Classical citrullinaemia is caused by the inherited deficiency of argininosuccinate synthetase. Although varying degrees of liver involvement have been observed in urea cycle defects, including classical citrullinaemia, the co-existence of liver failure in a patient heterozygous for the disease has not been reported before. A female infant was investigated to find out the aetiology of early infantile liver failure. She was later found to be a heterozygote for the G390R mutation found in severe citrullinaemia patients.
Conclusion: Classical citrullinaemia is a phenotypically heterogeneous disease, and observations for signs of its presence should be made even in heterozygotes.