Antenatal diagnosis of argininosuccinic aciduria

Use of amniotic fluid amino acids in prenatal testing for argininosuccinic aciduria and citrullinaemia

Prenatal testing of 12 pregnancies at risk for argininosuccinic aciduria due to argininosuccinate lyase (ASAL) deficiency and three pregnancies at risk for citrullinaemia due to argininosuccinate synthatase (ASAS) deficiency was performed by metabolite detection in amniotic fluid and measurement of enzyme activity in uncultured and cultured chorionic tissue and in cultured amniocytes. From our data and those of previous studies, amniotic fluid argininosuccinate measurement alone is clearly a reliable and rapid diagnostic test for both severe and mild ASAL deficiency if maternal ASAL deficiency can be excluded. For prenatal diagnosis of ASAS deficiency, however, both measurement of the amniotic fluid citrulline level and enzyme assay should be employed.

Prenatal diagnosis of inherited metabolic disorders by quantitation of characteristic metabolites in amniotic fluid: facts and future

An attempt is made to summarize as completely as possible what is known about the prenatal diagnosis of amino- and organic acidurias by direct measurement of characteristic metabolites in amniotic fluid, and to indicate which disorders can potentially be diagnosed prenatally by direct quantitation of metabolites. Furthermore, the disorders are mentioned in which the prenatal diagnosis was proven to be unsuccessful by this approach. The prenatal diagnoses of a case of propionic acidemia and a case of tyrosinemia type I in the 11th and 12th week of gestational age, respectively, are reported and the prospects of performing amniocentesis in the first trimester for prenatal diagnosis are discussed.

Prenatal diagnosis of inborn errors of metabolism with renal manifestations

Prenatal diagnosis has become increasingly important for the prevention of kidney disease due to inborn errors of metabolism. The indications for prenatal diagnosis in a specific disease depend on the degree of renal involvement and the concomitant pathology of other organs, but especially of the central nervous system. The availability of successful postnatal therapy reduces the necessity for prenatal diagnosis. The determination of enzyme activities, the demonstration of storage products in fetal tissues and the analysis of amniotic fluid components are the biochemical methods most frequently used for prenatal detection. Recently, recombinant DNA techniques have enlarged the spectrum of inherited disorders that can be diagnosed before birth.

Prospective prevention of neonatal hyperammonaemia in argininosuccinic acidura by arginine therapy

Argininosuccinic aciduria, due to deficiency of argininosuccinic acid lyase, is generally associated with severe neonatal hyperammonaemia and its neurological sequelae. The cases of two siblings with this autosomal recessive disorder are presented. Both infants were preterm and delivered by Caesarean section for maternal pre-eclampsia. The first infant was not diagnosed until after the development of severe hyperammonaemia and, despite adequate treatment with haemodialysis and arginine infusion, remained comatose for a prolonged period. At 20 months she has profound developmental delays and intellectual impairment. The second infant, whose diagnosis was made antenatally by amniotic fluid analysis, was treated with arginine infusion beginning at 32 h of life and never developed hyperammonaemia. We conclude that early recognition and prompt institution of arginine therapy is an effective regimen for the prevention of neonatal hyperammonaemia in argininosuccinic aciduria.

Stable isotope dilution analysis of orotic acid and uracil in amniotic fluid

Rapid, sensitive and accurate stable isotope dilution assays were developed for the measurement of orotic acid and uracil in amniotic fluid. The method utilizes [15N2]orotic acid and [15N2]uracil as internal standards, isolation by liquid partition chromatography and quantitation by chemical ionization selected ion monitoring gas chromatography-mass spectrometry. Orotic acid at a concentration of 0.26 +/- 0.05 mumol/l and uracil at a concentration of 0.55 +/- 0.13 mumol/l were detectable in normal amniotic fluid. As affected fetuses with argininosuccinate synthetase or ornithine carbamoyl transferase deficiency showed no significant elevation of orotic acid and/or uracil in their surrounding amniotic fluids, this method unfortunately seemed not to be useful for prenatal diagnosis of these inherited disorders. Nevertheless, it provides significant advantage over available methods for the quantitation of orotic acid and uracil in which the analysis of these compounds must be very accurate, highly specific and sensitive (e.g. detection of heterozygosity for ornithine carbamoyl transferase deficiency).

Hyperammonemia

A symptomatic elevation in plasma ammonium concentration, termed hyperammonemia, is associated with numerous congenital and acquired conditions (Table 11). In some cases, such as urea cycle disorders, ammonia is the principal toxin. In other instances, such as portal systemic encephalopathy, it is but one of a number of metabolic disturbances, However, in either case hyperammonemic episodes should be treated aggressively to prevent coma, subsequent brain damage, or death. This involves restricting protein intake, providing adequate calories, and giving agents that remove accumulated nitrogen. Long-term therapy relies on diagnosing the specific disease rate. This rarely requires invasive procedures such as liver biopsy. In most cases measurement of plasma amino acids and urinary organic acids will identify the defect. Treatment involving restriction of nitrogen intake, vitamin supplementation, or stimulation of alternative pathways of waste nitrogen excretion can then be instituted. Early therapy, especially in patients with neonatal-onset hyperammonemia, is imperative to avoid severe brain damage. On this basis, the plasma ammonium level should be determined in virtually every newborn with lethargy, hypotonia, poor feeding, seizures, and/or respiratory distress of unclear origin (Table 12).

Prenatal diagnosis of citrullinemia: elevated levels of citrulline in the amniotic fluid in the three affected pregnancies

In three pregnancies at risk for citrullinemia affected fetuses were predicted both by strongly increased levels of citrulline in the amniotic fluid and by the reduced incorporation of 14C-citrulline into TCA-precipitable material in cultured amniotic fluid cells. The prenatal diagnoses of affected fetuses were confirmed after termination of the pregnancies by direct and indirect assays of argininosuccinate synthetase in the fetal livers and fibroblasts respectively. Measurement of the citrulline concentration in amniotic fluid appears to be a valuable adjunct in the prenatal diagnosis of citrullinemia.

Variation in argininosuccinate synthetase activity in amniotic fluid cell cultures: implications for prenatal diagnosis of citrullinemia

Argininosuccinate synthetase activity was measured in amniotic fluid cells cultured from 25 normal fetuses and from 2 fetuses at risk for citrullinemia. Among the 25 control lines, argininosuccinate synthetase was low in epithelial-like cultures and high in more fibroblast-like cultures. The radioactivity incorporated from 14C-citrulline into protein was proportional to argininosuccinate synthetase activity. The activity of argininosuccinate lyase, the next enzyme in the urea cycle, was unaffected by a predominance of one or the other cell type. Argininosuccinate synthetase was low but detectable in cells from the two fetuses at risk for citrullinemia. The pregnancies were continued and both resulted in clinically normal females. Thus factors such as predominant cell type may affect area cycle enzyme activity in cultured amniotic fluid cells and should be taken into consideration in attempts to diagnose citrullinemia prenatally.

Prenatal diagnosis--a compilation of diagnosed conditions

This article provides physicians with an up-to-date listing of 182 fetal conditions diagnosed prenatally. This information is presented in two key tables: the first an alphabetical listing of the conditions and the second a grouping of them according to disease categories. The latter table also presents the technique(s) used to establish the diagnosis, as well as pertinent references. Chromosomal abnormalities, diagnosed from amniotic fluid cell karyotypes, have not been individually tabulated in either table. Current techniques utilized for prenatal diagnosis are presented (see Comment).

A comprehensive screening method for detecting organic acidurias and other metabolic diseases in acutely sick infants and children

A protocol is described for the comprehensive screening of acutely ill neonates and infants for inherited metabolic diseases, with particular reference to the organic acidurias. A group of simple initial tests provide positive pointers to metabolic disorders, leading to comprehensive screening tests for the aminoacidopathies and organic acidurias. Specimen chromatograms of urinary organic acids in the normal neonate, infant, and child, obtained using the methods described, are given and compared with that from the urine of a child with previously unreported 2-hydroxyglutaric aciduria. The place of the scheme in the management of inherited metabolic disease in the perinatal period and its relationship to other screening programmes are discussed. It is estimated that use of the protocol would allow the detection of about one-half of the known inborn errors of metabolism, including the aminoacidopathies, the organic acidurias, the hyperammonaemias, and several disorders of carbohydrate metabolism, many of which present acutely in the neonate and infant.