PHENYLKETONURIA

The dietary regimen is a difficult one; it must be closely controlled by the physician if complications are to be avoided. Although effective in limiting pathology, if administered early and maintained, evidence is not yet presented as to whether it is fully protective. Estimates of the incidence and prevalence of phenylketonuria are not well established. There are indications that, although rare, the incidence may be considerably higher than the 1 in 20,000 to 25,000 births previously estimated. Discrepancies in the estimates should be explored for possible explanation. These may relate to different population frequencies, definitions of mental retardation, and screening and testing procedures. The degree of variability in the manifestations (or expressivity) of phenylketonuria in mental retardation and other effects has not been adequately examined. Investigation of the factors relating to this variability may provide information regarding the mechanics of pathology and lead to improved screening and therapeutic measures.