Citrullinaemia: The possibility of prenatal diagnosis

Argininosuccinate synthetase activity in amniotic fluid cells from a fetus at risk for citrullinaemia was low compared to the activity in amniotic fluid cells from a normal fetus, but five times the activity in fibroblasts from a patient with citrullinaemia. These enzyme values indicated a normal or heterozygous fetus. Chromosome analysis of the amniotic fluid cells from the fetus at risk, however, showed an unusual X/20 translocation. As we could not guarantee the delivery of a normal child, the parents chose to have a therapeutic abortion. Argininosuccinate synthetase activity in the liver and kidney of the aborted fetus was in the normal and heterozygous range respectively, confirming the prenatal diagnosis. The activity in the father's fibroblasts was low, less than 10% of normal. The difficulty of interpreting the results of prenatal diagnosis in such a family and the importance of studying parental cells are discussed.