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Deficient acetyl CoA carboxylase activity in multiple carboxylase deficiency.

Multiple carboxylase deficiency has previously been characterized by deficient activity of three biotin-dependent enzymes: propionyl CoA carboxylase, pyruvate carboxylase and beta-methylcrotonyl CoA carboxylase. We have demonstrated that the activity of a fourth carboxylase, acetyl CoA carboxylase (ACC), is also deficient in fibroblasts from two patients with this disorder. Furthermore, ACC activity increased six- to eight-fold when cells from these patients were incubated in culture medium containing supplemental biotin. If the primary defect in multiple carboxylase deficiency is due to deficient activity of holocarboxylase synthetase, our results would indicate that there may be a common holocarboxylase synthetase, or at least a common subunit, for all the carboxylases. Finally, since ACC catalyzes the initial step in fatty acid biosynthesis, our results further suggest the importance of dietary supplementation with fatty acids in addition to treating these patients with pharmacologic doses of biotin.

Acetyl-CoA Carboxylase

Multiple carboxylase deficiency.

1. The multiple carboxylase deficiencies are inborn errors in the metabolism of biotin in which there is defective activity of propionyl CoA carboxylase, 3-methylcrotonyl CoA carboxylase and pyruvate carboxylase. 2. Two distinct disorders have been described. 3. In one the fundamental defect is in the enzyme holocarboxylase synthetase which catalyzes the molecular activation of the apocarboxylase proteins. 4. In the other the fundamental defect is in biotinidase which catalyzes the reutilization of biotin and may be involved in its digestion and intestinal absorption.

Amidohydrolases

Prenatal administration of biotin in biotin responsive multiple carboxylase deficiency.

Biotin responsive multiple carboxylase deficiency was suspected in a third trimester conceptus on the basis of enzymatic confirmation in fibroblasts cultured from an earlier sibling who suffered a demise in the immediate neonatal period. Maternal urinary organic acid profile was normal throughout the final 4 wk of pregnancy. Oral administration of biotin, 10 mg/day to the mother resulted in a 100-fold increase in urinary biotin excretion within 7 days. Urinary biotin excretion over the subsequent 2 wk decreased steadily, suggesting either decreased maternal absorption or increased fetal sequestration. After the birth of nonidentical twins, cord blood and urinary organic acid profiles of the infants were normal. However, cord blood biotin concentration was 4 to 7-fold that of normal newborns. Subsequent enzymatic and genetic complementation studies utilizing cultured skin fibroblasts from the infants demonstrated one of them to be affected by the multiple carboxylase defect, although he was clinically and biochemically normal throughout the neonatal period. Thus, prenatal therapy of this inborn enzymatic defect can be safely and effectively accomplished by administration of pharmacologic biotin doses in the last month of pregnancy.

Biotin

Biotinidase deficiency: the enzymatic defect in late-onset multiple carboxylase deficiency.

Late-onset multiple carboxylase deficiency is characterized clinically by skin rash, alopecia, seizures and ataxia and occasionally by candidiasis and developmental delay. Biochemically, these individuals exhibit findings consistent with a combined deficiency of the biotin-dependent carboxylases. We have found that the activity of the enzyme biotinidase is also deficient in the sera of five affected children (0 to 3% of mean control activity, 5.80 +/- 0.89 nmol X min-1 X ml-1 serum), and believe that it represents the primary biochemical defect in this disease. Biotinidase catalyzes the removal of biotin from the epsilon-amino group of lysine, through which biotin is covalently bound to the four known human carboxylases, thereby regenerating biotin for reutilization. The deficient activity in our patients was not due to an inhibitor, particularly biotin. It is also not a consequence of feedback control in affected individuals under treatment with pharmacologic doses of biotin. The biotinidase activities of the parents of those children who were available for study were intermediate between deficient and normal values (46% to 65% of mean normal activity). Children lacking biotinidase activity are unable to recycle biotin, and are thus entirely dependent upon exogenous biotin to prevent deficiency. Our findings indicate that the primary biochemical defect in late-onset multiple carboxylase deficiency is in biotinidase activity which is inherited as an autosomal recessive trait.

Amidohydrolases

Mutant holocarboxylase synthetase: evidence for the enzyme defect in early infantile biotin-responsive multiple carboxylase deficiency.

Biotin-responsive multiple carboxylase deficiency is an inherited disorder of organic acid metabolism in man in which there are deficiencies of propionyl-coenzyme A (CoA), 3-methylcrotonyl-CoA, and pyruvate carboxylases that can be corrected with large doses of biotin. It has been proposed that the basic defect in patients with the early infantile form of the disease is in holocarboxylase synthetase, the enzyme that covalently attaches biotin to the inactive apocarboxylases to form active holocarboxylases. We have developed an assay for holocarboxylase synthetase in extracts of human fibroblasts using as substrate apopropionyl-CoA carboxylase partially purified from livers of biotin-deficient rats. Fibroblasts from the initial patient with the infantile form of biotin-responsive multiple carboxylase deficiency were shown to have abnormal holocarboxylase synthetase activity with a maximum velocity about 30-40% of normal, a Km for ATP of 0.3 mM similar to the normal Km of 0.2 mM, and a highly elevated Km for biotin of 126 ng/ml, about 60 times the normal Km of 2 ng/ml. These results show that the primary defect in this patient is a mutation affecting holocarboxylase synthetase activity, and thus a genetic defect of the metabolism of biotin.

Amino Acid Metabolism, Inborn Errors

Biochemical evidence for diverse etiologies in biotin-responsive multiple carboxylase deficiency.

Biotin-responsive multiple carboxylase deficiency can be categorized by clinical criteria into a neonatal-onset disorder and distinct syndrome of infantile onset. Pedigrees in each instance are consistent with autosomal recessive inheritance. For a neonatal-onset proband, the sensitivity to relative biotin deprivation and the rapid clinical response to biotin supplementation are reflected by in vitro studies. Specific activities of biotin-dependent pyruvate carboxylase, propionyl CoA carboxylase, and 1-methylcrotonyl CoA carboxylase are 0.8 to 16% of mean control values after growth of fibroblasts in intermediate and very low biotin concentrations. Following relative biotin depletion, pyruvate carboxylase activity returns to normal after only 14 hr of growth in biotin-supplemented medium. In contrast, carboxylase activities in fibroblasts of an infantile-onset proband remain normal at very low biotin concentrations, even when avidin is added to the growth medium. The clinical heterogeneity, taken together with the distinct responses of cultured skin fibroblasts to biotin deprivation in vitro, probably reflect fundamentally different etiologies for the two categories of biotin-responsive multiple carboxylase deficiency.

Adult

Acetyl CoA carboxylase in cultured fibroblasts: differential biotin dependence in the two types of biotin-responsive multiple carboxylase deficiency.

In biotin-responsive multiple carboxylase deficiency, a characteristic organic aciduria reflects in vivo deficiency of mitochondrial propionyl CoA carboxylase, 3-methylcrotonyl CoA carboxylase, and pyruvate carboxylase. A possible primary or secondary defect in biotin absorption leads to an infantile-onset syndrome, while abnormal holocarboxylase synthetase activity has been identified in the neonatal-onset form. While distinct mitochondrial and cytosolic holocarboxylase synthetase biotinylation systems may exist in avian tissues, the system has not been characterized in humans. Toward this objective, we studied the biotin dependence of a cytosolic carboxylase, acetyl CoA carboxylase (ACC), in cultured skin fibroblasts of both types of multiple carboxylase deficiency. ACC specific activities in control and infantile-onset cells were not distinguishable at all biotin concentrations: with decreasing biotin availability (+ avidin), there were only modest decrements in ACC activity in both these cell types. In contrast, there were pronounced declines of ACC activity in neonatal-onset (holocarboxylase synthetase-deficient) cells after growth in low biotin concentrations, and activity was undetectable in + avidin. ACC activity was rapidly restored with biotin repletion to biotin-starved holocarboxylase synthetase-deficient cells, and this restoration was largely independent of protein synthesis. The behavior of the cytosolic carboxylase, ACC, is in all these respects identical to that of the mitochondrial carboxylases, an observation consistent with the existence of similar biotinylation mechanisms in the two cell compartments. Further, the data support the notion that at least some components of the holocarboxylase synthetase system are shared by mitochondria and cytosol in humans, and are consistent with the suggestion that restoration of activity in biotin-depleted cells represents biotinylation of preexisting enzyme protein. The modest decrements in ACC activity in normal and infantile-onset cells may be related to the compromised epidermal integrity observed in that form of multiple carboxylase deficiency. Finally, ACC and mitochondrial carboxylase activities were compared in cells from mutants representing a spectrum of clinical severity. Cells from later-onset patients of intermediate clinical severity were ultimately classifiable as putative holocarboxylase synthetase-deficient cells on chemical criteria. Accurate etiologic classification cannot be based on clinical presentation alone, and biochemical studies should be performed on all patients. Accordingly, we propose a classification of multiple carboxylase deficiency based on biochemical criteria.

Acetyl-CoA Carboxylase

Two forms of biotin-responsive multiple carboxylase deficiency.

Biotin-responsive multiple carboxylase deficiencies are classified into early and late forms. The early form showed higher urinary excretion of 3-hydroxyisovalerate and 3-hydroxypropionate than the late form and was associated with normal plasma biotin concentrations. It is proposed that holocarboxylase synthetase and intestinal biotin absorption are defective in the early and late forms respectively.

Acute Disease

[Alopecia, chronic candidodis, mental retardation and repeated ketoacidosic comas curable by biotin administration: multiple carboxylases deficiency (author's transl)].

Multiple carboxylases deficiency, a recently identified metabolic disease in infants, can be cured by the administration of biotine, a cofactor of the carboxylases: pyruvate, propionyl coenzyme A (CoA), methylcrotonyl CoA, and acetyl CoA. The disorder presents as alopecia, associated with chronic candidosis, psychomotor retardation, and frequent episodes of ketoacidosis coma which responded to biotine treatment. Biological signs, related to the deficiency of the individual enzymes, are observed as hyperlactacidemia, propionic aciduria, and methylcrotonylglycinuria. The metabolic basis of this vitamin-dependent size is still obscure, but the research stimulated by this new disease should clarify the still poorly understood physiological role of this vitamin in humans.

Acidosis

Multiple carboxylase deficiency: clinical and biochemical improvement following neonatal biotin treatment.

Multiple carboxylase deficiency is characterized by deficient activities of three biotin-dependent enzymes, propionyl coenzyme A carboxylase, pyruvate carboxylase, and beta-methylcrotonyl coenzyme A carboxylase. A newborn infant was seen with metabolic ketoacidosis, hyperammonemia, organic aciduria, seizures, and coma. Multiple carboxylase deficiency was subsequently confirmed by enzyme activity determinations in his peripheral blood leukocytes and cultured skin fibroblasts. The infant's neurologic and metabolic status improved markedly within a few days of administration of pharmacologic doses of oral biotin. His EEG, which was distinctly abnormal, became normal; his extensive computed tomography scan changes resolved, with the exception of ventricular dilation, over the next two months. After two weeks of biotin treatment the excretion of abnormal organic acid metabolites was reduced and his carboxylase activities increased to the normal range. However, the activities of these enzymes increased only to 30% to 55% of normal in fibroblasts incubated in supplemental biotin. This partial correction of enzyme activity differs from that observed in other individuals with multiple carboxylase deficiency and suggests biochemical heterogeneity in this disorder. Prompt diagnosis and intervention can avert some of the pathologic complications of this biotin-responsive condition.

Biotin

Fatty acid transport in multiple carboxylase deficiency fibroblasts.

Holocarboxylase synthetase (HS) and biotinidase deficiencies have been identified as causes of biotin-responsive multiple carboxylase deficiency. Acetyl-CoA carboxylase (ACC) deficiency has been shown to occur in multiple carboxylase deficiency, and HS(-) fibroblasts are being employed to investigate compensatory regulatory responses in cells deficient in ACC. In previous studies, biotin starved HS(-) fibroblasts showed a reduced fatty acid content, an abnormal percentage composition of fatty acids, and a preservation of longer-chain fatty acid contents of cells. We herein ask whether the mutant cells show compensatory increases in the transport of longer-chain fatty acids from the medium into fibroblasts. In the present experiments there was no change in the uptake of arachidonate, palmitate or oleate following growth of mutant and control fibroblasts in (+) or (-) biotin conditions. Differential fatty acid uptake from the medium is therefore not a compensatory mechanism in HS(-) cells, and cannot account for the specific changes in fatty acid composition produced by biotin restriction.

Arachidonic Acid

Abnormal fatty acid composition of biotin-responsive multiple carboxylase deficiency fibroblasts.

Clinical and biochemical correlations in the biotin-responsive multiple carboxylase deficiencies have suggested that disordered lipogenesis plays a role in the pathogenesis of the disease. In particular, the activity of biotin-dependent acetyl CoA carboxylase and the de novo synthesis of fatty acids are reduced in mutant fibroblasts. In the present work, we examine the biochemical consequences of these deficiencies, and document and characterize an abnormal fatty acid composition in holocarboxylase synthetase deficiency fibroblasts. Following growth in biotin-restricted medium, the total fatty acid content of mutant cells is reduced. There were significant reductions in the percentage as 16:0, 18:0 and 20:3N9 fatty acids, with the proportion of longer-chain fatty acids either increased or maintained at control levels. The cellular content of 16:0, 16:1, 18:0, 18:1 and 20:3N9 fatty acids was reduced, while that of the longer-chain fatty acids was preserved at control levels in mutant cells deprived of biotin. We speculate that the components of the altered fatty acid pools may be disproportionately incorporated into complex lipids in mutant cells, with pathologic effects on the multiple carboxylase deficiency phenotype.

Biotin

Lactic acidosis in biotin-responsive multiple carboxylase deficiency caused by holocarboxylase synthetase deficiency of early and late onset.

Two patients with biotin-responsive multiple carboxylase deficiency, both presenting with predominant lactic acidosis, are reported. One with disease of early neonatal onset had considerable acute neurologic and persistent dermatologic abnormalities. The other, with late juvenile-onset disease, had chronic neurologic abnormalities without dermatologic findings. Early-onset cases generally have been associated with holocarboxylase synthetase deficiency, whereas those of juvenile onset have been characterized as representing defects in intestinal biotin absorption. However, enzyme analyses of fibroblasts from both patients, grown in biotin-deficient medium, revealed markedly diminished activities of pyruvate, propionyl-CoA, and beta-methylcrotonyl-CoA carboxylases, and all three enzymes showed normal activities after growth in biotin-rich medium. Furthermore, lymphoblast enzyme analysis in the patient with disease of early onset had previously revealed a defect in holocarboxylase synthetase, and fibroblast complementation studies showed that both patients belong to the bio complementation group. These findings indicate that considerable clinical heterogeneity exists among patients with holocarboxylase synthetase deficiency, an observation which does not permit differentiation of the biochemical forms of multiple carboxylase deficiency on the basis of age at onset and clinical presentation.

Acidosis

Alopecia and periorificial dermatitis in biotin-responsive multiple carboxylase deficiency.

Three siblings with infantile-onset biotin-responsive multiple carboxylase deficiency are described. Recognition of the characteristic dermatologic manifestations, alopecia and periorificial dermatitis, should result in early diagnosis and institution of potentially lifesaving therapy with biotin. Other metabolic disorders may present a similar clinical picture. Immunologic dysfunction and/or aberration in lipid or branched chain amino acid metabolism may be the common pathophysiologic link in some or all of these disorders.

Alopecia

Evidence for a defect of holocarboxylase synthetase activity in cultured lymphoblasts from a patient with biotin-responsive multiple carboxylase deficiency.

We report here the expression of biotin-responsive multiple carboxylase deficiency in cultured lymphoblasts of a patient whose fibroblasts belong to the bio genetic complementation group. Cultured lymphoblasts from the patient lost propionyl-CoA carboxylase (PCC) and beta-methylcrotonyl-CoA carboxylase (MCC) activities at a faster rate than normal cells when grown in biotin-deficient medium. Recovery of normal PCC and MCC activities, which was independent of protein synthesis, required a 2,500-fold higher biotin concentration than that required by normal lymphoblasts. Holocarboxylase synthetase activity was detected in cell-free extracts through the biotinylation of endogenous apo-PCC in the presence of ATP to form active holo-PCC. While the apo-PCC in extracts of normal biotin-starved lymphoblasts could be activated to 28% of maximal activity, extracts of patient lymphoblasts did not exhibit any ATP and biotin-dependent increase in PCC activity. A normal cell extract, cleared of apocarboxylases by immunoprecipitation, stimulated the PCC activity of a patient cell extract 20-fold. These results indicate that the apoenzyme in bio cells is normal and that the defect lies in the holocarboxylase synthetase.

Biotin

Biotin-responsive multiple carboxylase deficiency in an 8-year-old boy with normal serum biotinidase and fibroblast holocarboxylase-synthetase activities.

An 8-year-old boy with late onset multiple carboxylase deficiency is described. Biotinidase deficiency and holocarboxylase-synthetase deficiency have been excluded. A very slow biochemical response to biotin was found. The decrease in urinary organic acid excretion followed first-order kinetics with a half-life of about 50 days. The initially low carboxylase activities in thrombocytes were increased but not normalized after 3 months of treatment.

Amidohydrolases