Hypoglycin A concentrations in seeds of Acer pseudoplatanus trees growing on atypical myopathy-affected and control pastures

Background

Hypoglycin A, found in seeds of Acer negundo, appears to cause seasonal pasture myopathy (SPM) in North America and is implicated in atypical myopathy (AM) in Europe. Acer negundo is uncommon in Europe. Thus, the potential source of hypoglycin A in Europe is unknown.

Hypothesis and Objectives

We hypothesized that seeds of Acer pseudoplatanus were the source of hypoglycin A in Europe. Our objective was to determine the concentration of hypoglycin A in seeds of A. pseudoplatanus trees located in pastures where previous cases of AM had occurred.

Animals

None.

Methods

University of Berne records were searched to retrospectively identify 6 farms with 10 AM cases and 11 suspected AM deaths between 2007 and 2011. During October 2012, A. pseudoplatanus seeds were collected from 2 to 6 trees per pasture on 6 AM farms (7 pastures) from trees in or close to 2 pastures on 2 control farms where AM had not been previously reported. Hypoglycin A in seeds was analyzed by GC–MS.

Results

Acer pseudoplatanus trees were identified on all AM pastures. Hypoglycin A was detected in all A. pseudoplatanus seeds in highly variable concentrations ranging from 0.04 to 2.81 μg/mg (mean 0.69) on AM farms and 0.10 to 9.12 μg/mg (mean 1.59) on control farms.

Conclusion and Clinical Importance

Preventing horses from grazing pastures containing A. pseudoplatanus seeds during late fall and early spring might be the best means to prevent AM.

Identification of methylenecyclopropyl acetic acid in serum of European horses with atypical myopathy

REASONS FOR PERFORMING STUDY

It is hypothesised that European atypical myopathy (AM) has a similar basis as seasonal pasture myopathy in North America, which is now known to be caused by ingestion of hypoglycin A contained in seeds from the tree Acer negundo. Serum from horses with seasonal pasture myopathy contained the conjugated toxic metabolite of hypoglycin A, methylenecyclopropyl acetic acid (MCPA).

STUDY DESIGN

Retrospective study on archived samples.

OBJECTIVES

1) To determine whether MCPA-carnitine was present in serum of European horses confirmed to have AM; 2) to determine whether Acer negundo or related Acer species were present on AM pastures in Europe.

METHODS

Concentrations of MCPA-carnitine were analysed in banked serum samples of 17 AM horses from Europe and 3 diseased controls (tetanus, neoplasia and exertional rhabdomyolysis) using tandem mass spectrometry. Atypical myopathy was diagnosed by characteristic serum acylcarnitine profiles. Pastures of 12 AM farms were visited by experienced botanists and plant species were documented.

RESULTS

Methylenecyclopropyl acetic acid-carnitine at high concentrations (20.39 ± 17.24 nmol/l; range 0.95-57.63 nmol/l; reference: <0.01 nmol/l) was identified in serum of AM but not disease controls (0.00 ± 0.00 nmol/l). Acer pseudoplatanus but not Acer negundo was present on all AM farms.

CONCLUSIONS

Atypical myopathy in Europe, like seasonal pasture myopathy in North America, is highly associated with the toxic metabolite of hypoglycin A, MCPA-carnitine. This finding coupled with the presence of a tree of which seeds are known to also contain hypoglycin A indicates that ingestion of Acer pseudoplatanus is the probable cause of AM. This finding has major implications for the prevention of AM.

Seasonal pasture myopathy/atypical myopathy in North America associated with ingestion of hypoglycin A within seeds of the box elder tree

REASONS FOR PERFORMING STUDY

We hypothesised that seasonal pasture myopathy (SPM), which closely resembles atypical myopathy (AM), was caused by ingestion of a seed-bearing plant abundant in autumn pastures.

OBJECTIVES

To identify a common seed-bearing plant among autumn pastures of horses with SPM, and to determine whether the toxic amino acid hypoglycin A was present in the seeds and whether hypoglycin metabolites were present in SPM horse serum or urine.

METHODS

Twelve SPM cases, 11 SPM pastures and 23 control farms were visited to identify a plant common to all SPM farms in autumn. A common seed was analysed for amino acid composition (n = 7/7) by GC-MS and its toxic metabolite (n = 4/4) identified in conjugated form in serum [tandem mass spectrometry (MS/MS)] and urine [gas chromatography (GC) MS]. Serum acylcarnitines and urine organic acid profiles (n = 7) were determined for SPM horses.

RESULTS

Seeds from box elder trees (Acer negundo) were present on all SPM and 61% of control pastures. Hypoglycin A, known to cause acquired multiple acyl-CoA dehydrogenase deficiency (MADD), was found in box elder seeds. Serum acylcarnitines and urine organic acid profiles in SPM horses were typical for MADD. The hypoglycin A metabolite methylenecyclopropylacetic acid (MCPA), known to be toxic in other species, was found in conjugated form in SPM horse serum and urine. Horses with SPM had longer turn-out, more overgrazed pastures, and less supplemental feeding than control horses.

POTENTIAL RELEVANCE

For the first time, SPM has been linked to a toxin in seeds abundant on autumn pastures whose identified metabolite, MCPA, is known to cause acquired MADD, the pathological mechanism behind SPM and AM. Further research is required to determine the lethal dose of hypoglycin A in horses, as well as factors that affect annual seed burden and hypoglycin A content in Acer species in North America and Europe.

Guanidinoacetate methyltransferase deficiency: first steps to newborn screening for a treatable neurometabolic disease

BACKGROUND

GAMT deficiency is an autosomal recessive disorder of creatine biosynthesis resulting in severe neurological complications in untreated patients. Currently available treatment is only successful to stop disease progression, but is not sufficient to reverse neurological complications occurring prior to diagnosis. Normal neurodevelopmental outcome in a patient, treated in the newborn period, highlights the importance of early diagnosis.

METHODS

Targeted mutation analysis (c.59G>C and c.327G>A) in the GAMT gene by the QIAxcel system and GAA measurement by a novel two-tier method were performed in 3000 anonymized newborn blood dot spot cards.

RESULTS

None of the targeted mutations were detected in any newborn. Two novel heterozygous variants (c.283_285dupGTC; p.Val95dup and c.278_283delinsCTCGATGCAC; p.Asp93AlafsX35) were identified by coincidence. Carrier frequency for these insertion/deletion types of GAMT mutations was 1/1475 in this small cohort of newborns. GAA levels were at or above the 99th percentile (3.12 μmol/l) in 4 newborns. Second-tier testing showed normal results for 4 newborns revealing 0.1% false positive rate. No GAMT mutations were identified in 4 of the newborns with elevated GAA levels in the first tier testing.

CONCLUSION

This is the first two-tier study to investigate carrier frequency of GAMT deficiency in the small cohort of newborn population to establish evidence base for the first steps toward newborn screening for this treatable neurometabolic disorder.

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.

Determination of plaque inhibitory activity of adenine arabinoside (9-beta-D-arabinofuranosyladenine) for herpesviruses using an adenosine deaminase inhibitor

The in vitro susceptibility of type 1 and type 2 strains of Herpesvirus hominis to 9-beta-d-arabinofuranosyladenine (adenine arabinoside, ara-A) was measured in a system where deamination was inhibited. Under these conditions, it was possible to measure the activity of low concentrations of ara-A. It was determined that plaque inhibitory concentration for type 1 viruses was less than 3 mug/ml for all strains tested. The plaque inhibitory concentration for 7 of 10 type 2 strains was also less than 3 mug/ml. The method used identified and controlled the interaction between antiviral agent (ara-A) and the indicator system, human skin fibroblastic cells. Otherwise, metabolism of ara-A resulted in rapid enzymatic degradation and loss of antiviral activity.

Effect of adenosine deaminase upon the antiviral activity in vitro of adenine arabinoside for vaccinia virus

This study determined that the effect of 9-beta-d-arabinofuranosyl-adenine (adenine arabinoside, Ara-A) upon vaccinia virus plaque development in the stable monkey kidney line, LLC-MK(2), was increased approximately 40-fold when an inhibitor of adenosine deaminase (ADA) was added to the tissue culture media along with infective inocula. The concentration of Ara-A required to completely suppress plaque development (total plaque inhibitory concentration(100); TPIC(100)) was greater than 10 mug/ml. However, when ADA activity was inhibited, the TPIC(100) was 0.5 mug/ml or less. Chromatographic assay of arabinosylpurines in the media provided evidence that adenine arabinoside was rapidly deaminated to 9-beta-d-arabinofuranosylhypoxanthine by the cellular monolayers, in the absence of animal serum, and that the rate of deamination, at 5 mug/ml, by the cells was equal to the rate of diffusion of Ara-A across the cellular membrane. The half-life of Ara-A in the media, starting with 5 mug/ml, was 2 to 3 h and shorter at lower concentrations. The study demonstrates the profound effect that an indicator system, acting as an intact biological unit, can have upon a potential antiviral compound.

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.

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.

Death caused by perioperative fasting and sedation in a child with unrecognized very long chain acyl-coenzyme A dehydrogenase deficiency

An adopted 3(1/2)-year-old girl with no prior medical problems died after a routine dental procedure. More than 2 years later, acylcarnitine analysis of dried blood found on her bedding revealed she had very long chain acyl-coenzyme A dehydrogenase (VLCAD) deficiency. Perioperative oral fasting, without intravenous administration of glucose, may be detrimental to children with certain metabolic and endocrine disorders. Newborn screening by tandem mass spectrometry will detect disorders of fatty acid oxidation such as VLCAD and allow early and preventive treatment.

Identification of a novel mutation in patients with medium-chain acyl-CoA dehydrogenase deficiency

A novel mutation was identified in two unrelated patients with medium-chain acyl-CoA dehydrogenase deficiency. First, a 19-year-old Caucasian female presented with a devastating illness, resulting in sudden death in adulthood which is unusual. The second patient, now a 3.5-year-old male, presented at 17 months of age with a hypoglycemic seizure and dehydration. Sequence analysis revealed a novel mutation G617T in exon 8 resulting in an arginine to leucine substitution at codon 206 (R206L). Both patients were compound heterozygous for this G617T and the common mutation A985G.

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.

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.

Deficiency of biotinyl-AMP synthetase activity in fibroblasts of patients with holocarboxylase synthetase deficiency

A simple, rapid assay was developed to diagnose holocarboxylase synthetase deficiency. Holocarboxylase synthetase first catalyzes the formation of biotinyl-AMP from biotin and ATP, an activity designated as biotinyl-AMP synthetase. In the second step of the reaction, biotin is transferred from biotinyl-AMP to the enzymatically inactive apocarboxylase to form an active holocarboxylase. The assay for holocarboxylase synthetase activity therefore requires a protein apocarboxylase substrate which is not readily available. In the assay for biotinyl-AMP synthetase, hydroxylamine reacts nonenzymatically with the product of the enzymatic reaction, biotinyl-AMP, to form biotinylhydroxamate. At the end of the reaction, unreacted radioactive biotin substrate, which is negatively charged at neutral pH, is bound to an anion-exchange resin and a neutral radioactive biotinylhydroxamate product in the supernatant is counted. In fibroblasts from 11 patients with proven holocarboxylase synthetase deficiency, the mean biotinyl-AMP synthetase activity at 25 nM biotin was 4% of the control mean with a range of 0.2 to 8%. This is an improved assay because it does not require preparation of an apocarboxylase substrate and is suitable for the diagnosis of patients with holocarboxylase synthetase deficiency.

Methylmalonic acidemia, cobalamin C type, presenting with cutaneous manifestations

BACKGROUND

Erosive dermatitis resembling the skin lesions of acrodermatitis enteropathica has been described in a number of aminoacidopathies and organic acidemias. In some, the dermatitis is a manifestation of untreated disease, while in others, including methylmalonic acidemia, skin lesions have been ascribed to nutritional deficiency due to therapeutic amino acid restrictions.

OBSERVATIONS

We report 2 cases of methylmalonic acidemia presenting with cutaneous manifestations in the perinatal period before restrictive nutritional interventions. The cutaneous involvement consisted of cheilitis and diffuse erythema with erosions and desquamation. Methylmalonic acidemia, cobalamin C type, was subsequently diagnosed in both cases.

CONCLUSIONS

An erosive, desquamating dermatitis with histopathologic characteristics resembling acrodermatitis enteropathica may be a presenting sign in cobalamin C methylmalonic acidemia, even in the absence of long-standing nutritional restrictions or deficiency.

A new case of malonyl coenzyme A decarboxylase deficiency presenting with cardiomyopathy

A new case of mitochondrial malonyl coenzyme A decarboxylase deficiency is described. The patient presented with an initial episode of metabolic acidosis, seizures, hypoglycemia, and cardiac failure at 2 months of age which slowly resolved. Subsequent evaluations at 4 years of age for developmental delay revealed a prominent elevation of malonic acid in urine. Malonyl carnitine was also elevated. The activity of Malonyl CoA decarboxylase in cultured fibroblasts was 7% of normal.

CONCLUSION

Malonyl CoA decarboxylase deficiency may result in inhibition of fatty acid oxidation, which may account for the cardiomyopathy.

Clustering of mutations in the biotin-binding region of holocarboxylase synthetase in biotin-responsive multiple carboxylase deficiency

Holocarboxylase synthetase (HCS) catalyses the biotinylation of the four biotin-dependent carboxylases found in humans. A deficiency in HCS results in biotin-responsive multiple carboxylase deficiency (MCD). We have identified six different point mutations in the HCS gene in nine patients with MCD. Two of the mutations are frequent among the MCD patients analyzed. Four of the mutations cluster in the putative biotin-binding domain as deduced from the corresponding Escherichia coli enzyme and consistent with an explanation for biotin-responsiveness based on altered affinity for biotin. The two others may define an additional domain involved in biotin-binding or biotin-mediated stabilization of the protein.

D-2-hydroxyglutaric aciduria

Hydroxyglutaric aciduria is detected by gas chromatographic-mass spectrometric analysis, and the D and L forms are quantified by chemical ionization with deuterated internal standards. Patients have recently been described who accumulate the D form, and they appear to be quite different from those with the more common L form. Experience is reported with three patients and an animal model with D-2-hydroxyglutaric aciduria. The phenotype appears to include mental retardation, macrocephaly, hypotonia, seizures, and involuntary movements, although neurologic and systemic manifestations of the disorder varied considerably between individual patients, even within the same family.

Use of a thick-film capillary column for the analysis of organic acids in body fluids

An improved method for the identification and quantification of organic acids in body fluids employing capillary gas chromatography-mass spectrometry has been developed. A thick-film capillary column, that combines the properties of a capillary column with those of a megabore column, has been successfully introduced into an existing method. Analysis over a concentration range from 1 mumol/l to 500 mumol/l body fluid is possible. This permits the assay of samples that are usually obtained in small volumes, e.g. cerebrospinal fluid.

Transport of the biotin dietary derivative biocytin (N-biotinyl-L-lysine) in rat small intestine

BACKGROUND

Biocytin is an important end product of intraluminal digestion of dietary protein-bound biotin. Limited studies are available regarding the ability of the small intestine to transport biocytin and about the mechanism involved. The aim of the present study was to delineate these issues.

METHODS

Transport of [3H]-biocytin was examined using everted sacs from rat intestine.

RESULTS

Mucosal-to-serosal transport of low (0.022 mumol/L) and high (5 mumol/L) concentrations of biocytin were linear for up to 20 minutes of incubation. Transport of biocytin as a function of concentration (0.022-5 mumol/L) was linear (r = 0.99) and occurred at a rate of 22,062 fmol.g tissue (wet wt)-1.15 min-1. Addition of high concentrations of unlabeled biocytin, biotin, biotin methyl ester, and lysine did not cause a significant inhibition of the transport of [3H]-biocytin. Furthermore, transport of biocytin was independent of Na+ concentration, pH, energy, and temperature. Compared with transport of equimolar concentrations of free biotin, transport of biocytin (0.022 mumol/L) was significantly lower in both the jejunum and the ileum.

CONCLUSIONS

(1) Biocytin transport in rat intestine is lower than that of free biotin and occurs via simple physical diffusion. (2) In the rat, efficient absorption and optimal bioavailability of dietary protein-bound biotin necessitates its conversion to free biotin.

An unusual presentation of medium-chain acyl coenzyme A dehydrogenase deficiency

OBJECTIVE

To report an atypical presentation of medium-chain acyl Coenzyme A dehydrogenase deficiency in a 13-year-old girl with hyperammonemic encephalopathy and orotic aciduria meeting the accepted criteria for diagnosis of a female heterozygous for ornithine transcarbamylase deficiency.

DESIGN

Case report and definitive biochemical testing.

SETTING

Children's hospital and university laboratory.

PARTICIPANT

One teenager.

INTERVENTIONS

Diagnosis and treatment with carnitine.

MEASUREMENTS/MAIN RESULTS

Assay ornithine transcarbamylase deficiency had normal results. The diagnosis was confirmed by DNA analysis, which revealed homozygosity for prevalent mutation (the adenine to guanine transition at position 985).

CONCLUSIONS

Patients with a clinical diagnosis of Reye's syndrome have, in general, an inborn error of metabolism. Medium-chain acyl Coenzyme A dehydrogenase deficiency and other disorders of fatty acid oxidation may present long after infancy. They may mimic the presentation of defects in the urea cycle.

Hawkinsinuria in two families

Hawkinsinuria, a disorder of tyrosine metabolism has been documented in two families in the United States, in one of which there was clear evidence of autosomal dominant inheritance. Metabolic acidosis and failure to thrive appear to be confined to infancy. Tyrosyl metabolites and 5-oxoproline are also found only in infancy, while 4-hydroxycyclohexylacetic acid was present only with time. The disease may be detected by organic acid analysis or by staining an electropherogram for sulfur containing compounds.

Biochemical investigation of a Brazilian patient with a defect in mitochondrial acetoacetylcoenzyme-A thiolase

A case report of 3-ketothiolase deficiency due to a defect of mitochondrial acetoacetyl-CoA thiolase protein in a Brazilian boy and its biochemical investigation is presented. The child had moderate generalized hypotonia, EEG alterations and crises of metabolic acidosis following infections. Hypotonia and EEG abnormalities disappeared with a low protein diet, and physical and mental development are normal. Urinary organic acid excretion was typical of 3-ketothiolase deficiency, showing consistently high levels of 2-methyl-3-hydroxybutyric acid and tiglylglycine. Activation of acetoacetyl-CoA thiolase activity by potassium (K) ion in cultured fibroblasts was not observed, demonstrating the lack of activity of mitochondrial acetoacetyl-CoA thiolase. In addition, the signal for the mitochondrial acetoacetyl-CoA thiolase protein was undetectable in the immunoblot analysis. In the pulse-chase experiments, the signal for mitochondrial acetoacetyl-CoA thiolase was detected after a 1-h pulse but not after a 24-h chase. These results indicate that the deficiency was caused by an unstable mitochondrial acetoacetyl-CoA thiolase protein.

Primary cultures of astrocytes from rat as a model for biotin deficiency in nervous tissue

The activities and biotin-dependence of the three mitochondrial biotin-dependent carboxylases: pyruvate carboxylase, propionyl CoA carboxylase, and beta-methylcrotonyl CoA carboxylase of primary culture of astrocytes have been examined. An increase of the three mitochondrial carboxylase activities was observed during cell growth, as was the case for developing rat brain. Mitochondrial carboxylase activities from 3-wk-old primary cultures of astrocytes were higher than those in the neonatal rat brain. When astrocytes were grown in a 10% serum-enriched medium supplemented with avidin to bind biotin, the mitochondrial carboxylase activities were reduced to 15% of control value. Consistent with these results, after 3 wk in culture, the 3-hydroxyisovaleric acid concentration in the growth medium was tenfold higher than the controls. In this culture condition, cellular growth and the nonbiotin-dependent enzyme, glutamine synthetase, were not modified with respect to control. Primary cultures from newborn rat brain hemispheres are suggested as an experimental approach to the study of biotin deficiency in nervous tissue.

3-Methylglutaconic aciduria: a marker for as yet unspecified disorders and the relevance of prenatal diagnosis in a 'new' type ('type 4')

The Mendelian disorder known as 3-methylgutaconic aciduria (McKusick 250950) gives evidence of allelic and locus heterogeneity. Type 1 has a mild clinical phenotype and confirmed 3-methylgutaconyl-CoA hydratase deficiency; inheritance is autosomal recessive. Other forms have major clinical manifestations and subdivide into X-linked (type 2), a form in Iraqi Jews with optic atrophy (so-called type 3); and untyped (putative autosomal recessive) forms without identified enzyme defects. In the latter, 3-methylglutaconic aciduria may simply be a marker for another metabolic disorder. We describe a male proband with 3-methylglutaconic aciduria designated here as 'type 4' (autosomal recessive, with severe psychomotor phenotype and cerebellar dysgenesis). He is the offspring of Italian consanguineous parents. Born with congenital malformations, he has been followed for 18 years, showing profound developmental delay and cerebellar dysgenesis. Measures of hydratase activity in cultured fibroblasts from the proband and 11 additional patients (two with type 1 disease, 9 with either type 2 or an unspecified form) revealed deficient enzyme activity in type 1 cases and normal activity in the proband and the other 11 cases. Two of the untyped cases probably have 3-methylglutaconic aciduria of the type described here. Prenatal diagnosis in the form described here may be feasible by analysis of amniotic fluid metabolites in pregnancies at risk if the mother does not entirely remove elevated concentrations. A female sibling of the proband had normal metabolite values in amniotic fluid. Postnatal follow-up confirmed absence of the disease. We give the normal values for amniotic fluid and results on these additional fetuses at risk (none affected).

A new immunochemical assay for biotin

A double antibody technique has been developed to separate free biotin from bound biotin after competitive binding of [3H]biotin and unlabelled biotin to avidin. Antiavidin goat antibody was added followed by the addition of antigoat IgG antibody linked to agarose. Centrifugation separated the free biotin from the biotin bound to the avidin complex. The method was suitable for the detection of the amounts of biotin contained in 100-200 microliters of plasma or 5-10 microliters of urine. Normal values for the concentration of biotin in plasma and urine determined by this assay were 1.27 +/- 0.67 nmol/l and 49.1 +/- 35.7 mumol/mol creatinine, respectively.

3-Hydroxyisobutyric aciduria: an inborn error of valine metabolism

3-Hydroxyisobutyric aciduria, a disorder of valine metabolism, has been found in a boy in whom the clinical picture was that of a typical organic acidemia with repeated episodes of ketoacidosis requiring admission to hospital and parenteral fluid therapy, along with impressive failure to thrive and chronic lactic acidemia. The excretion of 3-hydroxyisobutyric acid ranged from 170 to 390 mmol/mol of creatinine. The administration of valine increased this to 18,700 mmol/mol of creatinine and reproduced the clinical picture of ketoacidosis. Concentrations of free carnitine were low, and esterified carnitine was elevated. Treatment with carnitine and a diet restricted in protein appeared to be beneficial.

Metabolism of 1-13C-propionate in vivo in patients with disorders of propionate metabolism

Metabolism of propionate in human subjects was studied using bolus administration of 1-13C-propionate i.v. or orally. The study population consisted of five patients with propionic acidemia (PA), eight with methylmalonic acidemia (MMA; four responsive to vitamin B12), one each with multiple carboxylase deficiency and transcobalamin-II deficiency, and five healthy volunteers. Concentrations of 1-13C-propionate were measured in blood in three patients with PA, two with MMA, and two controls. Breath samples were obtained at intervals during 3 h after the dose, isotopic enrichment of 13CO2 was measured, and the cumulative percentage of recovery of 13C was calculated from the individual's predicted resting energy expenditure. Recovery of 13CO2 and half-time of 1-13C-propionate in PA were significantly less than normal. The same parameters in MMA were below normal, but significantly greater than in PA. Recovery of 13CO2 was well correlated with clinical severity in PA, but did not correlate in MMA. Differences between MMA and PA may indicate different distribution of propionate pools, differences in inducibility of residual enzyme activities, or an alternate pathway for decarboxylation of propionate available in MMA but not PA. Only one patient with PA demonstrated increased 13CO2 production during biotin treatment. In a B12-responsive MMA patient, no differences were noted within 2 d of initiating treatment with B12, but there was an increase in 13CO2 production after 4 mo. Recovery of 13CO2 was normal in the patient with transcobalamin-II deficiency before and after treatment with vitamin B12.(ABSTRACT TRUNCATED AT 250 WORDS)

Facts and artefacts in mevalonic aciduria: development of a stable isotope dilution GCMS assay for mevalonic acid and its application to physiological fluids, tissue samples, prenatal diagnosis and carrier detection

A stable isotope dilution assay using D3-mevalonic acid was developed and applied to the study of mevalonic aciduria. The method also appears to be suitable for the evaluation of different therapeutic regimens in patients with hypercholesterolemia. Mevalonic acid was isolated by liquid partition chromatography and quantified as the underivatized lactone by means of ammonia chemical ionization selected ion monitoring capillary gas chromatography-mass spectrometry. In heterozygotes there was significantly greater urinary excretion of mevalonic acid, while the range of enzymatic activity of mevalonate kinase showed an overlap with that of controls. The analysis of amniotic fluids of two pregnancies at risk for mevalonic aciduria showed a 3277-fold elevation as compared to controls in the first case, diagnostic of an affected fetus, and a normal value in the second one. Mevalonic acid concentration was much increased in tissues of the affected and aborted fetus. Concentrations ranged from 840 to 1120 mumol/kg in various tissues and were as high as 1810 mumol/kg in brain. Concentrations in control fetal tissues were approximately 1 mumol/kg.

Endothelial heterogeneity in the chick wing bud: a morphometric study

The microvascular endothelium of the chick wing bud at stages 22, 27, and 32 was evaluated by ultrastructural morphometry. The rationale for this study is based on the hypothesis that endothelial cells exhibit variation in structure and function during cytodifferentiation. The microvessels had a luminal diameter range such that they were classified as capillaries. The thin continuous endothelium was devoid of a basal lamina. The endothelium had a very small number of plasmalemmal vesicles; vacuoles were however present for all stages and in some cases were abundant. The temporal findings were that endothelial cell thickness increases, plasmalemmal vesicle densities decrease, and the densities of cytoplasmic vacuoles increase. The spatial results were that endothelial cells in proximal regions of the limb have a greater thickness, contain fewer vesicles and have more vacuoles than those in distal regions. In general, these results indicate that endothelial ultrastructural heterogeneity occurs within a 3 1/2 day time-span of wing bud development. The discussion considers the results with regard to recent reports on endothelial cell heterogeneity.

Urinary excretion of 2-methylacetoacetate, 2-methyl-3-hydroxybutyrate and tiglylglycine after isoleucine loading in the diagnosis of 2-methylacetoacetyl-CoA thiolase deficiency

The concentrations of 2-methylacetoacetate, 2-methyl-3-hydroxybutyrate and tiglylglycine were determined by gas chromatography-mass spectrometry in urine collected before and for 8 h after loading with 100 mg of isoleucine per kg of body weight. The sum of 2-methylacetoacetate and 2-butanone, a decarboxylation product, was determined as the 2-butanone dinitrophenylhydrazone derivative. Substantial increases in each compound were encountered in a patient with a documented defect of 2-methylacetoacetyl-CoA thiolase. Increased quantities of 2-methyl-3-hydroxybutyrate and tiglylglycine were also found in four children with clinical symptoms similar to those associated with 2-methylacetoacetyl-CoA thiolase deficiency but in whom the activity of the enzyme was found to be normal. The concentration of 2-methylacetoacetate plus 2-butanone in the urine increased after an isoleucine load only in the patient with 2-methylacetoacetyl-CoA thiolase deficiency.

3-Oxothiolase activities and [14C]-2-methylbutanoic acid incorporation in cultured fibroblasts from 13 cases of suspected 3-oxothiolase deficiency

Cultured fibroblasts from 13 patients with organic aciduria suggesting 3-oxothiolase deficiency were studied by measuring first the capacity of the isoleucine degradative pathways in whole cells, as the incorporation of 1-[14C]-2-methylbutanoic acid into macromolecules, and, second, the activity of 3-oxothiolase in cell homogenates using specific 3-oxoacyl-CoA substrates to identify the different enzymes. Nine patients showed low incorporation by the macromolecular labeling assay, as well as deficiency of 2-methylacetoacetyl-CoA thiolase. In this group of patients, low activity by the macromolecular labeling assay was associated with clinically severe symptoms, and vice versa. Two patients showed reduced macromolecular labeling, but apparently normal 3-oxothiolase. Finally, two patients showed normal activities by either test, the reason for their particular organic aciduria being unknown. In conclusion, occurrence of urinary 2-methyl-3-hydroxybutyric acid and/or tiglyglycine is not an unequivocal indicator of the absence of the thiolase that metabolizes 2-methylacetoacetyl-CoA. Measurement of 1-[14C]-2-methylbutanoic acid incorporation in cultured fibroblasts adds important information in studying possible defects of the isoleucine catabolic pathway.

Enzymatic diagnosis of 3-hydroxy-3-methylglutaryl-CoA lyase deficiency with high-performance liquid chromatography

A new non-radiochemical method for determination of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) lyase is described. Acetyl-CoA, the product of the enzymatic reaction, is separated from the substrate by high-performance liquid chromatography and is quantified. The mean 3-hydroxy-3-methylglutaryl-CoA lyase activity in control fibroblasts was 7.8 +/- 2.1 (SD) nmol/min per mg protein, and its apparent Km value was 77.8 +/- 14.3 microM (R/S mixture) with a calculated Vmax of 12.4 +/- 2.2 nmol/min per mg protein. Using this method, we could easily differentiate a patient with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency from control subjects.

An improved chemical ionization assay for mevalonic acid

The determination of mevalonic acid by gas chromatography/mass spectrometry (GC/MS) is complicated by poor extractability and multiple product formation. Reliable quantification down to physiological levels was achieved by isolating mevalonic acid by liquid partition chromatography and quantifying the underivatized lactone by means of ammonia chemical ionization, selected ion monitoring, capillary GC/MS. (2H3)mevalonic acid served as the internal standard. The method appears to be suitable for the study of mevalonic aciduria as well as the evaluation of different therapeutic regimens in patients with hypercholesterolaemia.

[Pre- and postnatal diagnosis of organoacidopathies]

Organoacidopathies are the most common life-threatening inborn errors of metabolism presenting acutely in the neonatal period. Early diagnosis rests on a high degree of suspicion. Clinical and laboratory findings are often nonspecific and can be misinterpreted. We present an algorithm for a quick and comprehensive diagnosis of these disorders using commonly available parameters. Different methods for the prenatal diagnosis of organoacidopathies are discussed and our experience with over 150 cases presented. The method of choice is the precise quantification of elevated levels of metabolites in amniotic fluid obtained by amniocentesis at 12-18 weeks of pregnancy. Quantification is best done by stable isotope dilution analysis with the addition of the labelled metabolite to the amniotic fluid. A positive prenatal diagnosis allows a decision of the family for a termination of pregnancy or the immediate institution of therapy after birth. The conduction of a prenatal diagnosis requires the knowledge of the exact diagnosis of a previously affected child.

Pyridoxine-unresponsive homocystinuria with an unusual clinical course

Progressive premature atherosclerosis and associated thromboembolic complications are the main causes of morbidity and mortality in patients with homocystinuria. However, thrombosis is rarely the predominant or presenting manifestation leading to the diagnosis of homocystinuria. We report on an otherwise asymptomatic teenage boy of normal intelligence who had a superior sagittal sinus thrombosis documented by CT and MRI scans. He presented with pneumothoraces, papilledema, and transient right hemiparesis. He subsequently developed empyema and necrotizing pneumonia as well as deep venous thromboses. The diagnosis of pyridoxine-unresponsive homocystinuria was made on the basis of clinical chemistry analyses, enzyme assay, and clinical trial. He has remained symptom-free under treatment with betaine and methionine restriction. We suggest that there exists a subset of patients with pyridoxine-unresponsive homocystinuria who are at risk for thromboembolism, but who may remain undiagnosed because of an otherwise mild clinical course.