Something's new in PKU.

Elsewhere in this issue of the Journal is an instructive illustration of Murphy's Law applied to medicine: if anything can go wrong, it will. On the basis of biochemical principles, three possible defects would allow phenylalanine to escape metabolism and accumulate to injure the immature developing brain in that paradigm of avoidable mental deficiency, classic phenylketonuria. The potential defects are the familiar one of the hydroxylating enzyme protein itself, a defect of a second enzyme that regenerates the biopterin cofactor needed in the hydroxylation and a simple deficiency of biopterin itself. Jervis1 showed that the phenylalanine hydroxylating enzyme system . . .