In this issue of AJDC, the Writing Committee of the Collaborative Study of Children Treated for Phenylketonuria reports the status of 95 of these children who have reached age 12 years, a milepost age in the study.1 At this point in the study, there were no surprises. However, the study has documented even more conclusively that (1) the sooner the low phenylalanine diet is begun, the better the outcome; (2) the longer a normal blood phenylalanine level is maintained, the better the outcome; and (3) termination of the diet has a deleterious effect. Because this collaborative study appears to be ending, I fear that it will be terminated prematurely.
This carefully designed study was straightforward in concept and adequate for the knowledge and psychologic testing instruments of 1967. The planners underestimated the difficulty of maintaining near-normal blood phenylalanine levels in the 200 or more affected