Organic acidurias: approach, results and clinical relevance

Routine gas chromatographic/mass spectrometric analysis of urinary organic acids. Results over a three-year period

Organic acidaemias are an important part of inborn errors of metabolism. The biochemical diagnosis is based on gas chromatographic/mass spectrometric identification of urinary organic acids. Since 1973 we have used gas chromatographic analysis of the methyl esters of urinary organic acids. Mass spectral identification was performed only when an abnormal gas chromatographic profile was suspected. In 1983 we introduced routine gas chromatographic/mass spectrometric analysis organic acids. More than 1500 urine samples from 1000 children have been analysed and we encountered more than 40 abnormal profiles: 18 classical organic acidaemias (propionic, methylmalonic, isovaleric, glutaric type I and 3-hydroxy-3-methyl glutaric acidaemias); 6 aminoacidopathies with excretion of branched chain keto acids (leucinosis) or succinylacetone (tyrosinosis type I); 14 massive dicarboxylic acidurias with excretion of suberyl and hexanoyl glycine and deficiency of the medium chain acyl CoA dehydrogenase in four patients. The use of gas chromatography/mass spectrometry routinely allows the identification of abnormal metabolites excreted in small amounts: beta-methyl-crotonyl glycine indicative of biotin deficiency: gamma-hydroxybutyric acid; and 3-methyl-glutaconic + 3-methy-glutaric acid is in a 3-methyl-glutaconic aciduria type II. Abnormal profiles due to metabolites of drugs as valproate, salicylate and barbiturate can be recognized immediately. This simple gas chromatographic/mas spectrometric system can lead to diagnosis, in one day, of rare but severe diseases needing a specific and early treatment.

The routine investigation of urinary organic acids in selected paediatric patients: results over a 2 1/2-year period

Over a 2 1/2-year period 13 patients with inborn errors of organic acid metabolism, excluding undifferentiated lactic acidosis, have been diagnosed in our laboratories. The diagnostic yield in patients who had not previously been investigated by organic acid chromatography was 1 in 25, the majority of cases having presented with metabolic acidosis. A larger number of non-specific abnormalities were also detected. This type of investigation is beset with pitfalls and is extremely labour intensive.