Comments on neuropsychological approaches to treatment policy issues in phenylketonuria

The effect of dietary treatment on the cognitive development of young child ren with phenylketonuria (PKU) has been studied quite extensively and it se ems clear that strict treatment should be maintained at least until the age of 10 years, as most treatment centres do in fact recommend. In contrast, there is still a lot of uncertainty and disagreement about the treatment of PKU patients over 10 years of age. Part of this is simply due to the relat ive scarcity of relevant studies. Another important part, however, has to d o with the fact that findings of different studies are often reviewed and i nterpreted without much consideration of the sometimes substantial differen ces in method, sample, and design as well as the methodological problems th at limit some of them. This not only makes it difficult to draw any conclus ions regarding the treatment of older patients, but could even lead to inco rrect conclusions. Two methodological issues that seem especially important in this respect are lack of power and the choice of tests.