Medium-chain acyl-CoA dehydrogenase deficiency in two siblings with a Reye-like syndrome

Medium-chain acyl-coenzyme A dehydrogenase deficiency: clinical course in 120 affected children

Medium-chain acyl-coenzyme A dehydrogenase deficiency is an autosomal recessive disorder of beta-oxidation of fatty acids manifested by episodic hypoglycemia, encephalopathy, apnea, and sudden death. Medical data were obtained on 120 patients with medium-chain acyl-coenzyme A dehydrogenase deficiency referred to Duke University Medical Center for biochemical testing. There were 55 male and 65 female subjects ranging from birth to 19 years of age; 118 subjects were white. Twenty-three children (19%) died before the diagnosis was made. Follow-up data were available in the 97 surviving patients for an average of 2.6 years after diagnosis. Psychodevelopmental data were collected on 73 patients older than 2 years of age. Unexpected morbidity included developmental and behavioral disability, chronic muscle weakness, failure to thrive, and cerebral palsy. We conclude that unidentified patients with this disorder have a significant risk of sudden death in early childhood and that survivors have a significant risk of developmental disability and chronic somatic illness.

Pathologic characterization of short-chain acyl-CoA dehydrogenase deficiency in BALB/cByJ mice

BALB/cByJ mice have a deficiency of short-chain acyl-CoA dehydrogenase (SCAD) and are a useful model for studying the inborn errors of fatty acid metabolism which affect humans. Patients with some of these disorders present with hypoglycemia, hyperammonemia, and microvesicular fatty change of hepatocytes. In the present study we examined pathogen-free, SCAD deficient BALB/cByJ mice and control BALB/cBy mice for biochemical and tissue changes following fasting or salicylate challenge. We observed mitochondrial swelling and microvesicular fatty changes in hepatocytes in mutant mice, especially severe following a fast. However, fasting did not alter their blood ammonia and there was no apparent clinical disease. Similarly, salicylates did not produce disease in the BALB/cByJ mice. We did detect in mice an alternative pathway for salicylate metabolism, by-passing glycine conjugation which is the principal metabolic pathway in humans.

A simple spectrophotometric assay for long-chain acyl-CoA dehydrogenase activity measurements in human skin fibroblasts

Long-chain acyl-CoA dehydrogenase (LCAD) deficiency is an autosomal recessive disorder of fatty acid metabolism characterized by hypoglycemia, muscle weakness and hepato- and cardiomegaly to varying extents. Analysis of organic acids in urine usually reveals dicarboxylic aciduria with elevated levels of adipic, suberic and sebacic acids as well as longer chain dicarboxylic acids. Correct diagnosis of suspected patients requires measurement of LCAD in tissue or preferably, white blood cells and/or cultured skin fibroblasts. In this paper we present a simple spectrophotometric enzyme assay based on the use of ferricenium hexafluorophosphate as electron acceptor. Under optimized conditions the method presented allowed unequivocal identification of LCAD-deficiency in fibroblast homogenates.

Hypoglycemia in infants

Because the infant's brain is to a large extent dependent on glucose utilization, hypoglycemia of infants can have grave effects on brain function, and it is important to diagnose it and, when possible, treat it promptly. Causes of hypoglycemia in infants are (a) excess insulin secretion, (b) factitious hyperinsulinemia, (c) GH or ACTH deficiency, (d) primary glucocorticoid deficiency, (e) defects of the enzymes involved in hepatic glucose production, or (f) defects in hepatic fatty acid oxidation.

Reye's syndrome in Olmsted County, Minnesota: did it exist before 1963?

In this study, our goals were to determine whether Reye's syndrome existed before the first published report of this entity in 1963 and to describe the long-term incidence and trend of this syndrome. Medical and pathologic records and pathologic specimens for Mayo Clinic patients, including those who were residents of Olmsted County, Minnesota, were reviewed through the facilities of the Rochester Epidemiology Project. On review, 12 cases were identified for the period 1920 through 1962; 2 of these cases were in Olmsted County residents. Of the 12 cases identified before 1963, 10 were in patients younger than 5 years of age. In addition to the aforementioned two cases, five others in Olmsted County were diagnosed between 1963 and 1989. Incidence rates were computed for the Olmsted County population. The number of cases and rates per 100,000 persons younger than 18 years of age in that population were 2 cases (0.3) for 1920 through 1962, 4 cases (0.7) for 1963 through 1980, and 1 case (0.4) for 1981 through 1989. Although cases found during the earlier periods may have included disorders that mimic Reye's syndrome, the recommended criteria from the Centers for Disease Control were applied to review of medical records and supported by pathologic findings in the liver. The data showed an age distribution tending toward young patients and no seasonality of occurrence. The incidence rates in Olmsted County, Minnesota, showed an increase for 1963 through 1980 over previous decades, followed by a decrease. The small numbers preclude any conclusion about trends in the incidence rates.

X-linked myotubular myopathy: a case report of prenatal and perinatal aspects

Nine families have been reported in which male newborns presented with X-linked myotubular (centronuclear) myopathy. Little is known about the biochemical basis of this disorder or about its natural history in utero. We report a family in which an infant with myotubular myopathy presented in utero with polyhydramnios, poor fetal movement, and fetal cardiac arrhythmias. Shortly after birth the infant died from severe respiratory insufficiency. Gas chromatography-mass spectrophotometry for serum organic acids showed a large octanoic acid peak, but total acyl-CoA dehydrogenase activities in liver were normal. The maternal family history was significant for two perinatal male deaths. Postmortem examination revealed generalized muscle wasting, cardiac enlargement, cryptorchidism, and flexion contractures. Examination of muscle showed numerous fibers that had enlarged, centrally located nuclei and perinuclear clear zones. The muscle fibers were hypotrophic and predominantly of type I. Biopsy specimens of the muscles of the mother and maternal aunt had increased numbers of centrally located nuclei. Neurologic examination was normal. The case demonstrates the typical clinical course, pathology, and family history of severe X-linked myotubular myopathy. In addition, it confirms the reported detection of fetal cardiac arrhythmias and documents what may be an abnormality in fatty acid oxidation.

Medium-chain acyl-CoA dehydrogenase deficiency: molecular aspects

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is an autosomal recessive disorder which is known to cause Reye-like syndrome in children and sudden infant death. A point mutation of lysine329-to-glutamic acid329 substitution in the MCAD gene was recently identified as the most common mutation in patients with MCAD deficiency. This mutation is responsible for about 90% of mutant MCAD alleles in Caucasians. Patients with this type of mutation have a variety of symptoms, indicating that the clinical heterogeneity of MCAD deficiency may not be caused entirely by genetic heterogeneity. Screening for the mutation among newborns in England, Australia, and United States of America indicates the prevalence of carriers to be 1 in 40-107, suggesting the high incidence of the mutation. Since presymptomatic diagnosis and appropriate dietary management are important in MCAD deficiency to prevent life-threatening complications, the relatively high incidence of this disorder may warrant population screening. The most common MCAD mutation can now be detected by DNA diagnostic methods using Guthrie cards. This makes it possible to screen a population efficiently for this potentially fatal disorder.

Structural organization and regulatory regions of the human medium-chain acyl-CoA dehydrogenase gene

Medium-chain acyl-CoA dehydrogenase (MCAD) is a highly regulated mitochondrial flavo-enzyme that catalyzes the initial reaction in fatty acid beta-oxidation. Deficiency of MCAD is a common inherited defect in energy metabolism. We have previously shown that the mRNA encoding MCAD in an MCAD-deficient child is homozygous for the point mutation A985 to G [Kelly et al. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 9236-9420]. To define the molecular basis of MCAD deficiency and as an initial step in the study of the regulation of MCAD gene expression, we determined the structure and organization of the human MCAD gene. The gene is comprised of 12 exons which span 44 kb of DNA. Comparison of the MCAD gene to MCAD mRNAs from the MCAD-deficient child revealed that missplicing was common, resulting in a variety of exon deletions and intron insertions. The MCAD gene promoter region is extremely GC-rich and lacks prototypical TATA and CAAT boxes. Several regions upstream of the promoter are homologous with mitochondrial enhancers purportedly involved in coordinate expression of nuclear genes encoding mitochondrial proteins. Transfection of chimeric plasmid constructs with 299 bp of upstream sequence into HepG2 cells revealed high-level transcriptional activity. We conclude that the precursor MCAD mRNA is misspliced to a high degree and complexity in association with the G985 mutation and the MCAD gene contains a strong promoter which shares some structural features with other "housekeeping" genes encoding mitochondrial proteins.

Medium chain acyl-CoA dehydrogenase deficiency

From 65 reported cases of medium chain acyl-CoA dehydrogenase deficiency, we found an average presenting age of 13.5 months and a mean age at death of 18.5 months. One quarter of patients died of a Reye-like syndrome and/or sudden infant death. In half the cases there had been at least one sibling death. Asymptomatic cases were not uncommon (12% of cases). The crises were generally induced by a prolonged fast and after a viral prodromal phase in three quarters of cases. The crises consisted of somnolence progressing to lethargy which could lead to coma. Vomiting was frequent (60% of cases). Seizures, which were found in 29% of cases, represented a bad prognosis. The physical examinations revealed frequently a variable and regressive anicteric hepatomegaly. Blood and urine analysis revealed in most instances hypoglycaemia (96% of cases) with hypoketonuria and sometimes metabolic acidosis. Hepatic and muscular cytolytic enzymes were frequently raised, as were plasma ammonia, urea, and uric acid. Plasma total or free carnitine concentrations, especially non-fasting, were diminished in most cases. Plasma saturated medium chain fatty acids and particularly unsaturated cis-4-decenoate were on the other hand raised during the crises or during fasting. Urinary organic acid analysis revealed a characteristic profile of medium chain aciduria: C6-C10 dicarboxylic acids, hydroxy acids, glycine conjugates, and carnitine conjugates. Oral loading tests with carnitine or phenylpropionate allow a precise diagnosis. The diagnosis is confirmed by specific assays in various tissues. Avoidance of prolonged fasting seems to be the mainstay of treatment.

Organic acidurias: a review. Part 1

Organic acidemias are disorders of intermediary metabolism that lead to accumulation of organic acids in biologic fluids, disturb acid-base balance, and derange intracellular biochemical pathways. Their clinical presentation reflects the resultant systemic disease and progressive encephalopathy. While in some organic acidemias, disturbed acid-base metabolism is the predominant presenting feature, in others it is less prominent or even absent. The etiologies of the more than 50 different phenotypes include impaired metabolism of branched-chain amino acids, vitamins, glucose, lipids, glutathione, and gamma-aminobutyric acid and defects of oxidative phosphorylation. Most organic acidemias present with neurologic manifestations, which include acutely or subacutely progressive encephalopathy that involves different parts of the nervous system. The age of presentation and the associated systemic, hematologic, and immune findings provide additional guidelines for differential diagnosis. We summarize major organic acidemias, while emphasizing their usual and unusual neurologic presentations.

Determination of medium chain acyl-CoA dehydrogenase activity in cultured skin fibroblasts using mass spectrometry

Medium chain acyl-CoA dehydrogenase deficiency, a defect of mitochondrial beta-oxidation, is one of the most frequently occurring among inborn errors of metabolism. We describe a rapid and sensitive gas chromatographic/mass spectrometric method allowing reliable assessment of medium chain acyl-CoA dehydrogenase activity in cultured skin fibroblasts. We investigated MCAD activity in three presumed medium chain acyl-CoA dehydrogenase deficient (MCADD) patients and 10 control subjects. The medium chain acyl-CoA dehydrogenase activity determined in three patients was 1.0 +/- 0.4 nmol.min-1.mg-1 protein (mean +/- SD; range: 0.6-1.4) and in controls it was 2.8 +/- 1.0 nmol.min-1.mg-1 protein (mean +/- SD; range: 1.6-4.4).

Is carnitine essential in children?

Carnitine has a fundamental biological role as a long-chain fatty acid carrier across the mitochondrial membrane and in ketone body formation. Although the body normally synthesizes carnitine, in certain circumstances such as total parenteral nutrition and haemodialysis a dietary supplement may be needed to maintain adequate levels. Several considerations suggest that carnitine is a truly essential nutrient in infancy and in other situations where the energy requirement is particularly high, e.g. pregnancy and breast feeding. There are, for example, congenital deficit syndromes due to enzymatic inadequacies. There is also the possible role of carnitine in serious metabolic disorders such as organic acidaemias and, above all, it has multiple physiological functions in major metabolic pathways which are essential for development and growth.

Interrelationships of liver and brain with special reference to Reye syndrome

Reye syndrome is an acute non-inflammatory encephalopathy that can be precipitated by toxic, infective, metabolic or hypoxic upsets. The biochemical changes point to mitochondrial dysfunction and this is substantiated by structural changes in mitochondria on electron microscopy. The toxic metabolites that accumulate are similar to those incriminated in hepatic encephalopathy and other metabolic diseases. These metabolites exert their deleterious effects by direct neuronal damage, neurotransmitter blockade, vascular damage, cerebral oedema, hypoxic ischaemic damage, demyelination, retardation of brain growth and neuronal storage. Brain capillary endothelial cells are very rich in mitochondria and mitochondrial disorders can effect the central nervous system primarily, and not just as a consequence of systemic metabolic upset.

Molecular characterization of inherited medium-chain acyl-CoA dehydrogenase deficiency

Deficiency of medium-chain acyl-CoA dehydrogenase (MCAD) is a common inherited defect in energy metabolism. Characterization of the mRNA encoding MCAD in a Dutch MCAD-deficient patient revealed an A----G change at nucleotide position 985 of the MCAD mRNA coding region. This point mutation results in the substitution of a glutamic acid for a lysine at amino acid position 304 of the mature protein. The single base change was not found in any wild-type MCAD mRNAs. A mutant allele-specific oligonucleotide probe was used in a hybridization analysis of amplified genomic DNA of MCAD-deficient family members, a carrier, and normal individuals. The hybridization analysis specifically identified individuals who were heterozygotes or homozygotes. In addition to the point mutation, a significant proportion of the index patient's MCAD mRNA contained a variety of deletions and insertions as a result of exon skipping and intron retention. The missplicing occurred in multiple regions throughout the MCAD mRNA. Analysis of the patient's MCAD gene in the regions where the missplicing occurred most frequently did not reveal a mutation in the splicing acceptor or donor sites. Therefore, the molecular characterization of this family revealed a crucial point mutation in the MCAD gene and an unusual abnormality in MCAD pre-mRNA splicing.

The high incidence of valproate hepatotoxicity in infants may relate to familial metabolic defects

The incidence of fatal hepatic failure associated with valproic acid (VPA) therapy is highest in children under the age of three years, particularly in those with developmental delay. The pathogenesis of VPA hepatotoxicity is unclear but may relate to the accumulation of a toxic metabolite of VPA which impairs fatty-acid oxidation. We describe two unrelated infants with developmental delay who developed hepatic failure while receiving VPA. Siblings of both children subsequently developed hepatic steatosis and intractable seizures without being exposed to VPA. This suggests that the two children who developed liver failure when receiving VPA may have had a familial metabolic disorder. Familial metabolic disorders may account partly for the higher incidence of fatal hepatotoxicity described in infants receiving VPA.

Mass spectrometric identification of 2-hydroxydodecanedioic acid and its homologues in urine from patients with hopantenate therapy during clinical episode

Urine from patients with calcium-4-(2,4-dihydroxy-3,3-dimethylbutyramido) butyrate hemihydrate (hopantenate) therapy during episodes of Reye's-like syndrome was found to contain a number of unusual dicarboxylic acids in high concentrations; odd- and even-numbered medium-chain dicarboxylic acids, alpha-hydroxydicarboxylic acids and beta-hydroxydicarboxylic acids. The abnormal excretion of dicarboxylic acids, alpha- and beta-hydroxydicarboxylic acids disappeared after discontinuance of hopantenate therapy. Besides the excretion of 2-hydroxydecandedioic acid, which has been previously described in Zellweger syndrome or neonatal adrenoleukodystrophy, a series of alpha-hydroxydicarboxylic acids was detected and identified. In this paper, we have characterized some new compounds by gas chromatography/mass spectrometry: 2-hydroxydodecanedioic acid, 2-hydroxydodecenedioic acid, 2-hydroxytetradecanedioic acid, 2-hydroxytetradecenedioic acid and 2-hydroxyoctanedioic acid.

Hypoglycemia: a pathophysiologic approach

An exploration of the factors that sustain glucose levels in the normal fasting subject reveals that the single major component is conservation of glucose rather than gluconeogenesis. Conservation is achieved by recycling of glucose carbon as lactate, pyruvate and alanine, and a profound decrease in the oxidation of glucose by the brain brought about by the provision and use of ketones. What glucose continues to be oxidized is for the most part formed from glycerol. Gluconeogenesis from protein plays little part in the process. Fasting hypoglycemia results from disorders affecting either one of the two critical sustaining factors--the recycling process or the availability and use of ketones. Individual hypoglycemic entities are examined against this background.

Inborn errors of amino acid and fatty acid metabolism with hypoglycemia as a major clinical manifestation

During the last decade it has become increasingly clear that severe hypoglycemia may be caused by specific enzymatic defects of amino acid and fatty acid metabolism. Several reports have presented hypoglycemic syndromes with reduced fatty acid transport or oxidation, decreased ketogenesis, or abnormalities of the Krebs cycle and electron transport chain. It is of particular interest that several enzymatic defects here discussed may present as Reye's syndrome. An intriguing fact is a highly variable clinical presentation, even in the presence of well-defined enzyme deficiencies. Some patients are desperately ill in the newborn period, whereas in other cases there are symptoms only during catabolic phases later in childhood. The presence of hypoglycemia may be related to low levels of acetyl CoA, with consequently reduced gluconeogenesis; alternatively the glucose-sparing effect of ketones is lost in states of reduced ketone body production. Treatment with pharmacological doses of vitamins may be attempted, depending upon the established or suspected diagnoses. With manifest hypoglycemia i.v. glucose infusion is the treatment of choice. By such means convulsions, and brain damage may be prevented.

Medium-chain acyl-CoA dehydrogenase deficiency: metabolic effects and therapeutic efficacy of long-term L-carnitine supplementation

Medium-chain acyl-CoA dehydrogenase deficiency is a recently described inborn error of metabolism characterized by episodes of coma and hypoketotic hypoglycaemia in response to prolonged fasting. Secondary carnitine deficiency has been documented in these patients as well as the excretion in the urine of medium-chain-length acyl carnitine esters, such as octanoylcarnitine. Based on the potential toxicity of medium-chain fatty acid metabolites and the beneficial responses of patients with other inborn errors of metabolism and secondary carnitine deficiency, oral carnitine has been proposed as treatment for children with medium-chain acyl-CoA dehydrogenase deficiency. We report the results of carefully monitored fasting challenges of an infant with this deficiency both before and after 3 months of oral carnitine therapy. Carnitine supplementation failed to prevent lethargy, vomiting, hypoglycaemia and accumulation of free fatty acids in response to fasting despite normalization of plasma carnitine levels and a marked increase in urinary excretion of acyl-carnitine esters. Potentially toxic medium-chain fatty acids accumulated in the plasma in spite of therapy. Based on this study of one patient, we stress that avoidance of fasting and prompt institution of glucose supplementation in situations when oral intake is interrupted remain the mainstays of therapy for medium-chain acyl-CoA dehydrogenase deficient patients.

Lipid storage myopathy associated with recurrent Reye syndrome-like attacks, but with a normal carnitine level

A 7-year-old girl developed recurrent episodes of hepatic and cerebral dysfunction which mimicked those in Reye syndrome (RS). Because of mild muscle weakness, she had repeated muscle biopsies which showed markedly increased amounts of lipid droplets, predominantly in type 1 fibers. Liver histological examination showed widespread hepatocellular steatosis. However, diffuse microvesicular fat, seen in RS, was not found in the cytoplasm. The concentrations of free- and acylcarnitine in serum and muscle were within normal ranges. Normal ketogenesis was induced by fasting. Based on the clinical, laboratory, and histopathological findings, our patient was initially thought to have systemic carnitine deficiency. However, the serum and muscle carnitine levels were within normal limits. Although the primary metabolic defect has yet to be elucidated, the present study indicates that lipid storage myopathy in the absence of carnitine deficiency can be complicated with RS-like episodes.

Neonatal onset of medium-chain acyl-CoA dehydrogenase deficiency in two siblings

Two male siblings with medium-chain acyl-CoA dehydrogenase deficiency were reported, in whom the enzyme activity was essentially undetectable and the symptoms and signs, including cyanosis, apnea, low body temperature, hypoglycemia and hyperammonemia, appeared within 48 hours of life. Muscle weakness and cardiomegaly in association with morphological abnormalities of mitochondria in skeletal and cardiac muscles, respectively, were found on electron microscopic examination in one of them. These observations suggest that the patients suffered from the most severe form of the disease, which has not been described in the literature.

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.

Nucleotide sequence of medium-chain acyl-CoA dehydrogenase mRNA and its expression in enzyme-deficient human tissue

Medium-chain acyl-CoA dehydrogenase (MCAD; acyl-CoA: (acceptor) 2,3-oxidoreductase, EC 1.3.99.3) is one of three similar enzymes that catalyze the initial step of fatty acid beta-oxidation. Definition of the primary structure of MCAD and the tissue distribution of its mRNA is of biochemical and clinical importance because of the recent recognition of inherited MCAD deficiency in humans. The MCAD mRNA nucleotide sequence was determined from two overlapping cDNA clones isolated from human liver and placental cDNA libraries, respectively. The MCAD mRNA includes a 1263-base-pair coding region and a 738-base-pair 3'-nontranslated region. A partial amino acid sequence (137 residues) determined on peptides derived from MCAD purified from porcine liver confirmed the identity of the cDNA clone. Comparison of the amino acid sequence predicted from the human MCAD cDNA with the partial protein sequence of the porcine MCAD revealed a high degree (88%) of interspecies sequence identity. RNA blot analysis shows that MCAD mRNA is expressed in a variety of rat (2.2 kilobases) and human (2.4 kilobases) tissues. Blot hybridization of RNA prepared from cultured skin fibroblasts from a patient with MCAD deficiency disclosed that mRNA was present and of similar size to MCAD mRNA derived from control fibroblasts. The isolation and characterization of MCAD cDNA is an important step in the definition of the defect underlying MCAD deficiency and in understanding its metabolic consequences.

The inborn errors of mitochondrial fatty acid oxidation

To date, seven inborn errors of mitochondrial fatty acid oxidation have been identified. A total of about 100 patients in the world have been reported. Clinically the beta-oxidation defects are more often characterized by episodic hypoglycaemia leading to a coma mimicking Reye's syndrome. The hypoglycaemia is non-ketotic since the synthesis of ketone bodies is deficient. Periods of decompensation occur when carbohydrate supply is poor, e.g. prolonged fasting, vomiting, or increased caloric requirements, as and when lipid stores are used. Defects in beta-oxidation have also been reported to be one cause of sudden infant death syndrome. The diagnosis of these inborn errors is by biochemical investigation since where symptoms suggest such a defect, the precise aetiology cannot be assessed. The biochemical diagnosis is based firstly on identification of abnormal plasma and of urinary metabolites during acute attacks. Derivatives of the omega-oxidation and omega-1-oxidation of medium chain fatty acids have been identified, as well as acylglycine and acylcarnitine conjugates. These metabolites are nearly always absent when patients are in good clinical condition. Secondly, the diagnosis must be based on the identification of the enzymatic defects: this involves global assays which allow a localization of the 'level' of the defect (i.e. the oxidation of long, medium or short chain fatty acids) and specific measurement of enzyme activities (acyl-CoA dehydrogenases and electron carriers: ETF and ETF-DH). The diagnosis of these disorders is of prime importance because of the severity of the clinical symptoms. These can be prevented, in some cases, by an appropriate diet (a high carbohydrate, low fat diet, sometimes supplemented with L-carnitine). In other cases, genetic counselling can be offered.

Molecular cloning of cDNAs encoding rat and human medium-chain acyl-CoA dehydrogenase and assignment of the gene to human chromosome 1

Rat liver mRNA encoding the precursor of medium-chain acyl-CoA dehydrogenase was purified to near homogeneity by polysome immunoadsorption using a polyclonal, monospecific antibody. A single-stranded, 32P-labeled cDNA probe was synthesized using the enriched mRNA as template and was used to screen directly 15,000 colonies from a total rat liver cDNA library constructed in pBR322. One clone [600 base pairs (bp)] was positively identified by hybrid-selected translation combined with mitochondrial processing of translated products. Using the isolated rat cDNA as probe, 43,000 colonies from a human liver cDNA library were screened. Three overlapping clones (1100 bp, 500 bp, and 400 bp) were isolated and positively identified by hybrid-selected translation. The largest human cDNA clone was subcloned into the transcription vector pGEM-2, which contains a bacteriophage T7 RNA polymerase promoter. In vitro transcription of this recombinant, followed by in vitro translation, showed that the cDNA clone coded for approximately 80% of the medium-chain acyl-CoA dehydrogenase protein. The sizes of rat and human mRNAs encoding the precursor of medium-chain acyl-CoA dehydrogenase were 2.2 and 2.4 kilobases long, respectively, as determined by blot hybridization analysis of electrophoretically fractionated poly(A)+ RNA. Southern blot analysis of DNAs from human-rodent somatic cell hybrids with an isolated human cDNA assigned the gene coding for this enzyme to the short arm of chromosome 1, band p31. The chromosomal assignment was confirmed by in situ hybridization of the probe to human metaphase cells. Direct screening of cDNA libraries using a highly enriched mRNA to generate a probe, as demonstrated in this study, may provide the most rapid and convenient approach to cDNA cloning of low-abundance mRNAs.

Serum dicarboxylic acids in patients with Reye syndrome

Reye syndrome resembles disorders of fatty acid metabolism. Analysis of serum free fatty acids from 18 patients with Reye syndrome revealed that dicarboxylic acids comprise as much as 55% (range 4% to 55%) of the patients' total free fatty acids; both medium- (6 to 12 carbon lengths) and long-chain (14 to 18 carbon lengths) dicarboxylic acids were identified. Long-chain dicarboxylic acids were not found in any control samples, whereas 86% +/- 4% of the serum dicarboxylic acids were long chain in 10 patients with Reye syndrome in state 3 to 4 coma and 31% +/- 8% in eight patients with a milder illness. The serum concentration of dicarboxylic acids correlated with the clinical state (P less than 0.001) and with the elevation in blood ammonia concentration (r2 = 0.8767). No long-chain dicarboxylic acids were found in the urine. The dicarboxylic acidemia in Reye syndrome may be secondary to the general mitochondrial dysfunction or could indicate that an insult to fatty acid metabolism or the stimulation of omega-oxidation is important in the pathogenesis of the illness. Measurement of serum dicarboxylic acids, especially long chain, may be important in assessing Reye syndrome and may prove useful in distinguishing this from other diseases.

Mass spectrometric identification of 2-hydroxy-sebacic acid in the urines of patients with neonatal adrenoleukodystrophy and Zellweger syndrome

The urines of children with neonatal adrenoleukodystrophy and Zellweger syndrome contained an excess of unusual even- and odd-numbered dicarboxylic acids with a chain length of from 5 to 15 carbon atoms, as well as 2-hydroxy-compounds, including 2-hydroxy-isocaproate, 2-hydroxy-glutarate and 2-hydroxy-sebacate. The latter product, not previously found in metabolic diseases, appears as an additional useful marker of these peroxisomal disorders.

Recognition of medium-chain acyl-CoA dehydrogenase deficiency in asymptomatic siblings of children dying of sudden infant death or Reye-like syndromes

The medium-chain acyl-CoA dehydrogenase (MCAD) deficiency of mitochondrial beta oxidation has been identified in two asymptomatic siblings in a family in which two previous deaths had been recorded, one attributed to sudden infant death syndrome and the other to Reye syndrome. Recognition of this disorder in one of the deceased and in the surviving siblings was accomplished by detection of a diagnostic metabolite, octanoylcarnitine, using a new mass spectrometric technique. This resulted in early treatment with L-carnitine supplement in the survivors, which should prevent metabolic deterioration. Further studies suggest that breast-feeding may be protective for infants with MCAD deficiency. Families with children who have had Reye syndrome or in which sudden infant death has occurred are at risk for MCAD deficiency. We suggest that survivors and asymptomatic siblings should be tested for this treatable disorder.