phenylketonuriaPronunciation: /ˌfiːnʌɪlˌkiːtə(ʊ)ˈnjʊərɪə, ˌfɛnɪl-/ (abbreviation: PKU)Definition of phenylketonuria noun [mass noun] Medicine an inherited inability to metabolize phenylalanine which, if untreated, causes brain and nerve damage. phenylketonuria in other Oxford dictionaries Definition of phenylketonuria in the US English dictionary