Lactulose in trimethylaminuria, the fish-odour syndrome.

We have measured the urinary excretion of trimethylamine in two sisters with trimethylaminuria (the fish-odour syndrome). On a restricted diet the patients still excreted increased quantities of trimethylamine, and this did not alter following a fourteen-day course of lactulose. Dietary provocation produced a rise in urinary trimethylamine which was abolished by fourteen days' pretreatment with lactulose. The case histories illustrate the tendency for delay in reaching this diagnosis and the psychological damage caused by the condition.

Interference by naproxen in the urinary 5-hydroxyindoleacetic acid assay is due to a metabolite, desmethylnaproxen.

Interference by naproxen in the spectrophotometric assay for urinary 5-hydroxyindoleacetic acid has been investigated. Gas chromatography-mass spectrometry demonstrated that ingestion of naproxen was associated with the production of four urinary components, unchanged drug and three metabolites, the major one being desmethylnaproxen. Unlike naproxen, this metabolite reacted in the spectrophotometric assay giving a product with the same absorption spectrum as that observed in urine samples obtained after naproxen ingestion. Unlike 5-hydroxyindoleacetic acid, the colour due to desmethylnaproxen is thermolabile and so the interference may be overcome by performing the incubation at 100 degrees C.

The analysis of thiodiglycollic acid by selected ion monitoring.

A selected ion monitoring assay for thiodiglycollic acid in urine is described. Urine samples are analysed by combined gas chromatography-mass spectrometry as their dibutyl esters using pimelic acid as an internal standard. Rapid analysis was achieved by the simplification of sample preparation. The assay has proved to be reliable, with a detection limit of less than 0.5 mumol/l. The excretion of large amounts of thiodiglycollic acid in premature babies urine has been confirmed, with the greatest excretion occurring from those neonates born with a gestational age of 30 wk or less.

Avoidable accumulation of potentially toxic levels of benzothiazoles in babies receiving intravenous therapy.

Large amounts of a compound of exogenous origin were present in the serum of premature babies receiving prolonged intravenous therapy. This compound, identified as 2-(carboxymethylthio)benzothiazole (CMB) is derived from oxidation of 2-(hydroxyethylthio)benzothiazole which is leached out of rubber components of intravenous administration sets and syringes. Serum concentrations of CMB after prolonged exposure can exceed 500 mumol/l; concentrations over 35 mumol/l were observed in 91 babies over a period of twenty-seven months. This potentially toxic accumulation can be largely avoided by judicious choice of equipment.

Concentrations of succinylacetone after homogentisate and tyrosine loading in healthy individuals with low fumarylacetoacetase activity.

Two healthy adults with low fumarylacetoacetase activity in fibroblasts and lymphocytes, one a compound heterozygote for the tyrosinaemia and the pseudodeficiency genes and the other a homozygote for the pseudodeficiency gene, produced substantial amounts of succinylacetone when given an intravenous homogentisate load. The level of metabolites correlated with the residual enzyme activity and the genotype, being higher in the compound heterozygote. This subject also showed a small increase of metabolites in urine after an oral tyrosine load. In the pseudodeficiency homozygote a depression of erythrocyte delta-aminolevulinate dehydratase activity was observed after the tyrosine load. In fasting state both individuals have erythrocyte delta-aminolevulinate dehydratase activity below the reference range, indicating a persistently raised concentration of metabolites. Thus, the pseudodeficiency state is not just an in vitro phenomenon, but results in a definite reduction of enzyme activity in vivo. We speculate that the variant gene may predispose to the development of liver disease, possibly not recognized as tyrosinaemia.

The improvement of the antenatal detection of fetal neural tube defects using discriminant analysis.

Discriminant analysis was applied to the antenatal diagnosis of fetal neural tube defects. Alpha-fetoprotein, gestational age, and seven easily assayed biochemical variables were used to generate the discriminant function, which was derived from a retrospective study on data from 130 pregnancies, including 25 which were associated with fetal anencephaly and 13 with fetal spina bifida. This function was used to generate a diagnosis in a blind study of 40 previously unassayed samples: 20 problem samples from another centre interspersed with 20 normal samples. The same function was used over a period of 2 years to predict prospectively the outcome of 669 pregnancies with respect to neural tube defects. Of these 55 were found to be associated with fetal neural tube defects. Classification is shown to be more reliable than using alpha-fetoprotein and gestational age alone. The results demonstrate a successful application of discriminant analysis to medical diagnosis.

The analysis of trimethylamine in body fluids by a direct medium resolution mass spectrometric method.

A simple, high throughput method of analysis of trimethylamine in body fluids has been developed to assist with the management of patients with the inherited metabolic disorder, trimethylaminuria. The headspace in sealed vials was analysed using perdeuterated (2H10)trimethylamine hydrochloride as an internal standard. The gas chromatograph inlet system of the mass spectrometer was adapted to suit this method of analysis. Medium resolving power was used to measure the ion ratio of the [M-H]+ ion of trimethylamine and the [M-2H]+ ion of the internal standard. The method is faster and more accurate than gas chromatographic methods. The concentrations of trimethylamine found in normal urine are similar to those reported previously.

The use of multivariate discriminant analysis in the antenatal detection of fetal neural tube defects.

Early second trimester amniotic fluid is classified by stepwise discriminant analysis involving the computer program BMDP77, based upon biochemical analyses for alpha-fetoprotein and eight other easily assayed variables. The outcome of about 800 pregnancies has been predicted on this basis, over 80 of which were associated with fetal neural tube defects. Classification is shown to be more reliable than using alpha-fetoprotein and gestational age alone. Although in practice this approach has now been superceded by the introduction of the analysis of acetylcholine-esterase isoenzyme activity in amniotic fluid, the results demonstrate a successful application of discriminant analysis to medical diagnosis.

The analysis of hexitols in biological fluid by selected ion monitoring.

The development of a selected ion monitoring assay is described for the analysis of polyols as their per-acetyl derivatives, using L-iditol as an internal standard. Concentrations of mannitol, galactitol, sorbitol and inositol have been determined in the serum, urine and amniotic fluid from women during the second trimester of uncomplicated pregnancies. Two samples of amniotic fluid from galactosaemic pregnancies showed elevated levels of galactitol, 8.1 and 7.7 mu mol l-1 compared with normal concentrations of 0.46 +/- 0.26 mu mol l-1, whereas a normal homozygous pregnancy of heterozygous parents showed normal levels.

Comparison of amino acid concentrations in amniotic fluid from fetal neural tube defective and normal pregnancies.

Amniotic fluid collected during the second trimester of pregnancy was analysed for amino acid and protein concentrations. The composition of amniotic fluid from pregnancies complicated by fetal anencephaly or spina bifida was investigated for variance from normal amniotic fluid. In spina bifida the hydroxy amino acids were raised whilst the branched chain amino acids were lower in concentration. In anencephaly the total amino acid and the protein concentrations were raised, and a wider range of concentrations for most of the amino acids was apparent.

The potential of multivariate discriminant analysis in the antenatal detection of neural tube defects.

A method is described which improves the ability to distinguish between normal and neural tube-defective fetuses in utero. Early second trimester amniotic fluid is classified by stepwise discriminant analysis based upon biochemical analysis for alpha-fetoprotein and eight other easily assayed variables; classification is more reliable than using alpha-fetoprotein and gestational age alone.