Phenylalanine hydroxylase deficiency, traditionally known as phenylketonuria, results in the
accumulation of phenylalanine in the blood of affected individuals and was the first inborn
error of metabolism to be identified through population screening. Early identification and
treatment prevent the most dramatic clinical sequelae of the disorder, but new
neurodevelopmental and psychological problems have emerged in individuals treated from
birth. The additional unanticipated recognition of a toxic effect of elevated maternal …