A 5-year-old boy, excreting large amounts of 2-hydroxyglutaric acid in the urine (3.3-7.6 mmol/l), is described. The patient presented with psychomotor retardation and dystrophy. His skeletal age was delayed. The EEG was not well differentiated; it resembled that observed in 2-year-old children. There was a severe anaemia, which reacted well to iron supplements. The 2-hydroxyglutaric acid was found to have the L-configuration, as analysed by capillary gas chromatography of the O-acetylated di-(-)-2-butyl ester derivative. The relation of L-2-hydroxyglutarate excretion to known metabolic pathways is discussed.

Monoamine oxidase (MAO) exists as two isoenzymes and plays a central role in the metabolism of monoamine neurotransmitters. In this study we compared the neurochemical phenotypes of previously described subjects with genetically determined selective lack of MAO-A or a lack of both MAO-A and MAO-B with those of two subjects with a previously described X chromosome microdeletion in whom we now demonstrate selective MAO-B deficiency.

Fatty acids are a major source of metabolic fuel in man. Both mitochondria and peroxisomes are capable of fatty acid fl-oxidation (Schulz, 1985). It is generally agreed that the oxidation of medium and long chain fatty acids, which are most abundant in our daily diet, takes place predominantly in mitochondria. In contrast, peroxisomal fl-oxidafion is not so important for energy purposes, but catalyses the chainshortening of a distinct set of substrates which includes very long chain fatty acids, certain mono-and polyunsaturated fatty acids and di-and trihydroxycholestanoic acid (see Wanders et al., 1990 for review). The different physiological functions of mitochondrial and peroxisomal fl-oxidation are reflected in the widely differing clinical consequences of defects in mitochondrial and peroxisomal fl-oxidation, respectively. In recent years an increasing number of inherited diseases in man have been recognized in which there is an impairment in mitochondrial fl-oxidation (Vianey-Liaud et al., 1987). In this paper we report the identification of a new inborn error of mitochondfial fi-oxidation at the level of long chain 3-hydroxyacyl-CoA dehydrogenase in a child who presented at 5 months of age with diarrhoea and vomiting, subsequently followed by increasing lethargy which appeared to be associated with hypoketotic hypoglycaemia. MATERIALS AND METHODS Enzyme activity measurementsThe activity of 3-hydroxyacyl-CoA dehydrogenase was measured in homogenates of cultured skin fibroblasts at 37°C by following the decrease in absorbance at 311

A condition called thymine uracilurea has been described that is due to a lack of dihydropyrimidine dehydrogenase (DPD) activity. Cancer patients experiencing acute 5-fluorouracil toxicity also have lower-than-normal DPD activities. However, to date, the molecular basis of this disorder has not been addressed. In this study, the phenotype and genotype of a family that presents a patient showing no DPD activity was determined. Fibroblast mRNAs from the patient and four family members were subjected to reverse transcriptase polymerase chain reaction (RT-PCR) using primers generated from the human DPD cDNA sequence. DPD mRNA from the patient was found to lack a segment of 165 nucleotides that results from exon skipping. DPD mRNA from the parents and a sibling were found to be heterozygous for the deleted and the normal mRNA, while a brother had two normal transcripts. DPD activities and levels of DPD protein correlated with genotype; the deficient patient had no detectable DPD protein. PCR analysis of the genomic DNA from this family revealed that the defective mRNA is not due to a deletion of a portion of the gene that contains the exon, thus implying that the mutation is the result of an as yet nonidentified point mutation that causes faulty splicing.

In recent years tremendous progress has been made with respect to the enzymology of the mitochondrial fatty acid beta-oxidation machinery and defects therein. Firstly, a number of new mitochondrial beta-oxidation enzymes have been identified, including very-long-chain acyl-CoA dehydrogenase (VLCAD) and mitochondrial trifunctional protein (MTP). Secondly, the introduction of tandem MS for the analysis of plasma acylcarnitines has greatly facilitated the identification of patients with a defect in fatty acid oxidation (FAO). These two developments explain why the number of defined FAO disorders has increased dramatically, making FAO disorders the most rapidly growing group of inborn errors of metabolism. In this review we describe the current state of knowledge of the enzymes involved in the mitochondrial oxidation of straight-chain, branched-chain and (poly)unsaturated fatty acyl-CoAs as well as disorders of fatty acid oxidation. The laboratory diagnosis of these disorders is described, with particular emphasis on the methods used to identify the underlying enzyme defect and the molecular mutations. In addition, a simple flowchart is presented as a guide to the identification of mitochondrial FAO-disorders. Finally, treatment strategies are discussed briefly.