Prenatal diagnosis of bovine citrullinaemia

Holstein/Friesian embryos, progeny of citrullinaemia heterozygotes, were transferred to recipient cows. The citrullinaemia genotype of the fetus/calf was established, at birth, by estimation of citrulline concentration in plasma or by analyses of argininosuccinate synthetase exon 5 sequences in DNA from blood leucocytes. Between 115 and 125 days of gestation amniotic fluid was collected transabdominally from nine recipient cows. The mean citrulline concentration in amniotic fluid from fetuses unaffected with citrullinaemia was 28 microM, SD 9 and range 15 to 38 microM. Citrulline concentration was 107 and 130 microM in amniotic fluid from two fetuses homozygous for the citrullinaemia mutation. Only the normal bovine citrullinaemia sequence was detected in cells cultured from amniotic fluid taken from two homozygous normal and two heterozygous fetuses. Both normal and mutant sequences were found in cells cultured from amniotic fluid collected from three of five heterozygous fetuses. Only the mutant sequence was found in cells cultured from the two citrullinaemia affected fetuses. MHC class II DRB3 haplotyping revealed that in four instances cultured cells were from the surrogate mother, not the fetus, these included samples from two heterozygotes in which only the normal sequence was detected in amniotic fluid.