Hypoglycemia, hypotonia, and cardiomyopathy: the evolving clinical picture of long-chain acyl-CoA dehydrogenase deficiency

Inherited defects in fatty acid oxidation, which have been described and diagnosed with increasing frequency in the last decade, are most commonly attributed to a deficiency in the activity of medium-chain acyl-CoA dehydrogenase. Few cases of the related enzyme defect of long-chain acyl-CoA dehydrogenase activity have been reported. An infant with documented long-chain acyl-CoA dehydrogenase deficiency is described with a detailed metabolic profile, long-term clinical follow-up, and response to treatment. This patient is compared with the seven previously published cases of this disorder in order to stress the unique features of the initial presentation, more subtle late manifestations of the disease, and clinical and biochemical differentiation from the more common medium-chain acyl-CoA dehydrogenase deficiency. This report stresses the enlarging spectrum of the clinical presentation and natural history of this defect in fatty acid oxidation.

Ca2+ responses to interleukin 1 and tumor necrosis factor in cultured human skin fibroblasts. Possible implications for Reye syndrome

Elevated concentrations of cytokines were found in the plasma of patients acutely ill with Reye syndrome (RS) but not in control subjects or recovered RS patients. To determine whether this disorder involves a genetically determined abnormal response to cytokines, the effects of tumor necrosis factor (TNF) and IL-1 on intracellular free Ca2+ were compared in cultured skin fibroblasts from control subjects and patients with RS. IL-1 and TNF caused rapid, transient, and concentration-dependent increases in cytosolic free Ca2+. The peak cytosolic free Ca2+ was greater and occurred at higher concentrations of IL-1 and TNF in patient cells than in cells from age-matched controls. In control cells, the Ca2+ transient diminished sharply with increasing amounts of IL-1 or TNF above the maximum stimulatory concentration. In contrast, in patient fibroblast this bell-shaped curve of concentration dependency was much less apparent. Bradykinin-stimulated Ca2+ transients were similar in the two groups and did not exhibit the bell-shaped concentration dependency. Thus, plasma cytokine levels are elevated in RS patients and the Ca2+ response to cytokines is increased in cells derived from these patients. We propose that the increased response reflects a genetic defect in cytokine receptor-modulated signal transduction.

Atypical riboflavin-responsive glutaric aciduria, and deficient peroxisomal glutaryl-CoA oxidase activity: a new peroxisomal disorder

Investigation of cultured skin fibroblasts in a patient with atypical riboflavin-responsive glutaric acidura revealed a marked deficiency of peroxisomal glutaryl-CoA oxidase. This is the first patient to be reported with glutaric aciduria caused by a peroxisomal rather than a mitochondrial dysfunction. This enzyme appears to be specific for glutaryl-CoA, as lauryl-CoA and dodecanedioyl-CoA oxidase activities in the fibroblasts were both normal. The urinary excretion of glutaric acid (0.5 mmol mmol creatinine-1) suggests that the flux through this pathway is considerably less than the mitochondrial flux through glutaryl-CoA dehydrogenase. The elevated glutaric acid excretion (to 0.8 mmol mmol creatinine-1) in response to lysine loading suggests that lysine is a precursor.

Early diagnosis and treatment of neonatal medium-chain acyl-CoA dehydrogenase deficiency: report of two siblings

Two siblings are reported who were symptomatic in the neonatal period. The first died suddenly at 4 days of age after regurgitating a meal. The postmortem examination showed steatosis of the liver, kidney and muscle. In the second, medium-chain acyl-CoA dehydrogenase (MCAD) deficiency was diagnosed at 3 days of age with muscular hypotonia, vomiting, hyperammonaemia and mild acidosis. Thus disorders of fatty acid oxidation should also be considered in newborns. The biochemical work up indicates that in neonates, analysis of serum medium-chain fatty acids and of acyl and free carnitine are more likely to lead to a diagnosis than determining dicarboxylic acids alone in urine. Long-term treatment was effective and monitored by the acyl/free carnitine ratio.

An acyl-coenzyme A dehydrogenase assay utilizing the ferricenium ion

A sensitive assay for medium chain acyl-CoA dehydrogenase has been developed by substituting ferricenium hexafluorophosphate for the physiological acceptor, electron transferring flavoprotein. The ferricenium ion is a facile oxidant of the octanoyl-CoA-reduced enzyme with a Vmax of 1400 min-1 and a KM of 55 microM at pH 7.6. The ferricenium assay does not require additional mediator dyes, exhibits low background rates, and avoids the necessity of purifying substantial amounts of electron transferring flavoprotein. Unlike the fluorescence-based electron transferring flavoprotein assay, this new procedure can be performed aerobically. Both assays give comparable results when tested with crude fibroblast homogenates from normal and medium chain acyl-CoA dehydrogenase deficient patients. The convenience of the ferricenium method suggests it may be generally useful as a screening assay for a number of acyl-CoA dehydrogenases.

Analysis of abnormal urinary metabolites in the newborn period in medium-chain acyl-CoA dehydrogenase deficiency

In order to determine which are useful early diagnostic markers for medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, we have analysed urine from an asymptomatic neonate. Profiling of urinary organic acids followed by peak confirmation by electron impact mass spectrometry revealed a high suberate/adipate ratio (greater than 1.0) and the presence of n-hexanoylglycine (HG). Acylcarnitine analysis by fast atom bombardment mass spectrometry (FAB-MS) was inconclusive, but FAB-MS/MS (tandem mass spectrometry) revealed diagnostic amounts of octanoylcarnitine and hexanoylcarnitine. Quantitative analysis of acylglycines by stable isotope dilution and chemical ionization mass spectrometry revealed a 30-fold increase in HG and increased suberylglycine, but no increase in 3-phenylpropionylglycine.

Medium-chain acyl-CoA dehydrogenase deficiency

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most frequently diagnosed defect in fatty acid metabolism and is one of the most common inborn errors of metabolism. Diagnosis may be difficult, since the disorder may present as hypoglycemia, sudden infant death syndrome or a Reye's syndrome-like illness. Because of the abrupt clinical deterioration seen with MCAD deficiency, as well as its treatable nature and its genetic implications, this disorder presents a significant challenge for family physicians.

Medium-chain acyl-CoA dehydrogenase deficiency. Diagnosis by stable-isotope dilution measurement of urinary n-hexanoylglycine and 3-phenylpropionylglycine

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, one of the most common inherited metabolic disorders, is often mistaken for the sudden infant death syndrome or Reye's syndrome. Diagnosing it has been difficult because of a lack of fast and reliable diagnostic methods. We developed a stable-isotope dilution method to measure urinary n-hexanoylglycine, 3-phenylpropionylglycine, and suberylglycine, and we retrospectively tested its accuracy in diagnosing MCAD deficiency. We measured the concentrations of these three acylglycines in 54 urine samples from 21 patients with confirmed MCAD deficiency during the acute and asymptomatic phases of the illness and compared the results with the concentrations in 98 samples from healthy controls and patient controls with various diseases. The levels of urinary hexanoylglycine and phenylpropionylglycine were significantly increased in all samples from the patients with MCAD deficiency, clearly distinguishing them from both groups of controls. Although urinary suberylglycine was increased in the patients, the range of values in the normal controls who were receiving formula containing medium-chain triglycerides was very wide, overlapping somewhat with the values in the patients with asymptomatic MCAD deficiency. These results indicate that the measurement of urinary hexanoylglycine and phenylpropionylglycine by our method is highly specific for the diagnosis of MCAD deficiency. The method is fast and can be applied to random urine specimens, without any pretreatment of patients.

Relationship between unusual hepatic acyl coenzyme A profiles and the pathogenesis of Reye syndrome

This study examines the relationship between impaired fatty acid oxidation and the pathogenesis of Reye syndrome. We present a hypothesis proposing that many clinical signs of this childhood disease are caused by accumulation of unusual acyl CoA esters, precursors to deacylated metabolites found in the patients' blood and urine. A new method was developed to measure acyl CoA compounds in small human liver biopsy samples, offering several advantages over previous techniques. A major finding was an accumulation in Reye syndrome patients of short- and medium-chain acyl CoA intermediates of fatty acid and branched-chain amino acid oxidation. These metabolites included octanoyl, isovaleryl, butyryl, isobutyryl, propionyl, and methylmalonyl CoA esters. The findings were explained in a model of hepatic fatty acid oxidation involving three interrelated pathways: mitochondrial beta-oxidation, peroxisomal beta-oxidation, and omega-oxidation in the endoplasmic reticulum. The results suggest that pathogenesis in Reye syndrome stems from generalized mitochondrial damage resulting in accumulation of acyl CoA esters. High levels of these compounds lead to inhibition of mitochondrial pathways for ureogenesis, gluconeogenesis, and fatty acid oxidation. The inhibited pathways, in turn, could cause the hyperammonemia, hypoglycemia, and hypoketonemia observed in patients. The model also explains underlying biochemical differences between patients with Reye syndrome and medium-chain acyl CoA dehydrogenase deficiency, another disorder of fatty acid metabolism. Acetyl CoA levels, in the latter disease, were dramatically decreased, compared with both human controls and Reye syndrome patients.

Decreased fasting free fatty acids with L-carnitine in children with carnitine deficiency

At the time of acute presentation, children with carnitine deficiency may have increased free fatty acid concentrations and hypoglycemia. However, whether carnitine replacement affects the plasma concentration of these substrates remains to be determined. Therefore, to evaluate the effect of carnitine replacement on plasma substrate and hormone concentrations, five children with carnitine deficiency (two idiopathic, two secondary to long-chain acyl coenzyme A dehydrogenase deficiency, one secondary to isovaleric acidemia) were fasted overnight before and after treatment with oral carnitine (80 +/- 7 mg.kg-1.day-1). During carnitine supplementation, plasma total carnitine (19 +/- 4 versus 45 +/- 6 nmol/ml, pretreatment versus treatment, respectively) and free carnitine (11 +/- 3 versus 31 +/- 6 nmol/ml), as well as red blood cell total carnitine (0.057 +/- 0.019 versus 0.130 +/- 0.019 nmol/mg of hemoglobin) increased (p less than 0.05). Fasting plasma glucose (83 +/- 4 versus 85 +/- 3 mg/dl) and ketone body (0.54 +/- 0.18 and 0.56 +/- 0.20 mM) concentrations did not change with carnitine supplementation, but plasma free fatty acids (1.28 +/- 0.32 versus 0.77 +/- 0.07 mM) decreased (p less than 0.05). No differences in fasting insulin, growth hormone, or cortisol concentrations were observed. Urinary excretion of free carnitine (0.1 +/- 0.0 versus 2.4 +/- 0.7 mumol/mg creatinine), total carnitine (0.3 +/- 0.1 versus 3.4 +/- 0.9 mumol/mg creatinine) and acyl carnitine (0.2 +/- 0.1 versus 0.9 +/- 0.3 mumol/mg creatinine) increased (p less than 0.05) with carnitine supplementation. The decreased plasma free fatty acid concentrations with carnitine supplementation may be due to more efficient fatty acid oxidation and/or increased urinary excretion of fatty acids as acylcarnitines.

Genetic deficiency of short-chain acyl-coenzyme A dehydrogenase in cultured fibroblasts from a patient with muscle carnitine deficiency and severe skeletal muscle weakness

Genetic deficiency of short-chain acyl-coenzyme A (CoA) dehydrogenase activity was demonstrated in cultured fibroblasts from a 2-yr-old female whose early postnatal life was complicated by poor feeding, emesis, and failure to thrive. She demonstrated progressive skeletal muscle weakness and developmental delay. Her plasma total carnitine level (35 nmol/ml) was low-normal, but was esterified to an abnormal degree (55% vs. control of less than 10%). Her skeletal muscle total carnitine level was low (7.6 nmol/mg protein vs. control of 14 +/- 2 nmol/mg protein) and was 75% esterified. Mild lipid deposition was noted in type I muscle fibers. Fibroblasts from this patient had 50% of control levels of acyl-CoA dehydrogenase activity towards butyryl-CoA as substrate at a concentration of 50 muM in a fluorometric assay based on the reduction of electron transfer flavoprotein. All of this residual activity was inhibited by an antibody against medium-chain acyl-CoA dehydrogenase. These data demonstrated that medium-chain acyl-CoA dehydrogenase accounted for 50% of the activity towards the short-chain substrate, butyryl-CoA, under these conditions, but that antibody against that enzyme could be used to unmask the specific and virtually complete deficiency of short-chain acyl-CoA dehydrogenase in this patient. Fibroblasts from her parents had intermediate levels of activity towards butyryl-CoA, consistent with the autosomal recessive inheritance of this metabolic defect.

Familial Reye-like syndrome: a presentation of medium-chain acyl-coenzyme A dehydrogenase deficiency

A 20-month-old girl with a family history of two siblings who died of an encephalopathy diagnosed as Reye syndrome presented to an emergency room in hypoglycemic coma and was found to have medium-chain acyl-coenzyme A dehydrogenase deficiency. The salient clinical and biochemical features of this newly described inborn error of fatty acid metabolism are described and contrasted to those of classical Reye syndrome. Important clues that should lead the clinician to suspect this disorder, methods of diagnosis, and appropriate acute and long-term therapy are also discussed.

Medium-chain and long-chain acyl CoA dehydrogenase deficiency: clinical, pathologic and ultrastructural differentiation from Reye's syndrome

The clinical and pathologic findings in 12 patients with medium-chain acyl CoA dehydrogenase deficiency and three patients with long-chain acyl CoA dehydrogenase deficiency are summarized. Although these inborn errors of intramitochondrial beta-oxidation of fatty acids present with similar findings to Reye's syndrome, there are clinical, laboratory and hepatic histologic differences. Younger age at presentation, history of unexplained sibling death, a previous episode of lethargy, hypoglycemia or acidosis precipitated by fasting stress and only mildly elevated serum transaminases with normal or only mildly prolonged prothrombin time may all suggest an acyl CoA dehydrogenase deficiency. Long-chain acyl CoA dehydrogenase deficiency is differentiated from medium-chain acyl CoA dehydrogenase deficiency by younger age at presentation, more profound cardiorespiratory depression, evidence of cardiomyopathy, and sequelae of muscle weakness, hypotonia and developmental delay. Definitive diagnosis is made by assay of medium-chain or long-chain enzyme activity in cultured skin fibroblasts or in leukocytes. Hepatic light microscopic alterations are essentially limited to steatosis, which may be either macro- or microvesicular. The cases with microvesicular steatosis can be differentiated morphologically from Reye's syndrome by electron microscopy, showing the absence of the mitochondrial changes characteristic of Reye's. Four of seven cases of acyl CoA dehydrogenase deficiency showed some variations from normal in the appearance of the hepatocyte mitochondria. The relationship of these variations to the basic metabolic defect(s) remains to be determined.

Biosynthesis of variant medium chain acyl-CoA dehydrogenase in cultured fibroblasts from patients with medium chain acyl-CoA dehydrogenase deficiency

We prepared monospecific antiserum in rabbits against medium chain acyl-CoA dehydrogenase (MCAD) purified from rat liver and studied the biosynthesis of MCAD in cultured skin fibroblasts from patients with MCAD deficiency using the antibody. Cells were incubated with [35S]methionine. The labeled MCAD was immunoprecipitated using the anti-rat MCAD antiserum and Staphylococcus aureus cells and then analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We first demonstrated that antirat MCAD antibody crossreacted specifically with human MCAD. In 13 MCAD-deficient cell lines tested, the residual MCAD activity ranged from 5-12% of the mean of normal controls, but the variant MCAD in all of these cells was indistinguishable from the normal human MCAD on the basis of molecular size, indicating that MCAD deficiency in all of these patients is most likely due to point mutation(s) in the MCAD gene.

Long-chain acyl coenzyme A dehydrogenase deficiency: an inherited cause of nonketotic hypoglycemia

Three children from unrelated families presented in early childhood with hypoglycemia and cardiorespiratory arrests associated with fasting. Significant hepatomegaly, cardiomegaly, and hypotonia were present at the time of initial presentation. Ketones were not present in the urine at the time of hypoglycemia in any patient; however, dicarboxylic aciduria was documented in one patient at the time of the acute episode and in two patients during fasting studies. Total plasma carnitine concentration was low with an increased esterified carnitine fraction. These findings suggested a defect in mitochondrial fatty acid oxidation, and specific assays were performed for the acyl coenzyme A (CoA) dehydrogenases. These analyses showed that the activity of the long-chain acyl CoA dehydrogenase was less than 10% of control values in fibroblasts, leukocytes, and liver tissue. Activities of the medium-chain, short-chain, and isovaleryl CoA dehydrogenases were not different from control values. With cultured fibroblasts, CO2 evolution from long-chain fatty acids was significantly reduced, while CO2 evolution from medium-chain and short-chain fatty acids was comparable to control values--findings consistent with a defect early in the beta-oxidation sequence. Studies of acyl CoA dehydrogenase activities in fibroblasts and leukocytes from parents of the patients showed levels of long-chain acyl CoA dehydrogenase activity intermediate between affected and control values and indicated an autosomal recessive form of inheritance of this enzymatic defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic deficiency of medium-chain acyl coenzyme A dehydrogenase: studies in cultured skin fibroblasts and peripheral mononuclear leukocytes

Medium-chain acyl coenzyme A (CoA) dehydrogenase deficiency was demonstrated in fibroblasts and/or mononuclear leukocytes from 14 patients, most of whom initially presented early in childhood with a Reye-like syndrome associated with hypoketotic hypoglycemia, dicarboxylic aciduria, and low levels of plasma carnitine. Parents of these patients had intermediate levels of medium-chain acyl CoA dehydrogenase activity, consistent with their being heterozygous for an autosomal recessive trait. All patients had normal levels of long-chain acyl CoA dehydrogenase activity, but had reduced short-chain acyl CoA dehydrogenase activity. Fatty acid oxidation was examined in cultured fibroblasts from five of the patients, using a series of 14C-labeled fatty acids of different chain length (palmitic, octanoic, and butyric). Oxidation of [1-14C]-octanoic acid was less than 20% of control levels: [1-14C], [6-14C]-, [16(14)C]-, and [14C(U)]-palmitic acid oxidation rates were 88, 51, 13, and 42% of control rates, respectively. [1-14C]-butyric acid was oxidized normally. These data extend our previous findings of medium-chain acyl CoA dehydrogenase deficiency in liver tissue from three of these patients. They demonstrate the value of cultured fibroblasts and leukocytes in the diagnosis and evaluation of inherited disorders of fatty acid oxidation.

Developmental changes in the adenine nucleotide translocase in the guinea pig

Investigations of developmental changes in energy metabolism in guinea pig liver mitochondria showed that mitochondria from the newborn were well coupled, with respiratory control ratios and membrane energy potentials similar to those obtained with mitochondria from the 1-day-old and the adult. In contrast, there was a 3-fold increase in the rate of mitochondrial respiration and a 2-fold increase in adenine nucleotide content during the first 24 h of extrauterine life. There was no significant change in the ATP/ADP ratio and only a 30% increase in the uncoupled rate of respiration during this same time period. Titrations of the adenine nucleotide translocase with the specific inhibitor, carboxyatractyloside, showed that the newborn had only 50% of the adenine nucleotide translocase activity of the adult. Furthermore, by applying flux control theory to these inhibitor titrations, it was possible to demonstrate that the adenine nucleotide translocase exerted greater control over respiration in the newborn than in the adult, and at maximal rates of coupled respiration the translocase had a control strength of 0.98. The consequences of this finding on cellular energy metabolism are discussed in relation to adaptation of the newborn to extrauterine life.

Medium-chain acyl-CoA dehydrogenase deficiency in children with non-ketotic hypoglycemia and low carnitine levels

Three children in two families presented in early childhood with episodes of illness associated with fasting which resembled Reye's syndrome: coma, hypoglycemia, hyperammonemia, and fatty liver. One child died with cerebral edema during an episode. Clinical studies revealed an absence of ketosis on fasting (plasma beta-hydroxybutyrate less than 0.4 mmole/liter) despite elevated levels of free fatty acids (2.6-4.2 mmole/liter) which suggested that hepatic fatty acid oxidation was impaired. Urinary dicarboxylic acids were elevated during illness or fasting. Total carnitine levels were low in plasma (18-25 mumole/liter), liver (200-500 nmole/g), and muscle (500-800 nmole/g); however, treatment with L-carnitine failed to correct the defect in ketogenesis. Studies on ketone production from fatty acid substrates by liver tissue in vitro showed normal rates from short-chain fatty acids, but very low rates from all medium and long-chain fatty acid substrates. These results suggested that the defect was in the mid-portion of the intramitochondrial beta-oxidation pathway at the medium-chain acyl-CoA dehydrogenase step. A new assay for the electron transfer flavoprotein-linked acyl-CoA dehydrogenases was used to test this hypothesis. This assay follows the decrease in electron transfer flavoprotein fluorescence as it is reduced by acyl-CoA-acyl-CoA dehydrogenase complex. Results with octanoyl-CoA as substrate indicated that patients had less than 2.5% normal activity of medium-chain acyl-CoA dehydrogenase. The activities of short-chain and isovaleryl acyl-CoA dehydrogenases were normal; the activity of long-chain acyl-CoA dehydrogenase was one-third normal. These results define a previously unrecognized inherited metabolic disorder of fatty acid oxidation due to deficiency of medium-chain acyl-CoA dehydrogenase.