Carnitine palmitoyltransferase II deficiency: successful anaplerotic diet therapy

BACKGROUND

Carnitine palmitoyltransferase II (CPT II) deficiency is an important cause of recurrent rhabdomyolysis in children and adults. Current treatment includes dietary fat restriction, with increased carbohydrate intake and exercise restriction to avoid muscle pain and rhabdomyolysis.

METHODS

CPT II enzyme assay, DNA mutation analysis, quantitative analysis of acylcarnitines in blood and cultured fibroblasts, urinary organic acids, the standardized 36-item Short-Form Health Status survey (SF-36) version 2, and bioelectric impedance for body fat composition. Diet treatment with triheptanoin at 30% to 35% of total daily caloric intake was used for all patients.

RESULTS

Seven patients with CPT II deficiency were studied from 7 to 61 months on the triheptanoin (anaplerotic) diet. Five had previous episodes of rhabdomyolysis requiring hospitalizations and muscle pain on exertion prior to the diet (two younger patients had not had rhabdomyolysis). While on the diet, only two patients experienced mild muscle pain with exercise. During short periods of noncompliance, two patients experienced rhabdomyolysis with exercise. None experienced rhabdomyolysis or hospitalizations while on the diet. All patients returned to normal physical activities including strenuous sports. Exercise restriction was eliminated. Previously abnormal SF-36 physical composite scores returned to normal levels that persisted for the duration of the therapy in all five symptomatic patients.

CONCLUSIONS

The triheptanoin diet seems to be an effective therapy for adult-onset carnitine palmitoyltransferase II deficiency.

Differentiation of long-chain fatty acid oxidation disorders using alternative precursors and acylcarnitine profiling in fibroblasts

The differentiation of carnitine-acylcarnitine translocase deficiency (CACT) from carnitine palmitoyltransferase type II deficiency (CPT-II) and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency from mitochondrial trifunctional protein deficiency (MTP) continues to be ambiguous using current acylcarnitine profiling techniques either from plasma or blood spots, or in the intact cell system (fibroblasts/amniocytes). Currently, enzyme assays are required to unequivocally differentiate CACT from CPT-II, and LCHAD from MTP. Over the years we have studied the responses of numerous FOD deficient cell lines to both even and odd numbered fatty acids of various chain lengths as well as branched-chain amino acids. In doing so, we discovered diagnostic elevations of unlabeled butyrylcarnitine detected only in CACT deficient cell lines when incubated with a shorter chain fatty acid, [7-2H3]heptanoate plus l-carnitine compared to the routinely used long-chain fatty acid, [16-2H3]palmitate. In monitoring the unlabeled C4/C5 acylcarnitine ratio, further differentiation from ETF/ETF-DH is also achieved. Similarly, incubating LCHAD and MTP deficient cell lines with the long-chain branched fatty acid, pristanic acid, and monitoring the C11/C9 acylcarnitine ratio has allowed differentiation between these disorders. These methods may be considered useful alternatives to specific enzyme assays for differentiation between these long-chain fatty acid oxidation disorders, as well as provide insight into new treatment strategies.

Respiratory complex II defect in siblings associated with a symptomatic secondary block in fatty acid oxidation

The mitochondrial oxidative phosphorylation and fatty acid oxidation pathways have traditionally been considered independent major sources of cellular energy production; however, case reports of patients with specific enzymatic defects in either pathway have suggested the potential for a complex interference between the two. This study documents a new site of interference between the two pathways, a site in respiratory complex II capable of producing clinical signs of a block in fatty acid oxidation and reduced in vitro activity of acyl-CoA dehydrogenases. The initial patient, and later her newborn sibling, had mildly dysmorphic features, lactic acidosis and a defect in mitochondrial respiratory complex II associated with many biochemical features of a block in fatty acid oxidation. Results of in vitro probing of intact fibroblasts from both patients with methyl[2H3]palmitate and L-carnitine revealed greatly increased [2H3]butyrylcarnitine; however, the ratio of dehydrogenase activity with butyryl-CoA with anti-MCAD inactivating antibody (used to reveal SCAD-specific activity) to that with octanoyl-CoA was normal, excluding a selective SCAD or MCAD deficiency. Respiratory complex II was defective in both patients, with an absent thenoyltrifluoroacetone-sensitive succinate Q reductase activity that was partially restored by supplementation with duroquinone. Although secondary, the block in fatty acid oxidation was a major management problem since attempts to provide essential fatty acids precipitated acidotic decompensations. This study reinforces the need to pursue broadly the primary genetic defect within these two pathways, making full use of increasingly available functional and molecular diagnostic tools.

Prenatal diagnosis of multiple acyl-CoA dehydrogenase deficiency: association with elevated alpha-fetoprotein and cystic renal changes

We report the occurrence of multiple acyl-CoA dehydrogenase deficiency (MADD) in two consecutive pregnancies in a young, Caucasian, non-consanguineous couple. In the first pregnancy, the maternal serum alpha-fetoprotein was elevated. A sonogram showed growth delay, cystic renal disease, and oligohydramnios; the parents decided to terminate the pregnancy. Postmortem examination confirmed the cystic renal disease and showed hepatic steatosis, raising the suspicion of a metabolic disorder. The diagnosis of MADD was made by immunoblot studies on cultured fibroblasts. In the subsequent pregnancy, a sonogram at 15 weeks' gestation showed an early growth delay but normal kidneys. The maternal serum and amniotic fluid concentrations of alpha-fetoprotein were elevated, and the amniotic fluid acylcarnitine profile was consistent with MADD. In vitro metabolic studies on cultured amniocytes confirmed the diagnosis. A follow-up sonogram showed cystic renal changes. These cases provide additional information regarding the evolution of renal changes in affected fetuses and show a relationship with elevated alpha-fetoprotein, which may be useful in counseling the couple at risk. MADD should be considered in the differential diagnosis of elevated alpha-fetoprotein and cystic renal disease. Early growth delay may be an additional feature.

Oxidation of unsaturated fatty acids by human fibroblasts with very-long-chain acyl-CoA dehydrogenase deficiency: aspects of substrate specificity and correlation with clinical phenotype

The degradation of unsaturated fatty acids was examined in fibroblasts from 16 patients with very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. Analysis of acylcarnitine intermediates following incubation of intact human cells with these compounds revealed that the milder clinical phenotypes could be distinguished from the severe cardiomyopathic phenotype. These findings may reflect more effective contributions of alternate pathways in the milder forms of the disease. Incubation of VLCAD-deficient cells with cis-9 or trans-9 unsaturated fatty acids indicate that VLCAD is largely responsible for the 2,3-dehydrogenation of cis-5 or trans-5 intermediates in fibroblasts. The first two cycles of beta-oxidation with oleic and linoleic acids occur in the absence of VLCAD activity suggesting the presence of an additional acyl-CoA dehydrogenase or alternate pathway for the oxidation of these unsaturated fatty acids. These observations have clinical relevance for determining diagnosis, prognosis and strategies for dietary treatment of these patients.

Carnitine/acylcarnitine translocase deficiency (neonatal phenotype): successful prenatal and postmortem diagnosis associated with a novel mutation in a single family

The neonatal phenotype of carnitine-acylcarnitine translocase (CACT) deficiency is one of the most severe and usually lethal mitochondrial fat oxidation disorders characterized by hypoketotic hypoglycemia, hyperammonemia, cardiac abnormalities, and early death. In this study, the proband was the daughter of consanguineous Hispanic parents. At 36 h of life, she had bradycardia and died at 4 days of age without a specific diagnosis. In a subsequent pregnancy, prenatal counseling and amniocentesis were provided. Incubation of the amniocytes from this pregnancy and fibroblasts (from the dead proband) with [16-(2)H(3)]palmitic acid and analysis by tandem mass spectrometry revealed an increasedconcentration of [16-(2)H(3)]palmitoylcarnitine, suggesting the diagnoses of either CACT or carnitine palmitoyltransferase II (CPT-II) deficiency. CACT enzyme activity was absent in both cell lines. Molecular investigation of cDNA from the dead proband and her affected sibling revealed aberrant CACT cDNA species, including exon 3 skipping, both exon 3 and 4 skipping, and a 13-bp insertion at cDNA position 388. Investigation of these cell lines for mutations affecting CACT RNA processing by analysis of CACT gene sequences, including intron and exon boundaries, revealed a single nucleotide G deletion at the donor site in intron 3 which resulted in exon skipping and a 13-bp insertion. The proband and her affected sibling were homozygous for this deletion.

2-Methylbutyryl-coenzyme A dehydrogenase deficiency: a new inborn error of L-isoleucine metabolism

An 4-mo-old male was found to have an isolated increase in 2-methylbutyrylglycine (2-MBG) and 2-methylbutyrylcamitine (2-MBC) in physiologic fluids. In vitro oxidation studies in cultured fibroblasts using 13C- and 14C-labeled branched chain amino acids indicated an isolated block in 2-methylbutyryl-CoA dehydrogenase (2-MBCDase). Western blotting revealed absence of 2-MBCDase protein in fibroblast extracts; DNA sequencing identified a single 778 C>T substitution in the 2-MBCDase coding region (778 C>T), substituting phenylalanine for leucine at amino acid 222 (L222F) and absence of enzyme activity for the 2-MBCDase protein expressed in Escherichia coli. Prenatal diagnosis in a subsequent pregnancy suggested an affected female fetus, supporting an autosomal recessive mode of inheritance. These data confirm the first documented case of isolated 2-MBCDase deficiency in humans.

Evidence for a short-chain carnitine-acylcarnitine translocase in mitochondria specifically related to the metabolism of branched-chain amino acids

Carnitine-acylcarnitine translocase (CATR) deficiency is a severe defect in fatty acid oxidation which presents early in life most frequently with hypoglycemia, hyperammonemia, and severe cardiac abnormalities. CATR exchanges acylcarnitines of various chain lengths for free carnitine across the mitochondrial membrane. In vitro studies in intact fibroblasts from patients with documented deficiency of CATR were probed with stable-isotope-labeled precursors and the resulting acylcarnitines were analyzed by tandem mass spectrometry. After a 72-h incubation with l-[(2)H(3)]carnitine the translocase-deficient cells produced acylcarnitines in which the deuterium was incorporated into short-chain acylcarnitines, C2-C5. Experiments with simultaneous incubation of l-[(2)H(3)]carnitine and l-[(13)C(6)]isoleucine produced [(13)C(5)]2-methylbutyryl-[(2)H(3)]carnitine and [(13)C(3)]propionyl-[(2)H(3)]carnitine indicating exchange of labeled acylcarnitine from inside the mitochondrial matrix with labeled free carnitine. These studies support the possible existence of a "branched-chain" carnitine-acylcarnitine translocator in mitochondria.

Identification of two novel mutations in the hypoglycemic phenotype of very long chain acyl-CoA dehydrogenase deficiency

Very long chain acyl-CoA dehydrogenase (VLCAD) catalyzes the initial step of long chain fatty acid oxidation in the mitochondria. Patients with VLCAD deficiency have recently been observed with two clinical phenotypes. The cardiac form presents with an early onset cardiomyopathy and a high incidence of infant death, while the hypoglycemic form resembles medium chain acyl-CoA dehydrogenase (MCAD) manifesting with hypoketotic hypoglycemia. In our investigation on the molecular basis for these phenotypes, we identified two novel mutations in one VLCAD patient with the hypoglycemic form, a C953T (Pro318Leu) mutation in exon 10 resulting in a substitution of proline 318 by leucine on one allele, and a C1194A (Tyr398Stop) mutation in exon 12 which created a premature stop codon TAA on another allele. The Tyr398Stop mutation may result in a truncated protein or instable messenger RNA.

Recent developments in the investigation of inherited metabolic disorders using cultured human cells

Thepurpose of this paper is to share experience with our systems and review recent "in vitro" methods using intact cells (fibroblasts, amniocytes) in which entire metabolic pathways can be probed for inherited metabolic defects reflected by elevations of intermediates determined by tandem mass spectrometry, HPLC, or gas chromatography-mass spectrometry. Currently, one can explore the integrity of mitochondrial fat oxidation, peroxisomal degradation of methyl-branched fatty acids (e.g., pristanate), and the mitochondrial degradation of the branched chain amino acids (leucine, valine, and isoleucine). For many of the diseases, the specific defect can be recognized from the acylcarnitine profile resulting from incubation of the intact cells with stable-isotope-labeled precursors to the particular pathway. This approach has also been successful in identifying new inherited metabolic disorders, biochemical correlation with clinical phenotypes of individual defects, and sequential oxidation of fatty acids by peroxisomal-mitochondrial interaction.

Isolated isobutyryl-CoA dehydrogenase deficiency: an unrecognized defect in human valine metabolism

A 2-year-old female was well until 12 months of age when she was found to be anemic and had dilated cardiomyopathy. Total plasma carnitine was 6 microM and acylcarnitine analysis while receiving carnitine supplement revealed an increase in the four-carbon species. Urine organic acids were normal. In vitro analysis of the mitochondrial pathways for beta oxidation, and leucine, valine, and isoleucine metabolism was performed in fibroblasts using stable isotope-labeled precursors to these pathways followed by acylcarnitine analysis by tandem mass spectrometry. 16-2H3-palmitate was metabolized normally down to the level of butyryl-CoA thus excluding SCAD deficiency. 13C6-leucine and 13C6-isoleucine were also metabolized normally. 13C5-valine incubation revealed a significant increase in 13C4-isobutyrylcarnitine without any incorporation into propionylcarnitine as is observed normally. These same precursors were also evaluated in fibroblasts with proven ETF-QO deficiency in which acyl-CoA dehydrogenase deficiencies in each of these pathways was clearly identified. These results indicate that in the human, there is an isobutyryl-CoA dehydrogenase which exists as a separate enzyme serving only the valine pathway in addition to the 2-methyl branched-chain dehydrogenase which serves both the valine and the isoleucine pathways in both rat and human.

Methylmalonic semialdehyde dehydrogenase deficiency: psychomotor delay and methylmalonic aciduria without metabolic decompensation

A patient presenting with developmental delay but no episodes of metabolic acidosis was found to excrete significant amounts of methylmalonate (MMA) without any associated increased excretion of malonate, ethylmalonate, 3-hydroxypropionate, or beta-alanine. In contrast to patients with methylmalonic aciduria due to deficient mutase or impaired cobalamin metabolism, there was no increase of propionylcarnitine in blood or urine. The activity of methylmalonyl-CoA mutase and the pathway for cobalamin metabolism were also intact. The quantitative levels of the various labeled enantiomers of 3-hydroxyisobutyric (3-HIBA), 3-aminoisobutyric (3-AIBA), MMA, and propionylcarnitine were compared following separate intravenous infusions of equimolar doses of [2H8]-valine or [2H4]thymine in this patient and another with methylmalonyl-CoA mutase deficiency. Levels of labeled S- and R-3-HIBA and S- and R-3-AIBA indicated an isolated defect in methylmalonic semialdehyde dehydrogenase in this patient. This condition can be recognized by plasma MMA levels of approximately 8.5 microM (cf. 400 microM in mutase deficiency), urine MMA of 20-55 micromol/kg/24 h (cf. 1150 micromol/kg/24 h), no increase in propionylcarnitine following an oral carnitine load, and increased excretion of S-3-AIBA-nearly 10 times that observed in mutase deficiency. The ratio of R-AIBA to S-AIBA of <1 also reflects this disorder.

Phytanic acid and pristanic acid are oxidized by sequential peroxisomal and mitochondrial reactions in cultured fibroblasts

The relationship between peroxisomal and mitochondrial oxidation of the methyl branched fatty acids, phytanic acid and pristanic acid, was studied in normal and mutant human skin fibroblasts with established enzyme deficiencies. Tandem mass spectrometry was used for analysis of the acylcarnitine intermediates. In normal cells, 4,8-dimethylnonanoylcarnitine (C11:0) and 2,6-dimethylheptanoylcarnitine (C9:0) accumulated after incubation with either phytanic acid or pristanic acid. These intermediates were not observed when peroxisome-deficient cells from Zellweger patients were incubated with the same compounds, pointing to the involvement of peroxisomes in the formation of these acylcarnitine intermediates. Similar experiments with fibroblasts deficient in carnitine palmitoyltransferase I, carnitine-acylcarnitine translocase or carnitine palmitoyltransferase II revealed that mitochondrial carnitine palmitoyltransferase I is not required for the oxidation of phytanic acid or pristanic acid, whereas both carnitine-acylcarnitine translocase and carnitine palmitoyltransferase II are necessary. These studies demonstrate that both phytanic acid and pristanic acid are initially oxidized in peroxisomes to 4,8-dimethylnonanoyl-CoA, which is converted to the corresponding acylcarnitine (presumably by peroxisomal carnitine octanoyltransferase), and exported to the mitochondrion. After transport across the mitochondrial membrane and transfer of the acylgroup to coenzyme A, further oxidation to 2,6-dimethylheptanoyl-CoA occurs.

Methylmalonic aciduria in pregnancy: a case report

Methylmalonic aciduria is a rare metabolic disorder of amino acid metabolism that is characterized by accumulation of large amounts of methylmalonic acid in the blood and urine. To our knowledge this is the first case report of a patient with methylmalonic aciduria who carried a pregnancy to term; the outcome was favorable despite high levels of methylmalonic acid in the serum and urine.

Intravenous L-carnitine and acetyl-L-carnitine in medium-chain acyl-coenzyme A dehydrogenase deficiency and isovaleric acidemia

The purpose of this study was to determine whether treatment with L-carnitine or acetyl-L-carnitine enhances the turnover of lipid or branched-chain amino acid oxidation in patients with inborn errors of metabolism. Increasing i.v. doses of L-carnitine and acetyl-L-carnitine were given to one patient with medium-chain acyl-CoA dehydrogenase deficiency and to another with isovaleric acidemia. Both patients were in stable condition and receiving oral L-carnitine supplements. The excretion of carnitine and disease-specific metabolites was measured. The incorporation of L-carnitine in the intracellular pool was demonstrated using stable isotopes and mass spectrometry. Increasing doses of either i.v. L-carnitine or acetyl-L-carnitine did not stimulate the excretion of octanoylcarnitine in the patient with medium-chain acyl-CoA dehydrogenase deficiency, nor did it raise the plasma levels of either cis-4-decenoate or octanoylcarnitine. Similarly, increasing doses of either i.v. L-carnitine or acetyl-L-carnitine did not enhance the excretion of isovalerylcarnitine in a patient with isovaleric acidemia. The excretion of isovalerylglycine actually decreased. We conclude that there was no evidence of enhanced fatty acid beta-oxidation or enhanced branched-chain amino acid oxidation in vivo by the administration of high doses of L-carnitine or acetyl-L-carnitine in these two patients. Because only one individual with each disorder was studied, the data are only indicative and may not necessarily be representative of all individuals with these disorders. Definite settlement of this issue will require further studies in additional subjects.

Automated Analysis for Free and Short-Chain Acylcarnitine in Plasma with a Centrifugal Analyzer

We describe a fully automated, spectrophotometric assay of free and total carnitine in plasma ultrafiltrates. The method, suitable for routine application in most hospital laboratories, incorporates the hydrolysis of acylcarnitines to free carnitine within the program of a Cobas Fara II centrifugal analyzer. The hydrolysis is monitored and calibrated with standard solutions containing octanoylcarnitine. Results correlated well with those from a reference isotope-dilution mass spectrometric assay. The ability to analyze a batch of samples for both free and total carnitine within 90 min enables analysis of &gt; or = 100 samples per day. Used in conjunction with acylcarnitine species identification by mass spectrometry, the Cobas assay facilitates the diagnosis of carnitine-deficiency syndromes and specific metabolic disorders.

Automated analysis for free and short-chain acylcarnitine in plasma with a centrifugal analyzer

We describe a fully automated, spectrophotometric assay of free and total carnitine in plasma ultrafiltrates. The method, suitable for routine application in most hospital laboratories, incorporates the hydrolysis of acylcarnitines to free carnitine within the program of a Cobas Fara II centrifugal analyzer. The hydrolysis is monitored and calibrated with standard solutions containing octanoylcarnitine. Results correlated well with those from a reference isotope-dilution mass spectrometric assay. The ability to analyze a batch of samples for both free and total carnitine within 90 min enables analysis of > or = 100 samples per day. Used in conjunction with acylcarnitine species identification by mass spectrometry, the Cobas assay facilitates the diagnosis of carnitine-deficiency syndromes and specific metabolic disorders.

Isolation and biochemical characterization of intertypic recombinants of foot-and-mouth disease virus

Recombinants were isolated between two European serotypes (O and A) and between two of the most distantly related serotypes (O from Europe and SAT2 from Africa) using appropriate ts mutants in an infectious centre assay. The recombinants were characterised by electrofocusing of their induced proteins and by RNase-T1 fingerprinting of their RNA. The approximate location of the cross-over event in each recombinant was determined by sequencing the unique distinguishable O or A oligonucleotides and locating them within the known genome sequence. Nine different types of recombinant were identified from the two types of cross (O X A and O X SAT) and all had a single cross-over in the middle or 3' half of the genome, i.e. in the nonstructural coding region. Recombination between the most distantly related viruses (O X SAT2) appeared to occur at a lower frequency than recombination between serotypes of the same group (O X A). A higher incidence of recombinant proteins with unique pI was also observed in the O X SAT2 crosses.