The problem of maternal phenylketonuria

Mentally retarded non-phenylketonuric offspring from untreated phenylketonuric mothers have been reported upon by a number of groups. To this list we add some additional cases. These offspring commonly have lower I.Q's than their mothers. It is reasonable to postulate that the high concentrations of phenylalanine or its metabolites in the blood of the untreated mother, which is actively transported across the placenta into the blood of the infant, is the cause of the frequently severe damage to the vulnerable infant brain in utero. The fact that artificially produced high concentrations of phenylalanine in the blood of pregnant monkeys and of pregnant rats seems to have culminated in offspring with impaired learning abilities is consistent with this supposition. The results indicating apparently normal mental development, so far, in the nonphenylketonuric offspring of at least 2 phenylketonuric mothers treated with low phenylalanine diets during pregnancy, are encouraging. Because of the advent of routine screening tests for PKU in the newborn, there are an increasing number of phenylketonuric girls, treated in their early years but now on a normal diet, who are approaching the childbearing period and who are mentally normal. Consequently, there is a growing opportunity and responsibility for preventing mental retardation in their future nonphenylketonuric children. It is suggested that dietary treatment during the pregnancies of phenylketonuric mothers be seriously considered, with caution exercised so that the blood concentrations of phenylalanine in the mother under treatment be maintained above 3 but below 8 mg. per 100 ml. Routine urine testing for PKU is, therefore, recommended for all women at the first prenatal visit and at the premarital examination.