3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: report of five new patients

Five new patients are reported and the pathogenesis of the hypoglycaemia without ketogenesis is discussed. This report extends a recent review.

3-Hydroxy-3-methylglutaric aciduria: response to carnitine therapy and fat and leucine restriction

A female infant, born to first cousin parents, lapsed into coma with severe metabolic acidosis on day three of life. The gas chromatographic/mass spectrometric urinary organic acid profile showed marked elevation of the leucine metabolites 3-hydroxy-3-methylglutaric, 3-methylglutaconic, 3-methylglutaric and 3-hydroxy-isovaleric acids. Less than 5% of the normal activity of the enzyme 3-hydroxy-3-methylglutaryl CoA lyase was detected in cultured skin fibroblasts. The patient's total and free carnitine was initially low but rose to normal levels after placing her on DL-carnitine (100 mg kg-1 d-1). On a diet providing 87 mg kg-1 d-1 of leucine and only 25% of total calories as fat and 2 g kg-1 d-1 protein, the concentration of the urinary organic acids fell markedly. She is now 15 months old with normal growth and development. This regimen appears effective in the early treatment of 3-hydroxy-3-methylglutaric aciduria.

Atypical presentation and neuropathological studies in 3-hydroxy-3-methylglutaryl-CoA lyase deficiency

A 6 1/2-month-old male offspring of consanguineous Egyptian parents was first seen because of fever, somnolence, vomiting, right focal motor seizures, right hemiparesis, elevated transaminase levels, hyperammonemia, and acidosis. A computed tomographic scan of the head suggested swelling of the left cerebral hemisphere, and an electroencephalogram indicated left frontotemporal abnormalities, but brain biopsy demonstrated diffuse white matter spongiosis and gliosis. Subsequently, urine organic acid analysis and enzyme assays were diagnostic of 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency.

Mevalonic aciduria--an inborn error of cholesterol and nonsterol isoprene biosynthesis

A two-year-old boy presented with severe failure to thrive, developmental delay, anemia, hepatosplenomegaly, central cataracts, and dysmorphic features. Quantitative analyses of urinary organic acids revealed massive excretion of mevalonic acid, a metabolic precursor of cholesterol and nonsterol isoprenes: 46,000 to 56,200 mmol per mole of creatinine, as compared with 0.2 to 0.3 mmol per mole in normal children. The mevalonic acid concentration in plasma was also greatly increased at 440 mumol per liter (normal, less than 0.05). The activity of mevalonate kinase, the enzyme that catalyzes the first step in mevalonate metabolism, was severely deficient in the patient's fibroblasts, lymphocytes, and lymphoblasts. In the subsequent pregnancy of the patient's mother, gas chromatography-mass spectrometry demonstrated a marked elevation of mevalonic acid in the mother's urine and a 3000-fold elevation, as compared with control levels in the amniotic fluid, suggesting that the fetus was affected. The diagnosis was confirmed by demonstration of the deficiency of mevalonate kinase in amniocytes and ultimately in liver from the abortus. Intermediate activities of the enzyme in both parents indicated an autosomal recessive mode of inheritance. These observations identify an inherited disorder of cholesterol and nonsterol isoprene biosynthesis in humans.

Activity of biotin-dependent and GABA metabolizing enzymes in chorionic villus samples: potential for 1st trimester prenatal diagnosis

We have documented the presence of five mitochondrial enzymes in samples of chorionic villus tissue and measured the levels of activity. Three of the enzymes catalyse biotin-dependent reactions. These are propionyl-CoA carboxylase, 3-methylcrotonyl-CoA carboxylase and pyruvate carboxylase. The other enzymes, 4-aminobutyric acid aminotransferase and succinic semialdehyde dehydrogenase, are involved in the degradation of the central inhibitory neurotransmitter GABA. Distinct diseases in which there is deficiency of each of these enzymes have been documented in man. Significant levels of activity were observed for all five enzymes in chorionic villus tissue. This methodology should permit early prenatal diagnosis of deficiencies of these enzymes by chorionic villus biopsy in the first trimester.

Deficiency of 3-methylglutaconyl-coenzyme A hydratase in two siblings with 3-methylglutaconic aciduria

We studied two patients with 3-methylglutaconic aciduria in order to determine the molecular defect. A new assay for 3-methylglutaconyl-coenzyme A (CoA) hydratase has been developed in which the substrate, [5-14C]3-methylglutaconyl-CoA, was synthesized using 3-methylcrotonyl-CoA carboxylase purified from bovine kidney. In this assay the products of the reaction are isolated by reverse-phase high performance liquid chromatography and the rates of conversion from substrate are measured. The Michaelis constant for 3-methylglutaconyl-CoA in normal fibroblasts was 6.9 mumol/liter. The mean activity of 3-methylglutaconyl-CoA hydratase in control fibroblasts was 495 pmol/min per mg protein. In the two patients the values were 11 and 17 pmol/min per mg protein, or 2-3% of normal.

Properties of succinic semialdehyde dehydrogenase in cultured human lymphoblasts

A direct assay has been developed for succinic semialdehyde dehydrogenase in sonicates of human lymphocytes and Epstein-Barr Virus transformed cultured lymphoblasts. Enzyme activity was quantified by incubating cell extracts with uniformly labeled [14C]succinic semialdehyde and monitoring the conversion to [14C]succinic acid. Radiolabeled products were separated by liquid partition chromatography on hydrated silicic acid. Kinetic properties and requirements of succinic semialdehyde dehydrogenase in lymphoblast sonicates were investigated in order to determine optimal conditions for the direct assay. Enzyme activity was stimulated by dithiothreitol, ammonium and potassium ions and 0.1% Triton X-100. The concentrations for half maximal activation by ammonium and potassium were 5.2 and 13.7 mM respectively. The mean activity of succinic semialdehyde dehydrogenase in assays in which equimolar NADP+ had been substituted for NAD+ was 19% of the activity of assays which contained NAD+. Substrate Michaelis constants were 21 and 30 microM for NAD+, and 26, 42 and 70 microM for succinic semialdehyde. The enzyme displayed a pH optimum between 8 and 9 and demonstrated a slight temperature activation between 37 degrees and 45 degrees C. A deficiency of succinic semialdehyde dehydrogenase activity was documented in cultured lymphoblasts derived from a patient with gamma-hydroxybutyric aciduria.

Demonstration of 4-aminobutyric acid aminotransferase deficiency in lymphocytes and lymphoblasts

Lysates of lymphocytes, isolated from whole blood, and Epstein-Barr virus transformed cultured lymphoblasts catalysed the transamination of 4-aminobutyric acid with 2-oxoglutaric acid as co-substrate. 4-Aminobutyric acid aminotransferase activity in lymphocyte and lymphoblast sonicates derived from 12 unrelated control individuals (6 each) was 39 +/- 19 pmol min(-1) (mg protein (-1] (mean +/- 1 SD). Activities in lysates of both types of cell derived from a Flemish patient were less than 3% of control. 4-Aminobutyric acid aminotransferase activity in sonicates derived from the parents and a healthy sibling were 15-37% of the control mean for lymphocytes and 13-20% of the control mean in lymphoblasts, respectively. Km values in a control lymphoblast sonicate were 0.63 and 0.08 mmol L(-1) for 4-aminobutyric and 2-oxoglutaric acids, respectively. These data indicate that the parents and healthy sibling are heterozygous and the patient is homozygous for a defective gene responsible for 4-aminobutyric acid aminotransferase deficiency, and that inheritance is autosomal recessive.

A child with acute pancreatitis and recurrent hypoglycemia due to 3-hydroxy-3-methylglutaryl-CoA lyase deficiency

A five-year-old-girl with a history of recurrent hypoglycemia presented with acidosis, intractable vomiting, and abdominal tenderness; the diagnosis of acute pancreatitis was made by abdominal ultrasonography and supportive biochemical studies. Urinary organic acid analysis revealed metabolites suggestive of HMG-CoA lyase deficiency, and subsequent enzyme assays of lymphocytes and fibroblasts confirmed this diagnosis. Acute pancreatitis, an uncommon condition in childhood, is seen with increased frequency in patients with Reye syndrome, a metabolic disorder with which HMG-CoA lyase deficiency may be confused. The pathogenesis of pancreatitis in Reye syndrome or in HMG-CoA lyase deficiency has not been determined.

Defective succinic semialdehyde dehydrogenase activity in 4-hydroxybutyric aciduria

Succinic semialdehyde dehydrogenase deficiency has been demonstrated in a fourth patient with 4-hydroxybutyric aciduria. Lysates of freshly isolated lymphocytes and cultured lymphoblasts of the patient had much lower than control activity in the conversion of U-14C-4-aminobutyric acid to 14C-succinic acid in an assay designed to estimate succinic semialdehyde dehydrogenase utilizing endogenous 4-aminobutyrate transaminase. Lymphocyte and lymphoblast lysates of the patient accumulated U-14C-succinic semialdehyde when incubated with U-14C-4-aminobutyric acid and NAD+ whereas none could be detected in controls. Assays using U-14C-succinic semialdehyde as substrate for succinic semialdehyde dehydrogenase in lysates of cultured lymphoblasts characterized the patient as having a severe deficiency of succinic semialdehyde dehydrogenase. The data indicate that defective activity of succinic semialdehyde dehydrogenase is responsible for 4-hydroxybutyric aciduria.

Succinic semialdehyde dehydrogenase deficiency

A coupled assay using [14C]4-aminobutyric acid and a direct assay using [14C]succinic semialdehyde have been designed to assay te activity of succinic semialdehyde dehydrogenase in a patient with 4-hydroxybutyric aciduria and family members. In the coupled assay less than 3% of control succinic semialdehyde dehydrogenase activity was found in lysates of lymphocytes isolated from whole blood of the patient. In the direct assay there was no detectable activity of the enzyme in lysates of isolated lymphocytes or cultured lymphoblasts. Results indicated the parents to be heterozygous carriers carriers of the abnormal gene, consistent with an autosomal recessive inheritance.

Genetic complementation analysis of 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency in cultured fibroblasts

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) lyase deficiency is an inherited metabolic disorder of leucine catabolism showing variability in clinical expression. We have examined the possibility of a biochemical and genetic basis for this heterogeneity by measuring the residual enzyme activities in fibroblast cultured from seven patients. The mean activity of HMG-CoA lyase was 1.1% +/- 0.3% of normal with no significant differences between the patients. Genetic complementation was studied in heterokaryons obtained by fusion with polyethylene glycol using the incorporation of 1-[14C]isovaleric acid into trichloroacetic acid precipitable material to determine the activity of the leucine catabolic pathway. Unfused cells from the patients with a deficiency of HMG-CoA lyase had incorporations of less than 5% of normal. Unfused cells from patients with isovaleric acidemia or a deficiency of 3-methylcrotonyl-CoA carboxylase also had incorporations of less than 5% of normal, and when fused with cells of patients with a deficiency of HMG-CoA lyase, gave positive complementation with an incorporation of 30% of normal. None of the fusions between the seven different lines deficient in HMG-CoA lyase resulted in increased incorporation. Thus, no evidence was obtained for biochemical or genetic heterogeneity in fibroblasts of these seven patients with a deficiency of HMG-CoA lyase that would account for their different clinical presentations.

3-Hydroxy-3-methylglutaric aciduria

3-Hydroxy-3-methylglutaric aciduria was found in a newborn infant whose parents are first cousins. The patient presented at 5 days of life with hyperammonemia, hypoglycemia, and metabolic acidosis. There was no ketonuria. Diagnosis was made by analysis of the pattern of organic acids excreted in the urine. A profound deficiency in activity of 3-hydroxy-3-methylglutaryl-coenzyme A lyase was found in cultured skin fibroblasts. The parents had intermediate levels of enzyme activity.

Enzymatic preparation of radiolabeled succinic semialdehyde

[U-14C]Succinic semialdehyde was prepared with yields of 30-40% by oxidation of purified [U-14C]4-aminobutyric acid with commercially available bovine plasma monoamine oxidase. [U-14C]Succinic semialdehyde was purified by cation-exchange chromatography and quantified as the oxime and methoxime derivatives using liquid partition chromatography on silicic acid. The availability of [U-14C]succinic semialdehyde permits the reliable assay of succinic semialdehyde dehydrogenase in crude cell extracts of lymphocytes isolated from human blood, cultured human lymphoblasts, and other tissues where 4-aminobutyric acid metabolism is known to occur.

Succinic semialdehyde dehydrogenase deficiency: an inborn error of gamma-aminobutyric acid metabolism

Gamma-hydroxybutyric aciduria is a disorder of gamma-aminobutyric acid metabolism in which a compound of known neuropharmacologic activity accumulates. We have studied two patients in whom high levels of gamma-hydroxybutyric acid were found in blood, urine and cerebrospinal fluid. A coupled assay has been developed which estimates succinic semialdehyde dehydrogenase activity in isolated human lymphocytes. The mean activity of succinic semialdehyde dehydrogenase in a control and the four parents and two healthy siblings of these patients was 8.8 +/- 1.9 pmol . min-1 . mg-1 protein. In the patients the activities were 0.8 and 1.1 pmol . min-1 . mg-1 protein, approximately 9-13% of control. In the presence of saturating amounts of NAD+, lymphocyte sonicates, derived from the patients accumulated a significant amount of 14C-succinic semialdehyde from 14C-gamma aminobutyric acid, whereas none could be detected in controls. The data suggest a deficiency of succinic semialdehyde dehydrogenase in these patients, the first documented defect of the metabolism of gamma-aminobutyric acid in man.

3-hydroxy-3-methylglutaric aciduria: a new assay of 3-hydroxy-3-methylglutaryl-coa lyase using high performance liquid chromatography

A new assay has been developed for 3-hydroxy-3-methylglutaryl-CoA lyase, the final enzyme in the leucine degradative pathway. The assay was performed by incubating lysates of fibroblasts with [glutaryl-3-14C](D,L)-3-hydroxy-3-methyl-glutaryl coenzyme A. The products were analysed by high performance liquid chromatography with continuous liquid scintillation counting. This provided simultaneous identification and quantification of one of the enzymatic products, [3-14C]acetoacetic acid. The mean 3-hydroxy-3-methylglutaryl-CoA lyase activity in fibroblasts from five controls was 732 +/- 81 (SD) pmol/min X mg protein. Using this assay, we have studied skin fibroblasts cultured from a patient with 3-hydroxy-3-methylglutaric aciduria and found 3% of normal 3-hydroxy-3-methylglutaryl-CoA lyase activity. The activities in skin fibroblasts cultured from the parents were 46 and 53% of control activity which is consistent with heterozygocity. Kinetic studies of 3-hydroxy-3-methylglutaryl-CoA lyase in skin fibroblasts cultured from two normal subjects yielded Km values of 14.4 and 18.8 mumol/l for 3-hydroxy-3-methylglutaryl-CoA.

Oxidation of fatty acids in cultured fibroblasts: a model system for the detection and study of defects in oxidation

A number of recently described inherited disorders interfere with the oxidation of fatty acids. In these disorders at least three different metabolic steps may be affected: (1) transport of long chain fatty acids into the mitochondria as in carnitine deficiency and carnitine palmitoyl transferase deficiency (CPT); (2) multiple acyl CoA dehydrogenase deficiency or glutaric aciduria type II (GAII) due presumably to a defective common electron transfering flavoprotein or iron sulfur flavoprotein; (3) specific long or medium chain fatty acyl CoA dehydrogenase deficiency as in inherited dicarboxylic aciduria. In order to develop a system for the detection and the study of the consequences of defects such as these on the oxidation of fatty acids, we investigated the metabolism of oleate (18 carbons), octanoate (eight carbons) and butyrate (four carbons) in intact cultured fibroblasts from patients with CPT deficiency, GAII, and dicarboxylic aciduria. In CPT deficient cells there was a markedly deficient ability to oxidize [1-14C] and [U-14C] oleate (19 and 5% of normal, respectively), whereas oxidations of [1-14C] octanoate and [1,4-14C] succinate were significantly increased (150 and 222%, respectively), and [1-14C] butyrate oxidation was normal. GAII cells displayed a nearly complete defect in the oxidation of [1-14C] and [U-14C] oleate (8 and 1%, respectively), as well as of [1-14C] octanoate and [1-14C] butyrate (8 and 5% of normal, respectively). The oxidation of [1,4-14C] succinate by GAII cells was normal. Cells from a patient with dicarboxylic aciduria showed a significant reduction in [14CO2] production from [U-14C] oleate (57%) and [1-14C] octanoate (31%) and a normal oxidation of [1-14C] oleate, [1-14C] butyrate, and [1,4-14C] succinate. These observations are consistent with available information on the normal metabolism of fatty acids in liver and muscle and also with the hypothesis about the molecular localization of the defects in GAII and inherited dicarboxylic aciduria. They demonstrate that intact cultured skin fibroblasts represent a reliable and convenient model for the investigation of fatty acid oxidation in man. Many aspects of the human acyl CoA dehydrogenases and their physiologic functions remain unknown, among them the problem of their acyl chain length specificity. Studies in cultured fibroblasts from patients with presumed mutations affecting the metabolism of fatty acids provide a means for the elucidation of these defects and at the same time give information on normal metabolic functions. It appears likely that a number of previously unrecognized defects in this area of metabolism remain to be found. The availability of a model system for their study in cultured fibroblasts should facilitate their discovery.