Collaborative study of children treated for phenylketonuria: study design.

Studies that have attempted to test the effectiveness of treatment in phenylketonuria (PKU) have been handicapped by small samples due to rarity of the disorder and inadequate control of other sources of error. The present study was designed to overcome these limitations by treating a large number of children with PKU under controlled conditions from near birth to 6 years of age. Nineteen medical centers in 13 states have participated in the study, which is currently in progress. This article is one of a series of final reports. It describes the study design and sampling procedures employed to answer questions of interest for which results will be reported in subsequent articles. The study serves as a model for future collaborative investigations of a similar nature.