Fetal tissue amino acid concentrations in argininosuccinic aciduria and in "maternal homocystinuria".

Free amino acid concentrations have been measured in the tissues of a fetus at risk for argininosuccinic aciduria and of an obligate heterozygous fetus in a mother homozygous for homocystinuria. Argininosuccinic acid was detected in all tissues studied of the homozygous affected fetus from the heterozygous mother. Abnormal concentrations of methionine and cystathionine were observed in the tissues of the fetus who was an obligate heterozygote for homocystinuria. These abnormal free amino acid concentrations occur early in fetal development and may be related to later brain dysfunction.