<prompt> The enzyme deficient in Phenyl Ketonuria is:Phenylalanine dehydrogenasePhenylalanine hydroxylaseTyrosine hydroxylaseDihydrobiopted n  <response>: Ref: Harpers illustrated Biochemistry, 28th editionExplanation: See figure belowTetrahydro biopterin H4B dependent reaction.In case of deficiency of phenyl alanine hydroxylase, phenyl alanine is converted in to phenylpyruvate phenylacetate. accumulation of which results in phenyl ketonuria. FeaturesMental retardationLight color skin hairEczema seizures Plasma phenylalanine Phenylacetate phenyl pyruvate in urineTreatment consists of limiting phenylalanine intake to levels barely adequate to support growth. Tyrosine, an essential nutrient for individuals with phenylketonuria, must be supplied in the diet. 