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Screening newborns for multiple organic acidurias in dried filter paper urine samples: method development.

Screening urine for inherited and acquired organic acidurias in newborns has the potential of preventing severe disease, mental retardation, and death. A method for screening dried urine filter paper samples for acidic markers of at least 20 different metabolic conditions has been developed. These conditions include, among others, maple syrup urine disease; methylmalonic, propionic, isovaleric, glutaric, and hydroxymethylglutaric acidurias; methylcrotonylglycinuria; medium-chain acyl-CoA dehydrogenase deficiency; inherited vitamin responsive disorders B12, biotin, B2), and acquired deficiencies of these vitamins. The preparation of the urine extract is identical to the method we use to screen infants for neuroblastoma. Screening is based on a highly sensitive and specific determination of eight organic acid markers by an automated computerized gas chromatography mass spectrometry system using selected ion monitoring. The markers used for screening are methylmalonic acid, 2-hydroxyisocaproic acid, glutaric acid, propionylglycine, isovalerylglycine, 3-methylcrotonylglycine, hexanoylglycine, and 3-phenylpropionylglycine. The extraction efficiencies of these acids from dried filter paper were similar to extraction from water, ranging from about 40% to 80%, except for propionylglycine which showed a low extraction efficiency of 11-13%. The stability of these acids on filter paper exposed to room air and temperature over a period of 15 d was adequate for the use of this collection method for organic aciduria screening. Normal levels, adjusted to urinary creatinine, were established for these acids in 519 urine filter paper samples obtained from 3-wk-old newborns. This screening method was tested on samples obtained from 12 patients with known organic acidurias including stored urine filter paper collected at 3-wk of age from two infants later found to have organic acidurias.

Amino Acids↗

Absence of argininosuccinate lyase protein in the liver of two patients with argininosuccinic aciduria.

The enzyme defects in two cases of argininosuccinic aciduria were examined at the molecular level by enzymatic and immunological methods. No argininosuccinate lyase activity was detected in the liver or erythrocytes of either patient nor in the kidney or brain of one of the patients even in the presence of high concentrations of the substrate. The titration curve of antiserum to human argininosuccinate lyase with the liver extract from a control subject was not affected by the addition of the liver extracts from one of the patients. Double immunodiffusion analysis revealed a single precipitin line between the purified antiserum and the liver extract from a control, but no precipitin lines between the antisera and the liver extracts from the two patients. These results indicate a complete or almost complete defect of an immunologically cross-reactive material in the liver of the patients.

Amino Acid Metabolism, Inborn Errors↗

[Argininosuccinic aciduria. A new case revealed by psychiatric disorders].

The case of a 4 years old boy, hospitalized for an unexplained coma, is reported. He is the first child of a non-consanguin couple. The psychomotor development of this child was considered as normal up to the age of 18 months; then, a delay in language development, behaviour disorders with an important instability interrupted by episodes of somnolence, were observed. This child was treated for psychotic disorders. At the age of 3 and half, he had two episodes of seizures associated with fever. He was hospitalized for a 24 hours coma (4 years old). An hepatomegaly and a dry, brittle hair were then observed. Hyperammonemia was made obvious by a protein tolerance test. The diagnosis of argininosuccinate lyase (ASAL) deficiency was based on the increased levels of ASA in plasma and urine. The deficiency was proved by a fibroblast culture. With protein restriction, hepatomegaly disappeared, hair became normal, the behaviour disorders and the delay in language development was improved. However, some school difficulties persist. This case shows that an hereditary metabolic syndrome can be revealed by psychotic like symptoms in childhood.

Amino Acid Metabolism, Inborn Errors↗

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.

Animals↗

Mild orotic aciduria and uricosuria in severe trauma victims.

Hypermetabolic responses with respect to pyrimidine and purine kinetics in trauma victims were investigated during the catabolic phase before and after nutritional support. Orotic acid and uric acid excretions were measured in 32 adult, severely traumatized, hypermetabolic, and highly catabolic patients while they were receiving fluids with no calories or nitrogen. Patients were then fed intravenously amino acids and glucose or glucose alone or fed enterally for 5-6 d. Daily excretions of orotic acid, uric acid, urea, nitrogen, and creatinine were monitored. Mild orotic aciduria and uricosuria with hypouricemia were the basal-trauma responses. The significant (P = 0.001, r = 0.70) positive correlation between orotic and uric acid excretion demonstrates the parallelism between pyrimidine and purine metabolism. Feeding for 5-6 d could decrease but not readily abolish the injury-induced metabolic changes in nitrogen, pyrimidine, and purine metabolism. Glucose infusion alone may be sufficient to counteract the metabolic effects of trauma in the early flow phase of injury.

Adult↗

Diagnosis and therapy of organic acidurias.

Organic acidurias are a group of numerous inherited metabolic disorders with an involvement of different pathways of the amino acid, carbohydrate and lipid metabolism. Many diseases have their onset with an acute metabolic crisis in the newborn period. The most important diagnostic investigation is organic acid analysis of urine by gas chromatography-mass spectrometry. Because specific clinical signs are lacking, a selective screening procedure is recommended. Diagnosis and therapy should be aggressive, since prognosis of many disorders is related to early diagnosis and specific therapeutic measures. These include long term management with protein restriction, supplementation with special amino acid mixtures and carnitine. In our experience continuous arteriovenous hemofiltration has turned out to be a very effective detoxification method during acute metabolic crisis of the newborn. Long term follow up and therapy control is very important for the outcome of the patients. Measurement of odd long chain fatty acids (OLCFA) in erythrocyte membranes has proved to be a good control parameter of the metabolic condition of children with disorders of the branched-chain amino acid metabolism.

Amino Acid Metabolism, Inborn Errors↗

Accumulation of odd-numbered long-chain fatty acids in fetuses and neonates with inherited disorders of propionate metabolism.

Fetuses affected with propionic acidemia incorporate great amounts of odd-numbered long-chain fatty acids (OLCFA) into their body lipids. This is due to abundant supply with precursor amino acids of propionyl-CoA throughout pregnancy. After birth, the lower provision of precursor amino acids during dietary treatment compared with fetal life results in a decline of propionyl-CoA production and therefore OLCFA synthesis. However, the observed decrease of OLCFA may also partly reflect the recovery from acute ketoacidotic episodes that the patients experienced soon after birth as long as they were undiagnosed. In a patient with vitamin B12-responsive methylmalonic aciduria treated prenatally with large doses of vitamin B12 given to the mother, the cord plasma lipids contained normal amounts of OLCFA. This indicates that prenatal therapy led to an increased flux of propionyl-CoA through the defective methylmalonyl-CoA mutase step. Thus, in addition to the quantification of a decline in methylmalonic acid in maternal urine, OLCFA in cord blood lipids might be a further parameter for evaluating prenatal treatment in patients with vitamin B12-responsive methylmalonic aciduria.

Acyl Coenzyme A↗

Argininosuccinic aciduria: long-term treatment with arginine.

The presentation and 2 year treatment of a patient with argininosuccinic aciduria is reported. Erythrocyte argininosuccinate lyase activity was less than 2% of normal. Long-term management included protein restriction and arginine dietary supplementation. The child experienced three episodes of hyperammonaemia (greater than 100 microns), the first at birth, the second at 6.5 months and the third at 16 months. Neurological development deteriorated between 14 and 24 months. Hepatomegaly and biochemical hepatitis, a feature of this condition, was accompanied by enlarged mitochondria with tubular paracrystalline inclusions not previously recognized in this disorder.

Amino Acid Metabolism, Inborn Errors↗

SLC7A7, encoding a putative permease-related protein, is mutated in patients with lysinuric protein intolerance.

Lysinuric protein intolerance (LPI, MIM 222700) is an autosomal recessive multisystem disorder found mainly in Finland and Italy. On a normal diet, LPI patients present poor feeding, vomiting, diarrhoea, episodes of hyperammoniaemic coma and failure to thrive. Hepatosplenomegaly, osteoporosis and a life-threatening pulmonary involvement (alveolar proteinosis) are also seen. LPI is caused by defective cationic amino acid (CAA) transport at the basolateral membrane of epithelial cells in kidney and intestine. Metabolic derangement is characterized by increased renal excretion of CAA, reduced CAA absorption from intestine and orotic aciduria. The gene causing LPI was assigned using linkage analysis to chromosome 14q11.2 near the T-cell receptor alpha/delta chains locus, and a critical region has been defined. We have identified two new transcripts (SLC7A8 and SLC7A7) homologous to amino acid transporters, highly expressed in kidney and mapping in the LPI critical region. Mutational analysis of both transcripts revealed that SLC7A7 (for solute carrier family 7, member 7) is mutated in LPI. In five Italian patients, we found either an insertion or deletion in the coding sequence, which provides evidence of a causative role of SLC7A7 in LPI. Furthermore, we detected a splice acceptor change resulting in a frameshift and premature translation termination in four unrelated Finnish patients. This mutation may represent the founder LPI allele in Finland.

Amino Acid Metabolism, Inborn Errors↗

Cloning, sequencing and expression of rat liver 3-phosphoglycerate dehydrogenase.

Rat liver d-3-phosphoglycerate dehydrogenase was purified to homogeneity and digested with trypsin, and the sequences of two peptides were determined. This sequence information was used to screen a rat hepatoma cDNA library. Among 11 positive clones, two covered the whole coding sequence. The deduced amino acid sequence (533 residues; Mr 56493) shared closer similarity with Bacillus subtilis 3-phosphoglycerate dehydrogenase than with the enzymes from Escherichia coli, Haemophilus influenzae and Saccharomyces cerevisiae. In all cases the similarity was most apparent in the substrate- and NAD+-binding domains, and low or insignificant in the C-terminal domain. A corresponding 2.1 kb mRNA was present in rat tissues including kidney, brain and testis, whatever the dietary status, and also in livers of animals fed a protein-free, carbohydrate-rich diet, but not in livers of control rats, suggesting transcriptional regulation. The full-length rat 3-phosphoglycerate dehydrogenase was expressed in E. coli and purified. The recombinant enzyme and the protein purified from liver displayed hyperbolic kinetics with respect to 3-phosphoglycerate, NAD+ and NADH, but substrate inhibition by 3-phosphohydroxypyruvate was observed; this inhibition was antagonized by salts. Similar properties were observed with a truncated form of 3-phosphoglycerate dehydrogenase lacking the C-terminal domain, indicating that the latter is not implicated in substrate inhibition or in salt effects. By contrast with the bacterial enzyme, rat 3-phosphoglycerate dehydrogenase did not catalyse the reduction of 2-oxoglutarate, indicating that this enzyme is not involved in human D- or L-hydroxyglutaric aciduria.

Alcohol Oxidoreductases↗