G. K. Brown

Urinary organic acids in succinic semialdehyde dehydrogenase deficiency: Evidence of α-oxidation of 4-hydroxybutyric acid, interaction of succinic semialdehyde with pyruvate dehydrogenase and possible secondary inhibition of mitochondrial β-oxidation

SummaryIn addition to the previously reported abnormalities, urine extracts from three cases of succinic semialdehyde dehydrogenase deficiency have shown consistently increased amounts of 2,4-dihydroxybutric acid, and its lactone, and 3-hydroxypropionic acid, metabolites related to the α-oxidation of 4-hydroxybutyric acid.Threo- anderythro-4,5-dihydroxyhexanoic acids have also been identified for the first time and probably arise from the reaction of succinic semialdehyde with an intermediate in the pyruvate dehydrogenase pathway. Adipic acid excretion is also consistently raised, suggesting secondary interference with mitochondrial β-oxidation. The presence of these metabolites could be a source of diagnostic confusion.

Malonyl coenzyme a decarboxylase deficiency

A patient is described with a deficiency of the mitochondrial enzyme, malonyl CoA decarboxylase — an inborn error of metabolism not recognized previously. The enzyme defect was first suspected because of persistent excretion of malonic and methylmalonic acids in urine in a child with repeated episodes of vomiting, some requiring hospitalization. Disturbances of lipid metabolism were demonstrated.

Malonyl coenzyme A decarboxylase deficiency. Clinical and biochemical findings in a second child with a more severe enzyme defect

A second child with a more severe deficiency of malonyl CoA decarboxylase is described. He is mildly mentally retarded and presented with vomiting, a seizure, hypoglycaemia and mild metabolic acidosis during a urinary tract infection. The urine contained increased, amounts of malonic, methylmalonic, succinic, adipic, glutaric and suberic acids. Mitochondrial malonyl CoA decarboxylase activity in cultured fibrobast extracts was 4% of the mean control value. A high fat, low carbohydrate diet led to symptomatic hypyglycaemia, a moderate metabolic acidosis and excretion in the urine of large amounts of the same organic acids and 3-hydroxybutyrate. Only relatively small quantities of malonic, methylmalonic and succinic acid were excreted in the urine when the boy was fed an isocaloric low fat, high carbohydrate diet. Acute fat and lysine loads led to increased excretion of malonic acid in the urine without affecting the excretion of the other organic acids.Experience with this patient, suggests that malonyl CoA decarboxylase serves an important function in the mitochondrion by preventing accumulation of malonyl CoA. The importance of the enzyme is best seen when fat is the main metabolic fuel. The mechanisms by which malonyl CoA produces its complex metabolic effects remain to be elucidated.

Severe illness caused by the products of bacterial metabolism in a child with a short gut

An 8-year-old boy with a short gut had six episodes of metabolic acidosis and neurological dysfunction over a 1 month period. The neurological features consisted of a depressed conscious state, confusion, aggressive behaviour, slurred speech and ataxia. The organic acid profile of urine demonstrated increased amounts of lactic, 3-hydroxypropionic, 3-hydroxyisobutyric, 2-hydroxyisocaproic, phenyllactic, 4-hydroxyphenylacetic and 4-hydroxyphenyllactic acids. Of the lactic acid 99% was d-lactic acid. The anaerobic gut flora consisted almost entirely of Lactobacilli in unusually large numbers. A course of vancomycin prevented further episodes. A urinary organic acid profile may be diagnostic when a person with a short gut develops metabolic acidosis or an unusual encephalopathy and bacterial metabolites should be considered in other patients with unusual combinations of organic acids in the urine.

Cytochrome c oxidase deficiency in subacute necrotizing encephalopathy (Leigh syndrome)

SummaryTissues and cultured fibroblasts from two patients with Leigh syndrome (subacute necrotizing encephalopathy) were examined. A systemic defect in cytochrome oxidase was identified by enzyme assay and estimation of cytochrome concentrations. Immunochemical analysis showed a reduction of most subunits of the cytochrome oxidase complex.The rate of synthesis of cytochrome oxidase subunits, determined by labelling experiments in cultured fibroblasts, was the same in the patients and normal controls. The reduced cytochrome oxidase content of the patients tissues must therefore result from abnormal turnover of the protein subunits.

Succinic semialdehyde dehydrogenase deficiency—A further case

McKusick, V. A. and Neufeld, E. F. The mucopolysaccharide storage diseases. In Stanbury, J. B., Wyngaarden, J. B., Frederickson, D. S., Goldstein, J. L. and Brown, M. S. (eds.) The Metabolic Basis of Inherited Disease, McGraw-Hill, New York, 1983, pp. 751-777 MueUer, O. T., Honey, N. K., Little, L. E., Miller, A. L. and Shows, T. B. Mucolipidosis II and III. The genetic relationships between two disorders of lysosomal enzyme biosynthesis. J. Ciin. lnvest. 72 (1983) 1016-1023 Pollard, A. C., Carey, W. F., Nelson, P. V., Poulos, A. and Hill, G. N. Enzymotogical diagnosis of a group of lysosomal storage diseases. Review of a 5-year experience with 1600 patient sample referrals. Med. J. Al~st. 2 (1980) 549-553 Poulos, A. and Beckman, K. The bile salt activation of leucocyte sphingolipid hydrolase activity and the modifying effects of Triton X-100. CIin. Chim. Acta 107 (1980) 27-35 Poulos, A. and Pollard, A. C. A rapid method for the estimation of [3-galactocerebrosidase, 13-glucocerebrosidase and sphingomyelinase activities in leucocytes. Clin. Chim. Aeta 72 (1976) 327--335 Wiebel, F. and Baserga, R. Early alteration in amino acid pools and protein synthesis of diploid fibroblasts stimulated to synthesise DNA by addition of serum. J. Cell. Physiol. 74 (1969) 191-202

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.

A carbamylphosphate synthetase deficiency with no detectable immunoreactive enzyme and no translatablemRNA

A lethal carbamylphosphate synthetase (CPS: EC 6.3.4.16) deficiency (McKusick 23730) was found in a newborn girl; who presented on the second day of life with acute hyperammonaemia, hypotonia, seizures and who died in a coma 6 days after birth. The activity of the mitochondrial urea cycle enzymes, CPS and ornithine transcarbamylase (OTC: EC 2.1.3.3) were measured on a needle biopsy sample taken from liver and showed that CPS was 1.4% of the normal mean (0.09 nmol/min/mg protein) whereas OTC activity was normal (110 nmol/min/mg protein). Immunological analysis of the liver sample showed no detectable immunoreactive CPS and confirmed the presence of normal levels of OTC. RNA was extracted from postmortem liver andin vitro translation experiments showed that there was no translatable CPSmRNA and confirmed that no CPS protein was synthesized in this child. The absence of translatablemRNA is explicable in terms of a genetic defect which results in a failure to synthesizemRNA for CPS, or synthesis of a defective form ofmRNA which is not translated.

“Cerebral” lactic acidosis and cerebrospinal fluid pH

Sir: Our intention was to stress the puzzling fact that, firstly, the 13-gene is apparently derepressed earlier in fetal life than the 5-gene, although being situated downstream of the latter on the non-a-globin cluster, and, secondly, ~-globin synthesis, once started in connection with the switch, makes up for its relative amount compared to 13-globin. It is certainly a good idea of Dr. Ozsoylu to look at the mechanism of translation for an explanation. As far as we understand his suggestion, however, it may explain the second point but not the first i.e. the production of Hb A during fetal life without production of Hb A2.

Deoxyribose-5-phosphate aldolase deficiency―a harmless inborn error of metabolism

Evidence is presented that a deficiency of 2-deoxyribose-5-phosphate aldolase was present in a previously described patient who excreted metabolites of 2-deoxyribose in his urine. Minor clinical abnormalities present did not appear related to this disorder.