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.

3-Hydroxy-3-methylglutaryl coenzyme A reductase activity in cultured fibroblasts from patients with mevalonate kinase deficiency: differential response to lipid supplied by fetal bovine serum in tissue culture medium

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity was measured in extracts of cultured fibroblasts derived from patients with mevalonate kinase deficiency (MKD). For six patients studied, the mean activity of 63.3 +/- 41.1 pmol/min-mg protein (+/- 1 SD, range 37.7-146.2) was significantly higher than the mean value in three control fibroblast lines of 11.1 +/- 3.5 (+/- 1 SD, range 8.0-14.9). These values were obtained using cells subcultured in medium supplemented with 10% fetal bovine serum (FBS) 21 h prior to assay. When cells were deprived of cholesterol by subculturing for 21 h in delipidated FBS, the mean value for patient cells was increased to 230.8 +/- 78.5 pmol/min-mg protein (range 130.9-333.8) as compared to 109.5 +/- 47.1 (range 78.0-163.6) for controls. The activity of HMG-CoA synthase in extracts of fibroblasts derived from the patients was not elevated. The mevalonic acid concentration in the surrounding culture medium was assessed by stable isotope dilution assay. For five patients, the mean concentration in medium containing FBS was 0.92 +/- 0.37 microM (+/- 1 SD, range 0.46-1.48) in contrast to 1.24 +/- 0.83 microM (range 0.46-2.54) for cells subcultured in delipidated FBS. The mean value for three control fibroblast lines was 0.22 +/- 0.12 microM (+/- 1 SD, range 0.11-0.35) for cells subcultured in FBS as compared to 0.01 +/- 0.01 microM (range 0.0-0.01 microM) for cells sucultured in delipidated FBS.(ABSTRACT TRUNCATED AT 250 WORDS)

[3-hydroxy-3-methylglutaraturia. Clinical aspects, follow-up and therapy in a young child]

This is a report of an infant with 3-hydroxy-3-methylglutaryl-CoA-lyase deficiency. During infancy vomiting and feeding difficulties had been found repeatedly. Nutrition consisted in a mixture of one third of milk diluted with two thirds of water. Shortly before admission a change to whole milk had taken place. The one year old girl was admitted to the hospital because of vomiting and diarrhoea. Liver was enlarged and consciousness reduced. There was acidosis, hypoglycemia and an elevation of the transaminases. The typical pattern of organic acids in urine and dicarboxylic aciduria was pathognomonic. The diagnosis was proved by a deficiency of 3-hydroxy-3-methylglutaryl-CoA-lyase in fibroblasts. A protein and fat restricted diet, but also carnitine supplement was introduced. With the exception of severe hypoglycemia seizures on one morning the more than 2 1/2 year old girl is developed normally. It is of importance for future to avoid hypoglycemia after fasting, infections diseases or stress. The possible impairment of pancreatic function even in a normal clinical condition with normal values of transaminases is especially pointed out.

Stable isotope dilution analysis of 4-hydroxybutyric acid: an accurate method for quantification in physiological fluids and the prenatal diagnosis of 4-hydroxybutyric aciduria

A quantitative assay for 4-hydroxybutyric acid was developed using D6-4-hydroxybutyric acid as an internal standard. 4-Hydroxybutyric acid was isolated by liquid chromatography and the amount quantified by selected ion monitoring, ammonia chemical ionization gas chromatography/mass spectrometry of the trimethylsilyl derivatives. The concentrations of 4-hydroxybutyric in control physiological fluids were: 2.64 +/- 3.46 mmol mol-1 creatinine in urine, 1.09 +/- 2.87 mumol l-1 in plasma, 0.98 +/- 1.17 mumol l-1 in cerebrospinal fluid and 1.28 +/- 0.47 mumol l-1 in amniotic fluid. The concentration of 4-hydroxybutyric acid in the amniotic fluid from a pregnancy at risk for 4-hydroxybutyric aciduria was 2.30 mumol l-1, indicating an unaffected fetus. The stable isotope dilution assay of 4-hydroxybutyric acid in physiological fluid samples is a rapid, sensitive and accurate method for quantification, as well as a valuable technique for the prenatal diagnosis of 4-hydroxybutyric aciduria.

3-Hydroxy-3-methylglutaryl-CoA lyase deficiency as detected by radiochemical assay in cell extracts by thin-layer chromatography, and identification of three new cases

In this rapid radiochemical assay for 3-hydroxy-3-methylglutaryl-coenzyme A lyase (I) activity in cell extracts, DL-3[glutaryl-3-14C]hydroxy-3-methylglutaryl-coenzyme A is used as substrate and the radiochemical product, [3-14C]acetoacetic acid, is converted to the more stable [3-14C]-3-hydroxybutyric acid in the presence of added NADH and 3-hydroxybutyrate dehydrogenase. Substrate and product are separated and quantified by thin-layer chromatography on cellulose (solvent system: butanol/water/formic acid, 77:13:10 by vol). All reagents for the assay are commercially available. No detailed column chromatography or spectrophotometry is required. Thus the assay is suited for any clinical laboratory. Using this procedure, we studied cultured fibroblasts or lymphocytes isolated from whole blood from five patients in whom the urinary organic acid profile was suggestive of deficiency of I. Three patients had less than or equal to 18% of control I activity in fibroblast or lymphocyte extracts. The other two had activity within the normal range. In one of the latter cases, urinary excretion of three of the characteristic acids disappeared with age, and 3-hydroxyisovaleric acid excretion was within normal limits. The other case presented with urinary excretion of moderate amounts of all four metabolites and the characteristic absence of urinary ketone bodies. Evidently, confirmatory enzyme studies should be undertaken, even when the profile of urinary organic acids appears definitive for this deficiency.

3-Hydroxy-3-methylglutaryl-CoA lyase deficiency as detected by radiochemical assay in cell extracts by thin-layer chromatography, and identification of three new cases

In this rapid radiochemical assay for 3-hydroxy-3-methylglutaryl-coenzyme A lyase (I) activity in cell extracts, DL-3[glutaryl-3-14C]hydroxy-3-methylglutaryl-coenzyme A is used as substrate and the radiochemical product, [3-14C]acetoacetic acid, is converted to the more stable [3-14C]-3-hydroxybutyric acid in the presence of added NADH and 3-hydroxybutyrate dehydrogenase. Substrate and product are separated and quantified by thin-layer chromatography on cellulose (solvent system: butanol/water/formic acid, 77:13:10 by vol). All reagents for the assay are commercially available. No detailed column chromatography or spectrophotometry is required. Thus the assay is suited for any clinical laboratory. Using this procedure, we studied cultured fibroblasts or lymphocytes isolated from whole blood from five patients in whom the urinary organic acid profile was suggestive of deficiency of I. Three patients had less than or equal to 18% of control I activity in fibroblast or lymphocyte extracts. The other two had activity within the normal range. In one of the latter cases, urinary excretion of three of the characteristic acids disappeared with age, and 3-hydroxyisovaleric acid excretion was within normal limits. The other case presented with urinary excretion of moderate amounts of all four metabolites and the characteristic absence of urinary ketone bodies. Evidently, confirmatory enzyme studies should be undertaken, even when the profile of urinary organic acids appears definitive for this deficiency.

3-Methylglutaconyl-CoA hydratase, 3-methylcrotonyl-CoA carboxylase and 3-hydroxy-3-methylglutaryl-CoA lyase deficiencies: a coupled enzyme assay useful for their detection

A coupled assay has been developed using 3-methylcrotonyl-CoA and NaH14CO3 which permits the detection of deficiencies of 3-methylcrotonyl-CoA carboxylase, 3-methylglutaconyl-CoA hydratase and 3-hydroxy-3-methylglutaryl CoA-lyase. The products of the reaction were analyzed by high performance liquid chromatography. Using this method the site of the defect was documented in a patient with deficiency of 3-methylcrotonyl-CoA carboxylase, 2 patients with deficiency of 3-methyl-glutaconyl-CoA hydratase, and 2 patients with deficiency of 3-hydroxy-3-methyl-glutaryl-CoA lyase.

Metabolism of [U-14C]-4-hydroxybutyric acid to intermediates of the tricarboxylic acid cycle in extracts of rat liver and kidney mitochondria

The metabolism of [U-14C]-4-hydroxybutyric acid (GHB) was investigated in sonicates of mitochondria of rat heart, kidney and liver. The conversion of this precursor to 14C-organic acids was monitored and quantified by sequential liquid-partition chromatography on hydrated columns of silicic acid using a concave-upward gradient of 2-methylbutan-2-ol in chloroform. Sonicates of liver and kidney mitochondria, but not heart, readily converted [U-14C]-GHB to 14C organic acids via a pathway of conversion to 14C-succinic acid, followed by further metabolism through the tricarboxylic acid cycle. This conversion was facilitated by exogenous NAD+ and NADP+. No evidence for the beta-oxidation of GHB was obtained in any of the mitochondrial sonicates. Studies with exogenous non-labelled succinic semialdehyde indicated that this compound was an intermediate in the conversion of GHB to succinic acid.

Mevalonate kinase in lysates of cultured human fibroblasts and lymphoblasts: kinetic properties, assay conditions, carrier detection and measurement of residual activity in a patient with mevalonic aciduria

An assay has been developed for the measurement of mevalonate kinase activity in extracts of cultured human fibroblasts and lymphoblasts. Individual elements of the assay were investigated in order to achieve optimum conditions. Apparent Michaelis constants (KMapp) for the substrates mevalonic acid and adenosine-5'-triphosphate were 22 +/- 10 mumol/l and 0.42-0.53 mmol/l, respectively, in lysates of control fibroblast lines. The same values in lysates of a control lymphoblast line were 17 mumol/l and 0.23 mmol/l, respectively. Mevalonate kinase activity in extracts of cultured fibroblasts derived from 6 control individuals was 3.24 +/- (SD) 0.91 nmol/min/mg protein. The activity in extracts of fibroblasts derived from a patient with mevalonic aciduria was 0.15 +/- 0.10 nmol/min/mg protein, approximately 5% of the control mean. The parents and brother of the patient displayed mevalonate kinase activities in fibroblast extracts approximating 38-42% of the control mean. Substantially higher mevalonate kinase activity was documented in extracts of cultured lymphoblasts. When assayed on various occasions, the mean activity of mevalonate kinase in extracts of lymphoblasts derived from the parents, brother and maternal grandmother of the patient ranged from 27 to 32% of the mean activity of 9.8 +/- (SD) 3.4 nmol/min/mg protein measured in a parallel control lymphoblast line, while the mean activity in a maternal and paternal uncle approximated 65-89% of the same control mean. The mean activity in extracts of lymphoblasts derived from the patient approximated 2% of the control mean. The data suggest that the parents, brother and maternal grandmother are carriers of the defective gene responsible for mevalonate kinase deficiency, consistent with an autosomal recessive mode of inheritance.

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: review of 18 reported patients

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMG-CoA lyase) is an inborn error of leucine catabolism which often leads to life-threatening illness in the neonatal period. The cardinal clinical features include severe infantile hypoglycemia, metabolic acidosis, hepatomegaly, lethargy or coma and apnea. Hyperammonemia is variable. There is a characteristic absence of ketosis. Considerable heterogeneity has been observed in clinical and biochemical presentation. Acute episodes of illness have been mistaken for Reye syndrome. The pattern of organic acids in the urine includes large amounts of 3-hydroxy-3-methylglutaric, 3-methyl-glutaconic, 3-methylglutaric and 3-hydroxyisovaleric acids. Smaller, but appreciable levels of glutaric, adipic and other dicarboxylic acids may also be excreted in the urine. Lactic acid may be present in sizable amounts at times of acute illness. The primary defect is a deficiency of 3-hydroxy-3-methylglutaryl-coenzyme A lyase, a key enzyme in the cycle of ketogenesis.

Mevalonate kinase deficiency in a child with cerebellar ataxia, hypotonia and mevalonic aciduria

Mevalonate kinase deficiency has been documented in an 8-year-old child who presented with cerebellar ataxia, hypotonia and mevalonic aciduria. The activity of mevalonate kinase in extracts of cultured skin fibroblasts derived from the patient was approximately 2% of the mean value for controls. Family studies were carried out on the mother, the father and a sister, all of whom were clinically well. Mevalonate kinase activity in extracts of cultured skin fibroblasts and transformed lymphoblasts derived from the parents of the patient were 43%-52% of the mean control values. These data are consistent with an autosomal recessive mode of inheritance for mevalonate kinase deficiency.

Conservation of central nervous system glutaryl-coenzyme A dehydrogenase in fruit-eating bats with glutaric aciduria and deficient hepatic glutaryl-coenzyme A dehydrogenase

The adult fruit-eating bat, Rousettus aegypticus, excretes massive amounts of glutaric acid in the urine (20-70 mumol/mg creatinine) comparable to those of humans affected with the inherited metabolic disorder, glutaric aciduria type I. Glutaric acid was quantified by sequential liquid partition chromatography and gas chromatography. Oral loading with the amino acid precursors of glutaric acid, L-lysine and L-tryptophan, resulted in significant increases in glutaric acid excretion above the base-line values. Glutaryl-CoA dehydrogenase activity was assayed in adult bat tissues and compared with the same tissues in the rat using methods of 14CO2 evolution from 1,5-[14C]glutaryl-CoA. A severe deficiency of glutaryl-CoA dehydrogenase activity was found in the bat liver and kidney, whereas brain and spinal cord levels were similar to those in the rat. Reverse phase high performance liquid chromatography analysis of the metabolites in the assay mixture showed negligible hydrolysis of [14C]glutaryl-CoA to free [14C]glutaric acid and complete conversion of the product [14C]crotonyl-CoA to 3-hydroxy[14C]butyryl-CoA. The adult bat, with its huge glutaric acid excretion and deficient liver glutaryl-CoA dehydrogenase, metabolically mimics patients affected with glutaric aciduria type I. The bat does not, however, display the neurologic manifestations seen in patients. This may be explained by conservation of glutaryl-CoA dehydrogenase activity in the central nervous system of the bat.

Oxidation of [U-14C]succinic semialdehyde in cultured human lymphoblasts: measurement of residual succinic semialdehyde dehydrogenase activity in 11 patients with 4-hydroxybutyric aciduria

The oxidation of [U-14C]succinic semialdehyde to 14CO2 has been investigated in cultured lymphoblasts to develop a whole cell assay for succinic semialdehyde dehydrogenase. We have previously demonstrated deficiency of this enzyme in extracts of white cells derived from 13 patients with 4-hydroxybutyric aciduria. Major goals were the demonstration of greater residual succinic semialdehyde dehydrogenase activity in patient cell lines and the better representation of physiology in vivo. In 18 control lymphoblast lines, the conversion of [U-14C]succinic semialdehyde to 14CO2 was 1579 +/- 310 dpm. The mean value in lymphoblasts derived from 11 patients with deficiency of succinic semialdehyde dehydrogenase was 112 +/- 36 dpm approximating 7% of the mean control value. Analysis of organic acids produced from [U-14C]succinic semialdehyde in control lymphoblasts indicated that 14CO2 emanated from the tricarboxylic acid cycle; the major metabolic products were succinic and lactic acids. In the presence of 5mM malonic and 2-propylpentanoic (valproic) acids, 14CO2 production in a control lymphoblast line was decreased by 68 and 45%, respectively. The whole cell assay is less laborious than our previously described assay employing cell extracts, and the general trend was the demonstration of higher residual levels of activity for lymphoblasts derived from patients.

3-Methylglutaconic aciduria: a phenotype in which activity of 3-methylglutaconyl-coenzyme A hydratase is normal

3-Methylglutaconic aciduria has been found in two distinct syndromes. In one there is deficient activity of 3-methylglutaconyl coenzyme A hydratase, and the only clinical manifestation observed has been retardation of speech development. In the other, which includes a majority of the patients studied, we document that the activity of this enzyme in fibroblast extracts is normal. The phenotype of this disorder is one of profound neurological impairment with retarded psychomotor development, hypotonicity and/or spasticity, convulsions or EEG abnormalities, and sensorineural changes in the eye and ear.

4-Hydroxybutyric aciduria in a patient without ataxia or convulsions

A child presenting with mild psychomotor retardation, hypotonia, microcephaly and hyperkinesis is described. Urinary organic acid analysis by combined gas chromatography-mass spectrometry revealed 4-hydroxybutyric aciduria. Succinic semialdehyde dehydrogenase activity in extracts of white cells derived from the patient was less than 10% of control values.