[Biotinidase deficiency. Its form of presentation and response to treatment].
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Acyltransferases↗
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Mutations causing profound biotinidase deficiency in children ascertained by newborn screening in the United States occur at different frequencies than in symptomatic children.
Biotinidase deficiency is an autosomal recessive disorder of biotin metabolism that can lead to varying degrees of neurologic and cutaneous symptoms when untreated. Because this disorder meets the criteria for newborn screening, many states and countries perform this testing. Because newborn screening should result in complete ascertainment of mutations causing profound biotinidase deficiency (less than 10% of mean normal serum activity), we compared the mutations in a group of 59 children with profound biotinidase deficiency who were identified by newborn screening in the United States with 33 children ascertained by exhibiting symptoms. Of the 40 total mutations identified among the two populations, four mutations comprise 59% of the disease alleles studied. Two of these mutations occur in both populations, but in the symptomatic group at a significantly greater frequency. The other two common mutations occur only in the newborn screening group. Because two common mutations do not occur in the symptomatic population, it is possible that individuals with these mutations either develop mild or no symptoms if left untreated. However, inasmuch as biotin treatment is inexpensive and innocuous, it is still recommended that all children with profound biotinidase deficiency be treated.
Amidohydrolases↗
Molecular analysis of new Japanese patients with holocarboxylase synthetase deficiency.
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Biotin↗
Biotin in metabolism and its relationship to human disease.
Biotin, a water-soluble vitamin, is used as cofactor of enzymes involved in carboxylation reactions. In humans, there are five biotin-dependent carboxylases: propionyl-CoA carboxylase; methylcrotonyl-CoA carboxylase; pyruvate carboxylase, and two forms of acetyl-CoA carboxylase. These enzymes catalyze key reactions in gluconeogenesis, fatty acid metabolism, and amino acid catabolism; thus, biotin plays an essential role in maintaining metabolic homeostasis. In recent years, biotin has been associated with several diseases in humans. Some are related to enzyme deficiencies involved in biotin metabolism. However, not all biotin-responsive disorders can be explained based on the classical role of the vitamin in cell metabolism. Several groups have suggested that biotin may be involved in regulating transcription or protein expression of different proteins. Biotinylation of histones and triggering of transduction signaling cascades have been suggested as underlying mechanisms behind these non-classical biotin-deficiency manifestation in humans.
Amino Acid Sequence↗
[Biotinidase deficiency. Results of neonatal screening 1985-1989 in Lower Saxony].
During a five-year-period (1985-1989) 420,000 newborns in Lower Saxony, FRG, were screened for biotinidase deficiency using biotinyl-para-amino-benzoic-acid as substrate. Three newborns with profound biotinidase deficiency (activity 1.1%, 2.1%, 2.3% of mean normal activity level) were detected. Nine newborns had partial biotinidase deficiency (activity 17-26% of mean normal activity level), thus giving an incidence of 1:140,000 with profound, and 1:46,667 with partial biotinidase deficiency, respectively. The infants with profound biotinidase deficiency are treated with biotin (2 x 5 mg/day) from the 3rd, 6th and 8th week of life and have developed normally so far. The children with partial biotinidase deficiency are not treated but followed up closely. The necessity of newborn screening for biotinidase deficiency is stressed.
Amidohydrolases↗
Resolution of subependymal cysts in neonatal holocarboxylase synthetase deficiency.
Holocarboxylase synthetase deficiency is typically a biotin responsive disorder that presents with lactic acidosis, tachypnea, temperature instability, and shock in neonates (Briones et al.1989 and Fuchshuber et al. 1992). The primary defect in cases studied to date appears to be the decreased affinity of HCS for its substrate, biotin (Gompertz et al. 1971). Supplemental biotin can provide sufficient substrate to increase HCS enzymatic function and thereby permit biotinylation of the four carboxylase apoenzymes (Briones et al. 1989). We report an infant with HCS deficiency who presented with lactic acidosis, shock, and hypertonia. Subependymal cysts were identified on cranial ultrasound and subsequently confirmed by MRI. Six months following biotin supplementation, she is developmentally normal and MRI of the brain shows complete resolution of the cysts.
Biotin↗
Biotinidase deficiency: early neurological presentation.
Three patients with biotinidase deficiency are described. Two presented at eight weeks of age with anticonvulsant-resistant fits, developmental delay and hypotonia. Treatment has been effective. The third developed ataxia and alopecia at 14 months and died suddenly at 19 months of age. In all three cases the diagnosis was not considered quickly enough. Biotinidase deficiency is a treatable cause of severe neurological problems.
Acidosis, Lactic↗
Congenital deficiency of vitamin K-dependent coagulation factors associated with central nervous system anomalies.
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Arnold-Chiari Malformation↗
Inborn errors of biotin metabolism.
The important role of biotin in human physiology has been highlighted by the recognition of two newly discovered human inborn errors of the metabolism of biotin. The molecular defect in the neonatal-onset disease is in the enzyme holocarboxylase synthetase. The defect in the later infantile-onset disease is in the enzyme biotinidase. Both disorders present with impressive clinical manifestations involving the skin and hair. In the neonatal disease, alopecia totalis is associated with a bright red scaly total body eruption. In biotinidase deficiency, the alopecia is more patchy and the skin lesions resemble acrodermatitis enteropathica. Both disorders are complicated by recurrent episodes of life-threatening acidosis and massive ketosis.
Amidohydrolases↗
Biotinidase deficiency: result of treatment with biotin from age 12 years.
A boy with severe symptoms of biotinidase deficiency diagnosed at the age of 12 years showed a remarkable improvement of his neurological picture and normalization of brain magnetic resonance imaging abnormalities when prescribed oral biotin.
Amidohydrolases↗
Neonatal screening for biotinidase deficiency in north eastern Italy.
Biotinidase deficiency satisfies all the criteria for incorporation into neonatal mass screening programmes for inborn errors of metabolism. We report our preliminary experiences with screening of 24,300 newborns during a 6 month-period when 1 infant with biotinidase deficiency was detected. On the basis of these results, this disorder appears to be as common as other well known metabolic disorders for which mass screening is available.
Amidohydrolases↗
[Importance of biotin metabolism].
Biotin is a water soluble enzyme cofactor that belongs to the vitamin B complex. In humans, biotin is involved in important metabolic pathways such as gluconeogenesis, fatty acid synthesis, and amino acid catabolism by acting a as prosthetic group for pyruvate carboxylase, propionyl-CoA carboxylase, beta-methylcrotinyl-CoA carboxylase, and acetyl-CoA carboxylase. Carboxylases are synthesized as apo-carboxylases without biotin and the active form is produced by their covalent binding of biotin to the epsilon-amino group of a lysine residue of the apocarboxylases. This reaction is catalyzed by the holo-carboxylase synthetase. The last step in the degradation of carboxylases, the cleavage of the biotinyl moiety from the epsilon-amino group lysine residues, is catalyzed by biotinidase and results in the release of free biotin, which can be recycled. Biotin regulates the catabolic enzyme propionyl-CoA carboxylase at the posttranscriptional level whereas the holo-carboxylase synthetase is regulated at the transcriptional level. Aside from its role in the regulation of gene expression of carboxylases, biotin has been implicated in the induction of the receptor for the asialoglycoprotein, glycolytic enzymes and of egg yolk biotin binding proteins. Biotin deficiency in humans is extremely rare and is generally associated with prolonged parenteral nutrition, the consumption of large quantities of avidin, usually in the form of raw eggs, severe malnutrition and, inherited metabolic disorders. In humans, there are autosomal recessive disorders of biotin metabolism that result from the disruption of the activity of biotinidase or holo-carboxylase synthetase.
Adenosine Triphosphate↗
[Biotinidase deficiency: a congenital metabolic disease which can be successfully treatment with vitamin H].
At the age of 13 months a patient developed muscular hypotonia, deafness of the inner ear and cutaneous symptoms (alopecia; skin rash, complicated by superinfection with monilia). Biochemical assays revealed compensated metabolic acidosis, pathologically high lactate and pyruvate concentrations in the blood and cerebro-spinal fluid, as well as increased urinary excretion of 3-OH-isovaleric acid, 3-methylcrotonylglycine and lactate. The patient was diagnosed as suffering from autosomal recessive biotinidase deficiency on the basis of severely reduced biotinidase activity in plasma (0.05 nmol/min/ml). In both his parents and brother heterozygosity was found. Institution of therapy with a daily dose of 10 mg biotin rapidly removed most of the symptoms; after six months of treatment the deafness had improved significantly.
Acid-Base Equilibrium↗
Profound biotinidase deficiency caused by a point mutation that creates a downstream cryptic 3' splice acceptor site within an exon of the human biotinidase gene.
Biotinidase recycles the vitamin biotin from biocytin upon the degradation of the biotin-dependent carboxylases. We have identified a novel point mutation within the biotinidase gene that encodes the signal peptide in two unrelated individuals with profound biotinidase deficiency. Sequence analysis of genomic DNA from these individuals revealed a G to A transition (G100-->A) located 57 bases downstream of the authentic splice acceptor site in exon B. Although this mutation predicts a G34S substitution, it also generates a 3' splice acceptor site. Sequence of the PCR-amplified cDNA from the homozygous child revealed that all the product was shorter than that of normal individuals and was the result of aberrant splicing. The aberrantly spliced transcript lacked 57 bases, including a second in-frame ATG, that encode most of the putative signal peptide and results in an in-frame deletion of 19 amino acids. The mutation results in failure to secrete the aberrant protein into the blood. This is the first reported example in which a point mutation creates a cryptic 3' splice acceptor site motif that is used preferentially over the upstream authentic splice site. The preferential usage of the downstream splice site is not consistent with the 5'-3' scanning model, but is consistent with the exon definition model of RNA splicing.
Amidohydrolases↗
Bioavailability of biotin given orally to humans in pharmacologic doses.
BACKGROUND: Patients with carboxylase deficiency are treated with pharmacologic doses of biotin. OBJECTIVE: We sought to determine the bioavailability of biotin at pharmacologic doses. DESIGN: Biotin was administered orally (2.1, 8.2, or 81.9 micromol) or intravenously (18.4 micromol) to 6 healthy adults in a crossover design with > or =2 wk between each biotin administration. Before and after each administration, timed 24-h urine samples were collected. Urinary biotin and biotin metabolites were analyzed by an HPLC avidin-binding assay. RESULTS: Urinary recoveries of biotin plus metabolites were similar (approximately 50%) after the 2 largest oral doses and the 1 intravenous dose, suggesting 100% bioavailability of the 2 largest oral doses. For unexplained reasons, the apparent recovery of the smallest oral dose was about twice that of the other doses. For all 4 doses, biotin accounted for >50% of the total of biotin and biotin metabolites in urine. Bisnorbiotin (13-23%), biotin-d,l-sulfoxide (5-13%), bisnorbiotin methyl ketone (3-9%), and biotin sulfone (1-3%) accounted for the remainder. The percentage excretion of biotin was greater when biotin was administered intravenously and for the largest oral dose than for the 2 smallest oral doses. CONCLUSION: Our data provide evidence that oral biotin is completely absorbed even when pharmacologic doses are administered. Biotin metabolites account for a substantial portion of total urinary excretion and must be considered in bioavailability studies. We speculate that renal losses of biotin (as a percentage of the dose administered) are moderately elevated when pharmacologic doses of biotin are administered.
Administration, Oral↗
New insight into the causes of immunodeficiency disorders.
The ability to define subpopulations of immunologically competent lymphocytes has permitted an enhanced understanding of the interaction between functionally distinct components of the immune system. T cells can provide help in antibody formation or they may suppress antibody production. Abnormal immunoregulatory mechanisms have been demonstrated in the hyperimmunoglobulin E-recurrent infection syndrome. This disorder is associated with a marked elevation of IgE and specific elevations of IgE antibodies directed toward staphylococcal antigens. Abnormal T cell regulation of immune responses has been demonstrated. Graft-versus-host disease (GVHD) occurs in an immunodeficient patient who has received an infusion of immunocompetent cells. The diagnosis of graft-versus-host (GVH) reaction may be complicated by the protean manifestations of the disorder. The acute form, consisting of a maculopapular rash, fever, and diarrhea, may be confused with acute infection or drug reaction. Chronic GVHD has been incorrectly diagnosed as histiocytosis X, acrodermatitis enteropathica, or scleroderma. Utilizing chromosome markers and/or identification of histocompatibility antigens, the presence of circulating lymphocytes from donor immunocompetent cells (blood transfusion, maternal source) can be documented. The development of sensitive technics for identifying cells can establish a precise diagnosis. Certain immunodeficiency disorders can be identified by biochemical means. Biotin-dependent multiple carboxylase enzyme deficiency is associated with a chronic dermatitis, alopecia, ataxia, and secondary infection of the skin with Candida. The disorder responds promptly to the administration of biotin with correction of dermatologic, neurologic, and immunologic abnormalities.
Animals↗
Structure of the biotinyl domain of acetyl-coenzyme A carboxylase determined by MAD phasing.
BACKGROUND: Acetyl-coenzyme A carboxylase catalyzes the first committed step of fatty acid biosynthesis. Universally, this reaction involves three functional components all related to a carboxybiotinyl intermediate. A biotinyl domain shuttles its covalently attached biotin prosthetic group between the active sites of a biotin carboxylase and a carboxyl transferase. In Escherichia coli, the three components reside in separate subunits: a biotinyl domain is the functional portion of one of these, biotin carboxy carrier protein (BCCP). RESULTS: We have expressed natural and selenomethionyl (Se-met) BCCP from E. coli as biotinylated recombinant proteins, proteolyzed them with subtilisin Carlsberg to produce the biotinyl domains BCCP and Se-met BCCPsc, determined the crystal structure of Se-met BCCPsc using a modified version of the multiwavelength anomalous diffraction (MAD) phasing protocol, and refined the structure for the natural BCCPsc at 1.8 A resolution. The structure may be described as a capped beta sandwich with quasi-dyad symmetry. Each half contains a characteristic hammerhead motif. The biotinylated lysin is located at a hairpin beta turn which connects the two symmetric halves of the molecule, and its biotinyl group interacts with a non-symmetric protrusion from the core. CONCLUSIONS: This first crystal structure of a biotinyl domain helps to unravel the central role of such domains in reactions catalyzed by biotin-dependent carboxylases. The hammerhead structure observed twice in BCCPsc may be regarded as the basic structural motif of biotinyl and lipoyl domains of a superfamily of enzymes. The new MAD phasing techniques developed in the course of determining this structure enhance the power of the MAD method.
Acetyl-CoA Carboxylase↗