A woman with phenylketonuria gave birth to an infant with a cardiac defect and microcephaly despite introduction of a low-phenylalanine diet 5 weeks after conception (3 weeks after the first missed period). In maternal phenylketonuria fetal damage leading to reduced brain growth and cardiac malformations probably occurs within a few weeks of conception.

Ten children have been born to five parents (four female, one male) with cystathionine synthase deficient homocystinuria. All the patients were pyridoxine responsive. The children are well except for one with Down's syndrome. Eight of the 10 children have no homocystine in the blood or urine and must be heterozygotes. The other two have small amounts of homocystine, and their genetic status is uncertain. The results are encouraging with regard to pregnancy and its outcome, but it is emphasised that the results might be very different in patients who do not respond to pyridoxine and become pregnant having high plasma methionine and homocystine values.