Cognitive development in offspring of untreated and preconceptionally treated maternal phenylketonuria.

A survey is given of literature reports on the effect of performance in offspring from 26 maternal PKU pregnancies treated prior to conception. The survey includes two women who were referred to us for genetic counselling because they had both given birth to microcephalic, mentally retarded children. The women were discovered to suffer from unrecognized maternal PKU with fasting phenylalanine concentration of 1.1-1.5 mmol/L. A strict diet was introduced prior to planned pregnancy and after some months on diet (phenylalanine concentrations less than 0.6 mmol/L) they became pregnant again. Serum phenylalanine levels were monitored weekly throughout pregnancy, and adjustments in the diet were made to keep serum phenylalanine concentration within the range of 0.18-0.42 mmol/L. The outcome of the pregnancies were healthy children who have developed normally. Their IQs are 105 and 119 at ten and four years of age, respectively and their head circumferences are normal. Our data show that the effect of preconceptional dietary treatment was children with a normal performance, contrary to their older siblings born following untreated pregnancies. These results are in agreement with the survey of ten years' promising experiences with preconceptional treatment in maternal PKU. The data may help to motivate young PKU women to accept planned pregnancies and to encourage them to return to the strict diet, which has prevented them from being retarded.