Abnormal mRNA for argininosuccinate synthetase in citrullinaemia

Citrullinaemia is a human inborn error of metabolism resulting from the deficiency of argininosuccinate synthetase. In a previous study of cultured skin fibroblasts from citrullinaemia patients, we showed that the presumed defects in DNA were not detectable by Southern blotting analysis, and that only 2 of 11 cell lines contained detectable enzyme antigen. All citrullinaemia cell lines contained hybridizable mRNA but slight size heterogeneity was noted. Here we report the extension of the analysis of the RNA using S1 nuclease mapping techniques. Among six cell lines examined, five showed an abnormality of mRNA detectable by S1 nuclease analysis. The data indicate that a minimum of three out of five non-consanguineous patients represent compound heterozygotes. The S1 nuclease detectable defects may represent deletions or rearrangements in the genomic DNA, or more probably represent examples of abnormal RNA splicing. The approach used here is useful for molecular analysis of genetic defects, for prenatal diagnosis, and for study of genetic variation.