Prognostic factors of the intellectual outcome of phenylketonurics: On and off diet

Statistical analysis was done on 49 phenylketonurics (PKUs) treated with diet and on those 33 of the 49 whose diets were discontinued. The purpose of this study was to identify prognostic factors of intellectual outcome. While on the diet, negative correlations existed between age at diet initiation, mean serum phenylalanine concentration, and IQ scores. A positive correlation was found between parental education level and subject's IQs. The IQs were lower if either the initial EEG or the last EEG was abnormal. After discontinuation of diet, longer duration of diet restriction correlated with high IQs. Initial abnormal EEG and higher concentration of serum phenylalanine after discontinuation of diet also correlated with lower IQs. Comparison of mean IQs on-diet and off-diet did not reveal any significant differences. One cannot assume any longer that early dietary management itself can be the only solution for the handicaps of PKUs nor can the IQ scores be the sole measure of their well being.