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Ornithine carbamoyltransferase (OCT) is a liver-specific enzyme located in the mitochondrial matrix. OCT deficiency is an X-linked disease with a heterogeneous phenotype, even in affected males. We studied two male patients (K.M., K.G.) with early and late onset, respectively. OCT activity was zero in the autopsied liver of patient K.M. and was 6% of control in the biopsied liver of K.G. Sequencing of OCT cDNAs revealed exon 5 skipping in K.M., resulting from a T-to-C transition of the initial dinucleotide of the 5' splicing donor site of intron 5, and a G-to-T transversion at position +45 in exon 9 (L304F) in K.G., providing three OCT mRNAs of different lengths: a normally spliced transcript, 23 bp insertion of intron 8 and the first 50bp missing within exon 9. Exon 5 skipping and two other aberrant splicings produced stop codons early downstream in mature OCT mRNAs. Expression study of a missense allele, L304F, transfected to cultured Cos 1 cells revealed a 34.4% value of the control. The difference of OCT activities between the patient liver and transfected cells (6% vs. 34%) can be explained by this splicing abnormality.

Abstract: Argininosuccinate (ASA) synthetase in the liver from a patient with a variant form of citrullinaemia was analysed. Serum citrulline level was approximately 40 times higher than the control level, and the ASA synthetase activity was approximately 10% that of the control. Other urea cycle enzymes were within normal ranges. The specific activity (enzyme activity/enzyme protein, measured by immunochemical method), pH optimum, Michaelis constants, and thermal denaturation in the presence or absence of ASA were similar to those in enzymes obtained from the normal and the patient's liver cells. Noin vitro effect of the patient's liver homogenate on ASA synthetase in normal liver was observed. Serum citrulline levels of the patient's parents and young brother were at the maximal level of control at fasting and definitely elevated 4 h after citrulline loading (100 mg/kg).

We examined the DNA in two families with ornithine transcarbamoylase (OTC) deficiency. Two point mutations of the OTC gene, a C-to-T (codon 141) and a G-to-A (codon 141), were identified. This allowed prenatal monitoring to be made for two fetuses in each family, using polymerase chain reaction (PCR), followed by allele-specific oligonucleotide hybridization orTaqI digestion of amplified sequence. The diagnoses showed heterozygotes of a wild type gene and the corresponding mutant gene in these fetuses; each was confirmed postnatally.

Summary: Maple syrup urine disease (MSUD) is an autosomal recessive inherited disease due to a deficiency of any of the subunits, E1agr, E1beta or E2, of the branched-chain agr-ketoacid dehydrogenase complex (BCKDH). A large Mennonite kindred of MSUD has been studied in Pennsylvania, USA. In the present investigation, genomes from 70 members, including 12 patients belonging to eight different Mennonite MSUD pedigrees, were examined for possible abnormalities in the E1agr gene of BCKDH, by primer-specified restriction map modification. A T-to-A substitution which generates an asparagine in place of a tyrosine at amino acid 394 of the mature E1agr subunit was present in both alleles in all the patients and in a single allele in all obligate carriers and several siblings. We describe a new technique for rapid and easy detection of the mutant gene in this population. These family studies provide additional evidence that Mennonite MSUD is caused by a missense mutation of the E1agr gene of BCKDH.

Pyruvate dehydrogenase complex was studied using bio- and immunochemical methods in cultured cells derived from two patients with the severe type and one patient with the mild type of pyruvate dehydrogenase complex deficiency. In patients 1 and 2, enzyme activity was all but undetectable and associated with the absence of E1asubunit of the complex. Patient 3 had a slightly reduced level of enzyme activity, and this was associated with a larger form of E1asubunit. The amount and size of E1amRNA in the three patients was similar to that of control samples. Thus, the severity of E1adeficiency in these three patients is likely to depend on the type of mutation in the pyruvate dehydrogenase E1asubunit and the synthesis and degradation rate of the subunit.

The biochemical nature of the pyruvate dehydrogenase complex (PDHC) in muscle was studied in a patient with pyruvate dehydrogenase complex deficiency. The enzyme activity was approximately 30% of the control level and the apparentKmvalue of the enzyme was similar to the control value. The immunoblot pattern of each subunit protein, E1a, E1ß, the component X, E2and E3, was comparable to that of the control on both one-and two-dimensional electrophoresis, the staining of each subunit protein being reduced in intensity, corresponding to the reduced enzyme activity. The enzyme deficiency is likely to be quantitative rather than qualitative, although the actual mechanism is unknown.