We demonstrate that addition of bezafibrate or fenofibric acid in the culture medium induced a dose-dependent (up to 3-fold) increase in palmitate oxidation capacities in cells from patients with the myopathic form of VLCAD deficiency, but not in cells from severely affected patients. Complete normalization of cell FAO capacities could be achieved after exposure to 500 microm bezafibrate for 48 h. Cell therapy of VLCAD deficiency was related to drug-induced increases in VLCAD mRNA (+44 to +150%; P<0.001), protein (1.5-2-fold) and residual enzyme activity (up to 7.7-fold) in patient cells. Bezafibrate also diminished the production of toxic long-chain acylcarnitines by 90% in cells harboring moderate VLCAD deficiency. Finally, real-time PCR studies indicated that bezafibrate potentially stimulated gene expression of other enzymes in the beta-oxidation pathway. These data highlight the potential of fibrates in the correction of inborn FAO defects, as most mutations associated with these defects are compatible with the synthesis of a mutant protein with variable levels of residual enzyme activity.

Human acyl-CoA dehydrogenase-9 plays a novel role in the mitochondrial beta-oxidation of unsaturated fatty acids

Unsaturated fatty acids play an important role in the prevention of human diseases such as diabetes, obesity, cancer, and neurodegeneration. However, their oxidation in vivo by acyl-CoA dehydrogenases (ACADs) that catalyze the first step of each cycle of mitochondrial fatty acid beta-oxidation is not entirely understood. Recently, a novel ACAD (ACAD-9) of unknown function that is highly homologous to human very-long-chain acyl-CoA dehydrogenase was identified by large-scale random sequencing. To characterize its enzymatic role, we have expressed ACAD-9 in Escherichia coli, purified it, and determined its pattern of substrate utilization. The N terminus of the mature form of the enzyme was identified by in vitro mitochondrial import studies of precursor protein. A 37-amino acid leader peptide was cleaved sequentially by two mitochondrial peptidases to yield a predicted molecular mass of 65 kDa for the mature subunit. Submitochondrial fractionation studies found native ACAD-9 to be associated with the mitochondrial membrane. Gel filtration analysis indicated that, like very-long-chain acyl-CoA dehydrogenase, ACAD-9 is a dimer, in contrast to the other known ACADs, which are tetramers. Purified mature ACAD-9 had maximal activity with long-chain unsaturated acyl-CoAs as substrates (C16:1-, C18:1-, C18:2-, C22:6-CoA). These results suggest a previously unrecognized role for ACAD-9 in the mitochondrial beta-oxidation of long-chain unsaturated fatty acids. Because of the substrate specificity and abundance of ACAD-9 in brain, we speculate that it may play a role in the turnover of lipid membrane unsaturated fatty acids that are essential for membrane integrity and structure.

Long-chain fatty acid oxidation during early human development

Patients with very long-chain acyl-CoA dehydrogenase (VLCAD) and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD)/mitochondrial trifunctional protein (MTP) deficiency, disorders of the mitochondrial long-chain fatty acid oxidation, can present with hypoketotic hypoglycemia, rhabdomyolysis, and cardiomyopathy. In addition, patients with LCHAD/MTP deficiency may suffer from retinopathy and peripheral neuropathy. Until recently, there was no indication of intrauterine morbidity in these disorders. This observation was in line with the widely accepted view that fatty acid oxidation (FAO) does not play a significant role during fetal life. However, the high incidence of the gestational complications acute fatty liver of pregnancy and hemolysis, elevated liver enzymes, and low platelets syndrome observed in mothers carrying a LCHAD/MTP-deficient child and the recent reports of fetal hydrops due to cardiomyopathy in MTP deficiency, as well as the high incidence of intrauterine growth retardation in children with LCHAD/MTP deficiency, suggest that FAO may play an important role during fetal development. In this study, using in situ hybridization of the VLCAD and the LCHAD mRNA, we report on the expression of genes involved in the mitochondrial oxidation of long-chain fatty acids during early human development. Furthermore, we measured the enzymatic activity of the VLCAD, LCHAD, and carnitine palmitoyl-CoA transferase 2 (CPT2) enzymes in different human fetal tissues. Human embryos (at d 35 and 49 of development) and separate tissues (5-20 wk of development) were used. The results show a strong expression of VLCAD and LCHAD mRNA and a high enzymatic activity of VLCAD, LCHAD, and CPT2 in a number of tissues, such as liver and heart. In addition, high expression of LCHAD mRNA was observed in the neural retina and CNS. The observed pattern of expression during early human development is well in line with the spectrum of clinical signs and symptoms reported in patients with VLCAD or LCHAD/MTP deficiency.

Fuel utilization in patients with very long-chain acyl-coa dehydrogenase deficiency

Fuel utilization in two adult patients with the myopathic form of very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency and five healthy subjects was investigated with stable isotopes during exercise at 50% of VO2max. The findings indicate that residual VLCAD activity in the patients is sufficient to maintain normal oxidation of fat at rest, but that fat oxidation rate cannot increase above basal levels during exercise. This can cause an energy deficit and intramuscular accumulation of fat intermediates that may induce the exercise-induced symptoms.

Homozygosity for a severe novel medium-chain acyl-CoA dehydrogenase (MCAD) mutation IVS3-1G > C that leads to introduction of a premature termination codon by complete missplicing of the MCAD mRNA and is associated with phenotypic diversity ranging from sudden neonatal death to asymptomatic status

Virtually all patients with medium-chain acyl-CoA dehydrogenase deficiency (MCADD) are homozygous or compound heterozygous for the 985A > G mutation, which limits the study of a possible genotype/phenotype correlation. A newborn Palestinian infant died suddenly on the second day of life. A previous sibling had also died in similar circumstances aged 3 weeks. Urine organic acid and bloodspot acylcarnitine analysis were consistent with MCADD. He was homozygous for a novel MCAD splice mutation, IVS3-1G > C. This mutation leads to deletion of 7 bp and introduction of a premature termination codon as a result of complete missplicing of MCAD mRNA. This misspliced MCAD mRNA encodes a non-functional protein and is furthermore reduced in amounts due to nonsense-mediated decay, resulting in total lack of functional MCAD enzyme. This is the first molecular identification of MCADD in an Arab patient and the first reported splice mutation in the MCAD gene that has been functionally characterized. The association of homozygosity for a null mutation with lethal neonatal presentation in the index patient and presumably the previous infant suggested a genotype/phenotype correlation. However, a 6-year-old completely asymptomatic sibling also had the characteristic MCADD biochemical phenotype and was homozygous for the same IVS3-1G > C mutation. As a first candidate to modify the disease presentation, by modulating the overlapping enzyme activity, we tested the entire family for the prevalent SCAD gene 625G > A susceptibility variant. Interestingly, all family members were 625G > A homozygous. Additional genetic and/or environmental factors must play a major role in determining the phenotypic diversity of MCADD.

Implications of impaired ketogenesis in fatty acid oxidation disorders

Long-chain fatty acids are important sources of respiratory fuel for many tissues and during fasting the rate of hepatic production of ketone bodies is markedly increased. Many extra hepatic tissues utilize ketone bodies in the fasted state with the advantage that glucose is "spared" for more vital tissues like the brain. This glucose sparing effect of ketones is especially important in infants where there is a high proportional glucose utilization in cerebral tissue. The first reported inherited defect affecting fatty acid oxidation was described in 1973 and to date about 15 separate disorders have been described. Although individually rare, cumulatively fatty acid oxidation defects are relatively common, have major consequences for affected individuals and their families, and carry significant health care implications. The major biochemical consequence of fatty acid oxidation defects is an inability of extra hepatic tissues to utilize fatty acids as an energy source with absent or limited hepatic capacity to generate ketones. Clinically patients usually present in infancy with acute life-threatening hypoketotic hypoglycaemia, liver disease, hyperammonaemia and cerebral oedema, with or without cardiac involvement, usually following a period of catabolic stress. Chronically there may be muscle involvement with hypotonia or exercise intolerance with or without cardiomyopathy. Treatment is generally by the avoidance of fasting, frequent carbohydrate rich feeds and for long-chain defects, the replacement of long-chain dietary fats with medium-chain formulae. Novel approaches to treatment include the use of d,l-3-hydoxybutyrate or heptanoate as an alternative energy source.

Genetic defects in fatty acid beta-oxidation and acyl-CoA dehydrogenases. Molecular pathogenesis and genotype-phenotype relationships

Mitochondrial fatty acid oxidation deficiencies are due to genetic defects in enzymes of fatty acid beta-oxidation and transport proteins. Genetic defects have been identified in most of the genes where nearly all types of sequence variations (mutation types) have been associated with disease. In this paper, we will discuss the effects of the various types of sequence variations encountered and review current knowledge regarding the genotype-phenotype relationship, especially in patients with acyl-CoA dehydrogenase deficiencies where sufficient material exists for a meaningful discussion. Because mis-sense sequence variations are prevalent in these diseases, we will discuss the implications of these types of sequence variations on the processing and folding of mis-sense variant proteins. As the prevalent mis-sense variant K304E MCAD protein has been studied intensively, the investigations on biogenesis, stability and kinetic properties for this variant enzyme will be discussed in detail and used as a paradigm for the study of other mis-sense variant proteins. We conclude that the total effect of mis-sense sequence variations may comprise an invariable--sequence variation specific--effect on the catalytic parameters and a conditional effect, which is dependent on cellular, physiological and genetic factors other than the sequence variation itself.

Very-long-chain acyl-coenzyme a dehydrogenase deficiency in mice

Fatty acid oxidation (FAO) defects are inborn errors of metabolism clinically associated with cardiomyopathy and sudden infant death syndrome (SIDS). FAO disorders often present in infancy with myocardial dysfunction and arrhythmias after exposure to stresses such as fasting, exercise, or intercurrent viral illness. It is uncertain whether the heart, in the absence of stress, is normal. We generated very-long-chain acyl-coenzyme A dehydrogenase (VLCAD)-deficient mice by homologous recombination to define the onset and molecular mechanism of myocardial disease. We found that VLCAD-deficient hearts have microvesicular lipid accumulation, marked mitochondrial proliferation, and demonstrated facilitated induction of polymorphic ventricular tachycardia, without antecedent stress. The expression of acyl-CoA synthase (ACS1), adipophilin, activator protein 2, cytochrome c, and the peroxisome proliferator activated receptor gamma coactivator-1 were increased immediately after birth, preceding overt histological lipidosis, whereas ACS1 expression was markedly downregulated in the adult heart. We conclude that mice with VLCAD deficiency have altered expression of a variety of genes in the fatty acid metabolic pathway from birth, reflecting metabolic feedback circuits, with progression to ultrastructural and physiological correlates of the associated human disease in the absence of stress.

MS/MS-based newborn and family screening detects asymptomatic patients with very-long-chain acyl-CoA dehydrogenase deficiency

OBJECTIVES

To determine whether asymptomatic persons with biochemical evidence of very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency identified through expanded newborn screening with tandem mass spectometry have confirmed disease.

STUDY DESIGN

We characterized 8 asymptomatic VLCAD-deficient individuals by enzyme and/or mutational analysis and compared them with clinically diagnosed, symptomatic patients with regard to mutations, enzyme activity, phenotype, and age of disease onset.

RESULTS

VLCAD molecular analyses in 6 unrelated patients revealed the previously reported V243A mutation, associated with hepatic or myopathic phenotypes, on 7/12 alleles. All other mutations were also missense mutations. Residual VLCAD activities of 6% to 11% of normal were consistent with milder phenotypes. In these identified individuals treated prospectively with dietary modification as preventive measures, clinical symptoms did not develop during follow-up.

CONCLUSIONS

MS/MS-based newborn screening correctly identifies VLCAD-deficient individuals. Based on mutational and enzymatic findings, these infants probably are at risk of future disease. Because life-threatening metabolic derangement can occur even in otherwise mild phenotypes, we advocate universal newborn screening programs for VLCAD deficiency to detect affected patients and prevent development of metabolic crises. Longer-term follow-up is essential to define outcomes, the definite risk of future disease, and appropriate treatment recommendations.

Clear relationship between ETF/ETFDH genotype and phenotype in patients with multiple acyl-CoA dehydrogenation deficiency

Mutations in electron transfer flavoprotein (ETF) and its dehydrogenase (ETFDH) are the molecular basis of multiple acyl-CoA dehydrogenation deficiency (MADD), an autosomal recessively inherited and clinically heterogeneous disease that has been divided into three clinical forms: a neonatal-onset form with congenital anomalies (type I), a neonatal-onset form without congenital anomalies (type II), and a late-onset form (type III). To examine whether these different clinical forms could be explained by different ETF/ETFDH mutations that result in different levels of residual ETF/ETFDH enzyme activity, we have investigated the molecular genetic basis for disease development in nine patients representing the phenotypic spectrum of MADD. We report the genomic structures of the ETFA, ETFB, and ETFDH genes and the identification and characterization of seven novel and three previously reported disease-causing mutations. Our molecular genetic investigations of these nine patients are consistent with three clinical forms of MADD showing a clear relationship between the nature of the mutations and the severity of disease. Interestingly, our data suggest that homozygosity for two null mutations causes fetal development of congenital anomalies resulting in a type I disease phenotype. Even minute amounts of residual ETF/ETFDH activity seem to be sufficient to prevent embryonic development of congenital anomalies giving rise to type II disease. Overexpression studies of an ETFB-D128N missense mutation identified in a patient with type III disease showed that the residual activity of the mutant enzyme could be rescued up to 59% of that of wild-type activity when ETFB-D128N-transformed E. coli cells were grown at low temperature. This indicates that the effect of the ETF/ETFDH genotype in patients with milder forms of MADD, in whom residual enzyme activity allows modulation of the enzymatic phenotype, may be influenced by environmental factors like cellular temperature.

Molecular and phenotypic heterogeneity in mitochondrial trifunctional protein deficiency due to beta-subunit mutations

The mitochondrial trifunctional protein (TFP) is a multienzyme complex of the fatty acid beta-oxidation cycle. It is composed of four alpha-subunits (HADHA) harboring long-chain enoyl-CoA hydratase and long-chain L-3-hydroxyacyl-CoA dehydrogenase (LCHAD) and four beta-subunits (HADHB) harboring long-chain 3-ketoacyl-CoA thiolase (LKAT). Mutations in either subunit can result in TFP deficiency with reduced activity of all three TFP enzymes. We characterize 15 patients from 13 families with beta-subunit mutations by clinical, biochemical, and molecular features. Three clinical phenotypes are apparent: a severe neonatal presentation with cardiomyopathy, Reye-like symptoms, and early death (n=4); a hepatic form with recurrent hypoketotic hypoglycemia (n=2); and a milder later-onset neuromyopathic phenotype with episodic myoglobinuria (n=9). Maternal HELLP syndrome occurred in two mothers independently of the fetal phenotype. Mutational analysis revealed 16 different mutations, the majority being missense mutations (n=12). The predominance of missense mutations and the milder myopathic phenotype are consistent. Based upon homology to yeast thiolase that has been characterized structurally, the mutation localization within the protein correlates with the clinical phenotype. Outer loop mutations that are expected to alter protein stability less were only present in milder forms. The degree of reduction in thiolase antigen also correlated with the severity of clinical presentation. Although TFP deficiency is highly heterogeneous, there is genotype-phenotype correlation.

A young woman with persistent hypoglycemia, rhabdomyolysis, and coma: recognizing fatty acid oxidation defects in adults

OBJECTIVE

To describe an acutely decompensated adult patient with very-long-chain acyl-coenzyme A dehydrogenase (VLCAD) deficiency.

DESIGN

Case report.

SETTING

Medical intensive care unit of the University Hospital Hamburg-Eppendorf, Germany.

PATIENT

A 32-yr-old female comatose patient with persistent hypoglycemia, rhabdomyolysis, and acute cardiomyopathy after a prolonged history of recurrent muscular weakness.

INTERVENTIONS AND MEASUREMENTS

Treatment in the intensive care unit for 20 days. The combination of symptoms led to the detection of increased dicarboxylic acids in her urine and an abnormal profile of acylcarnitines in her blood. In cultured fibroblasts, the oxidation of palmitate, measured as the production of acetylcarnitine, was reduced. Direct measurement of VLCAD activity proved to be 30% of normal. DNA analysis showed two different mutations in the VLCAD gene of the patient.

RESULTS

The patient fully recovered.

CONCLUSIONS

Genetic defects of fatty acid oxidation should be suspected, even in previously healthy adults, when typical symptoms such as nonketotic hypoglycemia, rhabdomyolysis, cardiomyopathy, or unexplained organ steatosis point to such a disorder of energy metabolism.

Overlapping gene structure of human VLCAD and DLG4

Very-long-chain acyl-CoA dehydrogenase (VLCAD) is a major enzyme catalysing the first step in mitochondrial beta-oxidation of long-chain fatty acids. During analysis of the VLCAD promoter, we discovered that another gene, discs-large-related 4 (DLG4), overlaps VLCAD and is transcribed in the opposite direction. DLG4 encodes postsynaptic density-95 (PSD95) protein, which plays critical roles in the formation and maintenance of synaptic junctions. The transcription start site of the VLCAD gene was determined by primer extension analysis and the overlapping structure of VLCAD and DLG4 was clarified. VLCAD and DLG4 are arranged in a head-to-head orientation on chromosome 17p13, and share a 245 bp overlapping region that contains part of DLG4 exon 1 and the entire exon 1 of VLCAD including 62 bp of protein coding sequence. Despite the overlap of their 5' ends, DLG4 and VLCAD exhibit peak mRNA expression in different tissues, suggesting that they are independently regulated at the transcriptional level. Interestingly, VLCAD and DLG4 genes do not overlap in the mouse or Drosophila genomes.