Genetic implications for newborn screening for phenylketonuria

With the advent of newborn screening and institution in the newborn period of a diet with restricted amounts of phenylalanine, some of the phenotypic features of phenylketonuria, including impaired cognitive development, can be averted. The success of newborn screening has resulted in many intellectually capable women with phenylketonuria who are now of childbearing age and are at risk of exposing their fetus to toxic levels of phenylalanine in utero resulting in mental retardation, microcephaly, and congenital heart disease in the offspring. The earlier in pregnancy that a diet low in phenylalanine is initiated and maintained, the better the reproductive outcome.