Plasma Acylcarnitine Research Articles

Hypoketotic Hypoglycemia with Myolysis and Hypoparathyroidism: An Unusual Association in Medium Chain Acyl-CoA Desydrogenase Deficiency (MCADD)

Medium-chain acyl-CoA deshydrogenase deficiency (MCADD) is the most frequent disorder of mitochondrial fatty acid oxidation (MFAO). We report a 3 year-old girl with enterovirus viremia who was referred after 36 hours of fasting with hypoketotic hypoglycemic coma and myolysis. Evolution was complicated by acute renal failure, increased serum levels of transaminases and hypoparathyroidism. Diagnosis of MCADD was supported by typical plasma acylcarnitine and urinary organic acid profiles, and confirmed by homozygosity for the common missense A985G mutation. Whereas myolysis is frequent in MFAO defects, it is rarely reported as a major accompanying sign in MCADD. Hypoparathyroidism has been previously reported in some MFAO deficiencies but has never been mentioned in association with MCADD. We review the possible mechanisms of hypoparathyroidism in MFAO deficiencies. Parathyroid glands and pancreas dysfunction should be screened in MFAO defects as these organs could be implicated in the clinical spectrum of the frequent A985G MCADD disease-causing mutation.

Hiperinsulinismo na infância: quando apenas uma dosagem de insulina não é suficiente

INTRODUCAO: A hipoglicemia em bebes e criancas pode causar convulsoes, atraso de desenvolvimento e dano cerebral permanente. O hiperinsulinismo (HI) e a causa mais comum de hipoglicemia, seja transitoria ou permanente. A HI e caracterizada pela secrecao inadequada de insulina, o que resulta em hipoglicemia persistente, de leve a grave. As diferentes formas de HI representam um grupo de doencas clinica, genetica e morfologicamente heterogeneo. CONTEUDO: Hiperinsulinismo congenito esta associado as mutacoes de SUR-1 e Kir6.2, glucoquinase, glutamato desidrogenase, 3-hidroxiacil-CoA desidrogenase de cadeia curta e expressao ectopica de SLC16A1 na membrana plasmatica das celulas beta. O HI pode estar associado ao estresse perinatal, como asfixia do nascimento, toxemia materna, prematuridade ou retardo do crescimento intra-uterino, resultando em hipoglicemia neonatal prolongada. Mimetismo de HI neonatal inclui pan-hipopituitarismo, hipoglicemia induzida por farmaco, insulinoma, anticorpos antiinsulina e estimuladores do receptor de insulina, sindrome de Beckwith-Wiedemann e disturbios congenitos de glicosilacao. Exames laboratoriais para HI podem incluir quantificacao de glicose, insulina, β-hidroxibutirato, acidos graxos, amonia e perfil de acilcarnitinas plasmaticos, alem de acidos orgânicos urinarios. Os exames geneticos estao disponiveis em laboratorios comerciais para os genes sabidamente associados a hiperinsulinemia. Testes de resposta insulinica aguda (RIA) sao uteis na caracterizacao fenotipica. Exames de imagem e histologicos tambem estao disponiveis para diagnosticar e classificar o HI. O objetivo do tratamento de criancas com HI e prevenir os danos cerebrais da hipoglicemia, mantendo niveis de glicose plasmatica acima de 70mg/dl por terapia farmacologica ou cirurgica. CONCLUSAO:A terapeutica do HI requer abordagem multidisciplinar que inclui endocrinologistas pediatricos, radiologistas, cirurgioes e patologistas, os quais sao treinados para diagnosticar, identificar e tratar o hiperinsulinismo.

Plasma acylcarnitine and fatty acid profiles during exercise and training in Standardbreds

To evaluate alterations in skeletal muscle carnitine metabolism during exercise and training by measuring changes in plasma acylcarnitine concentrations in Standardbreds. 10 Standardbred geldings with a mean +/- SD age of 20 +/- 2 months and weight of 384 +/- 42 kg. In a 32-week longitudinal study, training on a treadmill was divided into 4 phases as follows: phase 1, acclimatization for 4 weeks; phase 2, 18 weeks with alternating endurance and high-intensity exercise training; phase 3, increased training volume and intensity for another 6 weeks; and phase 4, deconditioning for 4 weeks. In phase 3, horses were randomly assigned to 2 groups as follows: control horses (which continued training at the same level as in phase 2) and high-intensity exercise trained horses. At the end of each phase, a standardized exercise test (SET) was performed. Plasma acylcarnitine, fatty acids, and lactic acid and serum beta-hydroxybutyric acid (BHBA) concentrations were assessed before and at different time points after each SET. Plasma lactic acid, total nonesterified fatty acids, 3-hydroxyisobutyric acid, and acetylcarnitine (C2-carnitine) concentrations significantly increased during SETs, whereas serum BHBA, plasma propionylcarnitine (C3-carnitine), and plasma butyryl- and isobutyrylcarnitine (C4-carnitine) concentrations decreased significantly, compared with those before SETs. Our findings indicated that the plasma acylcarnitine profile in horses likely reflects skeletal muscle carnitine metabolism following exercise, thereby providing a possible practical method to investigate potential disorders in carnitine metabolism in horses with myopathy.

Liquid chromatography/mass spectrometry determination of endogenous plasma acetyl and palmitoyl carnitines as potential biomarkers of β‐oxidation in mice

A robust bioanalytical method capable of measuring acetyl and palmitoyl carnitines was developed and validated. Application of hydrophilic interaction chromatography (HILIC) enabled retention of these highly polar and difficult to analyze compounds on a silica HPLC column. The chromatography was conducted with a high percentage of an organic component in the mobile phase, allowing high sensitivity for the pre-existing positively charged quaternary ammonium ions by electrospray ionization mass spectrometry. Successful application of the method to reliably quantify naturally occurring acyl carnitines in mouse plasma depended on the use of corresponding deuterated analogues. The specificity of the method, achieved through the use of stable isotope labeled compounds in combination with a mass spectral multiple reaction monitoring technique, permitted a non-invasive assessment of the overall change in the levels of these acyl carnitines in the plasma of intact animals administered peroxisome proliferator activated receptor (PPAR) agents. These acyl carnitines, as carriers of the corresponding long-chain fatty acids for transport into mitochondria, can be employed as potential biomarkers for significant alteration in the beta-oxidation process in an intact animal.

Importancia del diagnóstico precoz y el tratamiento temprano en el pronóstico de la aciduria glutárica tipo I

Glutaric Acidaemia type I (GA-I) is an autosomal recessive progressive neurodegenerative inborn error of metabolism caused by deficient activity of the enzyme glutaryl-CoA dehydrogenase (GCDH). In most cases, the diagnosis is established biochemically by the detection of glutaric acid and 3-hydroxy glutaric acid in urine and glutarylcarnitine in plasma. Patients excreting small amounts of glutaric acid may be overlooked. To investigate the value of expanded newborn screening by adding the measurement of urine glutarylcarnitine to conventional chromatography-mass spectrometry (GC-MS) in the diagnosis of GA-1. We report clinical and biochemical data in 5 GA-I patients diagnosed in our Hospital. Details regarding biochemical diagnosis are emphasised and the absence or presence of symptoms was correlated with neuroimaging findings, age at diagnosis and treatment. Two patients showed high glutarylcarnitine levels in plasma and were identified by routine newborn GC-MS screening. Following early appropriate treatment they are asymptomatic 6 years later. Two patients with delayed diagnosis displayed neurological sequels in spite of treatment. The remaining patient, who presented with encephalopathic episode at age 8 months showed normal glutarylcarnitine levels in routine plasma GC-MS but high urine glutarylcarnitine levels in a retrospectively screened urine sample from the newborn period. Early treatment seems to positively influence the clinical evolution of GA-I patients. Thus, improving the identification of GA-I represents an important diagnostic challenge. The urinary excretion of glutarylcarnitine is a specific biochemical marker of GA-I and allows the identification of patients without glutaric aciduria and with normal plasma acylcarnitine profiles.

Application of Metabolomic Principles to Disorders of Nucleotide Metabolism Reveals New Metabolic Perturbations

A metabolomic analysis of plasma amino acids and acylcarnitines was applied to four disorders of nucleotide metabolism. Multivariate analysis gave score plots that show segregation of hypoxanthine phosphoribosyltransferase and adenine phosphoribosyltransferase deficient plasma from controls with equivocal results for adenosine deaminase and dihydropyrimidine dehydrogenase deficiencies. Loadings plots revealed the principal metabolites responsible for the discrimination between these classes. There were increases for HPRT in C4-, C6-, and C3-DC (malonyl)-carnitines, and decreased serine. For APRT there were increases in C4- to C10- and C3-DC to C6-DC-carnitines, urea, 1-methylhistidine, 3-methylhistidine, and decreased tryptophan. For ADA deficiency there were increases in C4- and C6-carnitines, taurine, and isoleucine.

Interstitial deletion of 1p22.2p31.1 and medium‐chain acyl‐CoA dehydrogenase deficiency in a patient with global developmental delay

We report on a 6-year-old girl who presented at 6 months of age with seizures, delayed psychomotor development and mild facial dysmorphism. A small muscular ventricular septal defect was documented on echocardiogram and brain MRI showed a frontal brain anomaly. Urine organic acid analysis revealed dicarboxylic aciduria, and plasma acylcarnitine analysis showed marked elevation of octanoyl (C8) and decanoyl (C10) carnitines with C8:C10 ratio of 9:1. These results were indicative of medium chain acyl-CoA dehydrogenase deficiency. ACADM gene sequencing showed an apparent homozygous c.166G > C (Ala31Pro) missense mutation in exon 3; however, only the mother was found to be a carrier of this novel missense mutation. This finding along with non-regressive developmental delay prompted further karyotype and genomic investigations. An interstitial deletion of chromosome 1 was detected by repeat G-banding: 46,XX,del(1)(p22.2p31.1). Parental karyotypes were normal. The deletion was characterized by array CGH analysis using a 1 Mb BAC/PAC array platform. Clones deleted extended from RP11-88B10 (1p31.1) to RP5-1007M22 (1p22.2), a 15.5 Mb deletion which includes the ACADM locus. Clinical review of 6/7 cases of interstitial deletions with breakpoints of 1p22 and 1p31/32, including the patient in this report, indicate a variable phenotype. Thus, although G-band breakpoints are similar, common breakpoints for these alterations are unlikely. This is the first report of a patient with fatty acid oxidation defect caused by a mutation in combination with an interstitial chromosomal deletion.

Maternal glutaric acidemia, type I identified by newborn screening

We report two women with glutaric acidemia type I in whom the diagnosis was unsuspected until a low carnitine level was found in their newborn children. Both mothers had low carnitine in plasma. In the first, organic acid analysis was only done after fibroblast studies revealed normal carnitine uptake. Having learned from the first family, organic acid analysis was done immediately in the mother of family 2. In both, the plasma acylcarnitine profile was normal but both excreted the metabolites typical of their disorder. One of the women was a compound heterozygote for distinct mutations in the glutaric acid dehydrogenase gene, whereas the second was either homozygous or hemizygous for a mutation in Exon 6 of the gene.

Comprehensive plasma acylcarnitine profiles of type 2 diabetic and non‐diabetic subjects with or without an uncoupling protein 3 (UCP3) missense polymorphism

Type 2 diabetes mellitus (T2DM) is often correlated with reduced muscle fatty acid combustion in the fasted state. This may be due to dysfunctional mitochondrial activity and accumulation of specific lipid metabolites implicated in insulin resistance. Biomarkers of muscle fat combustion would be valuable to identify persons at‐risk for developing T2DM and to better understand muscle intermediary metabolism. To address this, we compared >40 individual plasma acylcarnitines in overnight‐fasted adult women harboring a UCP3 premature‐stop allele (50% lower whole‐body fat combustion, apparently due to limited muscle UCP3 activity) to a control cohort. Contrary to expectations, acylcarnitine profiles did not differ by genotype. However, across genotypes, T2DM subjects (n=44) displayed (relative to non‐diabetics, n=12): ~50% increased total acylcarnitines (6.52 ± 0.32 vs. 4.40 ± 0.55 μM; p<0.01), ~60% higher acetylcarnitine (5.35 ± 0.29 vs. 3.40 ± 0.46 μ p<0.01), and ~37% decreased propionylcarnitine (0.24 ± 0.02 vs. 0.38 ± 0.04 μ p<0.001). Such patterns are consistent with a hypothetical model in which fasted T2DM tissues (a) have inordinately low availability of propionyl‐CoA (a component of TCA cycle‐replenishing [anaplerotic] reactions), and (b) increased pools of pyruvate‐derived acetyl‐CoA, presumably due to relatively elevated glycolysis and/or reduced TCA cycle acetyl‐CoA consumption.

Hyperinsulinism in Infancy and Childhood: When an Insulin Level Is Not Always Enough

Hypoglycemia in infants and children can lead to seizures, developmental delay, and permanent brain damage. Hyperinsulinism (HI) is the most common cause of both transient and permanent disorders of hypoglycemia. HI is characterized by dysregulated insulin secretion, which results in persistent mild to severe hypoglycemia. The various forms of HI represent a group of clinically, genetically, and morphologically heterogeneous disorders. Congenital hyperinsulinism is associated with mutations of SUR-1 and Kir6.2, glucokinase, glutamate dehydrogenase, short-chain 3-hydroxyacyl-CoA dehydrogenase, and ectopic expression on beta-cell plasma membrane of SLC16A1. Hyperinsulinism can be associated with perinatal stress such as birth asphyxia, maternal toxemia, prematurity, or intrauterine growth retardation, resulting in prolonged neonatal hypoglycemia. Mimickers of hyperinsulinism include neonatal panhypopituitarism, drug-induced hypoglycemia, insulinoma, antiinsulin and insulin-receptor stimulating antibodies, Beckwith-Wiedemann Syndrome, and congenital disorders of glycosylation. Laboratory testing for hyperinsulinism may include quantification of blood glucose, plasma insulin, plasma beta-hydroxybutyrate, plasma fatty acids, plasma ammonia, plasma acylcarnitine profile, and urine organic acids. Genetic testing is available through commercial laboratories for genes known to be associated with hyperinsulinism. Acute insulin response (AIR) tests are useful in phenotypic characterization. Imaging and histologic tools are also available for diagnosing and classifying hyperinsulinism. The goal of treatment in infants with hyperinsulinism is to prevent brain damage from hypoglycemia by maintaining plasma glucose levels above 700 mg/L (70 mg/dL) through pharmacologic or surgical therapy. The management of hyperinsulinism requires a multidisciplinary approach that includes pediatric endocrinologists, radiologists, surgeons, and pathologists who are trained in diagnosing, identifying, and treating hyperinsulinism.

Deleterious Mutation in the Mitochondrial Arginyl–Transfer RNA Synthetase Gene Is Associated with Pontocerebellar Hypoplasia

Homozygosity mapping was performed in a consanguineous Sephardic Jewish family with three patients who presented with severe infantile encephalopathy associated with pontocerebellar hypoplasia and multiple mitochondrial respiratory-chain defects. This resulted in the identification of an intronic mutation in RARS2, the gene encoding mitochondrial arginine-transfer RNA (tRNA) synthetase. The mutation was associated with the production of an abnormally short RARS2 transcript and a marked reduction of the mitochondrial tRNA(Arg) transcript in the patients' fibroblasts. We speculate that missplicing mutations in mitochondrial aminoacyl-tRNA synthethase genes preferentially affect the brain because of a tissue-specific vulnerability of the splicing machinery.

Transient multiple acyl-CoA dehydrogenation deficiency in a newborn female caused by maternal riboflavin deficiency

A newborn female presented on the first day of life with clinical and biochemical findings consistent with multiple acyl-CoA dehydrogenase deficiency (MADD). Riboflavin supplementation corrected the biochemical abnormalities 24 h after commencing the vitamin. In vitro acylcarnitine profiling in intact fibroblasts both in normal and riboflavin depleted media showed normal oxidation of fatty acids excluding defects in electron transfer flavoprotein (ETF), or ETF ubiquinone oxidoreductase (ETF:QO), or a genetic abnormality in flavin metabolism. In addition, sequencing of the genes encoding ETF and ETF:QO in the proband did not reveal any pathogenic mutations. Determination of the maternal riboflavin status after delivery showed that the mother was riboflavin deficient. Repeat testing done two years after the infant’s birth and while on a normal diet showed that the mother was persistently riboflavin deficient and showed a typical MADD profile on plasma acylcarnitine testing. A possible genetic defect in riboflavin transport of metabolism in the mother is postulated to be the cause of the transient MADD seen in the infant. Sequencing of the SLC16A12, RFK and FLAD1 genes encoding key enzymes in riboflavin transport of metabolism in the mother did not identify any pathogenic mutations. The underlying molecular basis of the mother’s defect in riboflavin metabolism remains to be established.

Equine biochemical multiple acyl-CoA dehydrogenase deficiency (MADD) as a cause of rhabdomyolysis

Two horses (a 7-year-old Groninger warmblood gelding and a six-month-old Trakehner mare) with pathologically confirmed rhabdomyolysis were diagnosed as suffering from multiple acyl-CoA dehydrogenase deficiency (MADD). This disorder has not been recognised in animals before. Clinical signs of both horses were a stiff, insecure gait, myoglobinuria, and finally recumbency. Urine, plasma, and muscle tissues were investigated. Analysis of plasma showed hyperglycemia, lactic acidemia, increased activity of muscle enzymes (ASAT, LDH, CK), and impaired kidney function (increased urea and creatinine). The most remarkable findings of organic acids in urine of both horses were increased lactic acid, ethylmalonic acid (EMA), 2-methylsuccinic acid, butyrylglycine (iso)valerylglycine, and hexanoylglycine. EMA was also increased in plasma of both animals. Furthermore, the profile of acylcarnitines in plasma from both animals showed a substantial elevation of C4-, C5-, C6-, C8-, and C5-DC-carnitine. Concentrations of acylcarnitines in urine of both animals revealed increased excretions of C2-, C3-, C4-, C5-, C6-, C5-OH-, C8-, C10:1-, C10-, and C5-DC-carnitine. In addition, concentrations of free carnitine were also increased. Quantitative biochemical measurement of enzyme activities in muscle tissue showed deficiencies of short-chain acyl-CoA dehydrogenase (SCAD), medium-chain acyl-CoA dehydrogenase (MCAD), and isovaleryl-CoA dehydrogenase (IVD) also indicating MADD. Histology revealed extensive rhabdomyolysis with microvesicular lipidosis predominantly in type 1 muscle fibers and mitochondrial damage. However, the ETF and ETF-QO activities were within normal limits indicating the metabolic disorder to be acquired rather than inherited. To our knowledge, these are the first cases of biochemical MADD reported in equine medicine.

Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency

PurposeIsobutyryl-CoA dehydrogenase deficiency is a defect in valine metabolism and was first reported in a child with cardiomyopathy, anemia, and secondary carnitine deficiency. We identified 13 isobutyryl-CoA dehydrogenase–deficient patients through newborn screening due to an elevation of C4-acylcarnitine in dried blood spots. Because C4-acylcarnitine represents both isobutyryl- and butyrylcarnitine, elevations are not specific for isobutyryl-CoA dehydrogenase deficiency but are also observed in short-chain acyl-CoA dehydrogenase deficiency. To delineate the correct diagnosis, we have developed a follow-up algorithm for abnormal C4-acylcarnitine newborn screening results based on the comparison of biomarkers for both conditions. MethodsFibroblast cultures were established from infants with C4-acylcarnitine elevations, and the analysis of in vitro acylcarnitine profiles provided confirmation of either isobutyryl-CoA dehydrogenase or short-chain acyl-CoA dehydrogenase deficiency. Isobutyryl-CoA dehydrogenase deficiency was further confirmed by molecular genetic analysis of the gene encoding isobutyryl-CoA dehydrogenase (ACAD8). Plasma acylcarnitines, urine acylglycines, organic acids, and urine acylcarnitine results were compared between isobutyryl-CoA dehydrogenase– and short-chain acyl-CoA dehydrogenase–deficient patients. ResultsQuantification of C4-acylcarnitine in plasma and urine as well as ethylmalonic acid in urine allows the differentiation of isobutyryl-CoA dehydrogenase–deficient from short-chain acyl-CoA dehydrogenase–deficient cases. In nine unrelated patients with isobutyryl-CoA dehydrogenase deficiency, 10 missense mutations were identified in ACAD8. To date, 10 of the 13 isobutyryl-CoA dehydrogenase–deficient patients remain asymptomatic, two were lost to follow-up, and one patient required frequent hospitalizations due to emesis and dehydration but is developing normally at 5 years of age. ConclusionAlthough the natural history of isobutyryl-CoA dehydrogenase deficiency must be further defined, we have developed an algorithm for rapid laboratory evaluation of neonates with an isolated elevation of C4-acylcarnitine identified through newborn screening.

Identification of novel mutations of the HADHA and HADHB genes in patients with mitochondrial trifunctional protein deficiency

Patients with long-chain 3-hydroxyacyl coenzyme A dehydrogenase (LCHAD) deficiency manifest hypoketotic hypoglycemia, hepatomegaly, hypotonia, lactic acidemia, acute renal failure, cardiomyopathy, and sudden death. We describe four novel mutations of the alpha- and beta-subunits of the mitochondrial trifunctional protein in four patients from three unrelated families. Their plasma acylcarnitine profiles suggested the presence of LCHAD deficiency by demonstrating highly elevated 3-hydroxyacyl carnitines by tandem mass spectrometry (MS/MS). Patients 1 and 2 had siblings who had died of lactic acidemia during the neonatal period. These patients also manifested lactic acidemia and died in the neonatal period. Patient 3 had a family history of Reye-like syndrome. She exhibited acute renal failure, rhabdomyolysis, pericardial effusion, and myopathy at the age of 12 years. DNA analysis of patients 1 and 2 revealed homozygosity for a c.1689+2T>G mutation of the HADHA gene, resulting in the skipping of exon 16 with an in-frame 69-bp deletion. Patient 3 was a compound heterozygosity of the HADHB gene, N307D/N389D. Patient 4, a 25-month-old baby, manifested recurrent episodes of lethargy, metabolic acidosis, elevated liver enzymes, and dark urine from the age of 10 months. Mutation analysis of the HADHB gene of patient 4 identified compound heterozygosity of N114D/N307D.

Effects of higher dietary protein intake on energy balance and metabolic control in children with long-chain 3-hydroxy acyl-CoA dehydrogenase (LCHAD) or trifunctional protein (TFP) deficiency

The incidence of overweight and obesity is increasing among children with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) or mitochondrial trifunctional (TFP) deficiency. Traditional treatment includes fasting avoidance and consumption of a low-fat, high-carbohydrate diet. A diet higher in protein and lower in carbohydrate may help to lower total energy intake while maintaining good metabolic control. To determine the short-term safety and efficacy of a high protein diet, subjects were admitted to the General Clinical Research Center and fed an ad-libitum high-protein diet and a high-carbohydrate diet for 6 days each using a randomized, crossover design. Nine subjects with LCHAD or TFP deficiency, age 7–14 were enrolled. Body composition was determined by DEXA. Total energy intake was evaluated daily. Resting energy expenditure and substrate utilization were determined by indirect calorimetry. Post-prandial metabolic responses of plasma glucose, insulin, leptin, ghrelin, acylcarnitines, and triglyceride were determined in response to a liquid meal. Subjects had a higher fat mass, lower lean mass and higher plasma leptin levels compared to reference values. While on the high protein diet energy consumption was an average of 50 kcals/day lower ( p = 0.02) and resting energy expenditure was an average of 170 kcals/day higher ( p = 0.05) compared to the high carbohydrate diet. Short-term higher protein diets were safe, well tolerated, and resulted in lowered energy intake and increased energy expenditure than the standard high-carbohydrate diet. Long-term studies are needed to determine whether higher protein diets will reduce the risk of overweight and obesity in children with LCHAD or TFP deficiency.

Biochemical findings in common inborn errors of metabolism

The application of tandem mass spectrometry (MS/MS) to newborn screening has led to the detection of patients with a wider spectrum of inborn errors of metabolism. A definitive diagnosis can often be established early enough to start treatment before symptoms appear. Here, we review common biochemical findings in disorders caused by deficiency of 3-methylcrotonyl-CoA carboxylase, isobutyryl-CoA dehydrogenase, 2-methyl-3-hydroxybutyryl-CoA dehydrogenase, 3-ketothiolase, 2-methylbutyryl-CoA dehydrogenase, and medium chain acyl CoA dehydrogenase. The diagnosis of these disorders requires biochemical confirmation by measurement of plasma acylcarnitine profile, urine organic acids, and urine acylglycine profiles followed by measurement of enzyme activity or detection of causative mutations. Early treatment can improve the outcome of these disorders.

Refining the diagnosis of mitochondrial HMG‐CoA synthase deficiency

Mitochondrial HMG-CoA synthase deficiency is an inherited metabolic disorder caused by a defect in the enzyme that regulates the formation of ketone bodies. Patients present with hypoketotic hypoglycaemia, encephalopathy and hepatomegaly, usually precipitated by an intercurrent infection or prolonged fasting. The diagnosis may easily be missed as previously reported results of routine metabolic investigations, urinary organic acids and plasma acylcarnitines may be nonspecific or normal, and a high index of suspicion is required to proceed to further confirmatory tests. We describe a further acute case in which the combination of urinary organic acids, low free carnitine and changes in the plasma acylcarnitine profile on carnitine supplementation were very suggestive of a defect in ketone synthesis. The diagnosis of mitochondrial HMG-CoA synthase deficiency was confirmed on genotyping, revealing two novel mutations: c.614G > A (R188H) and c.971T > C (M307T). A further sibling, in whom the diagnosis had not been made acutely, was also found to be affected. The possible effects of these mutations on enzyme activity are discussed.

Metabolic effects of intravenous LCT or MCT/LCT lipid emulsions in preterm infants

Most lipid emulsions for parenteral feeding of premature infants are based on long-chain triacylglycerols (LCTs), but inclusion of medium-chain triacylglycerols (MCTs) might provide a more readily oxidizable energy source. The influence of these emulsions on fatty acid composition and metabolism was studied in 12 premature neonates, who were randomly assigned to an LCT emulsion (control) or an emulsion with a mixture of MCT and LCT (1:1). On study day 7, all infants received [13C]linoleic (LA) and [13C]alpha-linolenic acid (ALA) tracers orally. Plasma phospholipid (PL) and triacylglycerol (TG) fatty acid composition and 13C enrichments of plasma PL fatty acids were determined on day 8. After 8 days of lipid infusion, plasma TGs in the MCT/LCT group had higher contents of C8:0 (0.50 +/- 0.60% vs. 0.10 +/- 0.12%; means +/- SD) and C10:0 (0.66 +/- 0.51% vs. 0.15 +/- 0.17%) than controls. LA content of plasma PLs was slightly lower in the MCT/LCT group (16.47 +/- 1.16% vs. 18.57 +/- 2.09%), whereas long-chain polyunsaturated derivatives (LC-PUFAs) of LA and ALA tended to be higher. The tracer distributions between precursors and products (LC-PUFAs) were not significantly different between groups. Both lipid emulsions achieve similar plasma essential fatty acid (EFA) contents and similar proportional conversion of EFAs to LC-PUFAs. The MCT/LCT emulsion seems to protect EFAs and LC-PUFAs from beta-oxidation.

Bile acylcarnitine profiles in pediatric liver disease do not interfere with the diagnosis of long-chain fatty acid oxidation defects

Background Plasma acylcarnitine measurement is an important diagnostic tool for inherited disorders of fatty acid and organic acid metabolism. Biliary excretion has been shown to be the primary route of excretion for acylcarnitines and analysis of bile acylcarnitine profiles may provide greater sensitivity for detecting metabolic disorders. Disorders of fatty acid oxidation frequently present with deranged liver function and the effect of hepatic disease on biliary acylcarnitine excretion are unknown. Methods We measured biliary acylcarnitine levels in pediatric patients aged 6 months to 1 year undergoing open liver biopsy with prospectively determined non-metabolic liver disease in order to determine the effect of the liver disease on acylcarnitine excretion. Bile was collected in syringes and was transported immediately and stored at − 70 °C until the time of testing. The disease patient population consisted of 2 patients with known defects in long- and short-chain fatty acid oxidation (long-chain L-3-hydroxy acyl-CoA dehydrogenase: LCHAD and short-chain L-3-hydroxy acyl-CoA dehydrogenase: SCHAD). The sample from the LCHAD patient was collected at autopsy and the patient with SCHAD deficiency was subsequently diagnosed as part of the prospective study and removed from the unknown etiology group. Acylcarnitine profiles were obtained for each specimen as butylated derivatives using tandem mass spectrometry. Results The non-metabolic liver disease had no effect on the diagnostic value of bile acylcarnitine levels for detecting LCHAD deficiency. The concentrations of bile long-chain acylcarnitine species analyzed from patients with non-metabolic liver disease were far lower than the levels seen in LCHAD deficiency which also demonstrated a characteristic pattern of 3-hydroxyacylcarnitine excretion. In SCHAD deficiency, for which pathognomonic markers have not yet been established, bile analysis did not improve the diagnostic ability. Conclusion The analysis of bile acylcarnitines for the diagnosis of long-chain fatty acid oxidation defects will provide unbiased information even in the presence of severe non-metabolic liver disease.