Brain damage in phenylketonuria is due to accumulation of ?

"The primary symptom of untreated phenylketonuria (i.e. mental retardation) is the result of consuming foods that contain phenylalanine, which is toxic to brain tissue"PhenylaketonuriaIt is an autosomal recessive disorder due to deficiency of phenylalanine hydroxylase.As a result phenylalanine is not metabolized by hydroxylase, and metabolism is shifted to alternative pathyway and there is increased concentration of phenylalanine, phenylpyruvate, phenylacetate and phenyl-lactate. Because phenylalanine is not conveed into tyrosine, tyrosine becomes an essential amino acid.Classical phenylketonuria is due to deficiency of phenylalanine hydroxylase. Milder form may be caused by deficiency of dihydrobiopterin reductase that produces tetrahydrobiopterin, a cofactor for phenylalanine hydroxylase.Clinical presentationThe babies are normal at bih but may present with vomiting. Gradually mental retrardation and growth retardation develop. Baby has light complexion with blue iris. Other features are microcephaly, rash, hypeonia, seizures, exaggerated tendon reflex, wide spaced teeth, enamel hypoplasia and hyperactivity.There is musty or mousy odour of urine and other body secretions due to presence of phenylketones.Pregnant females with increased pheynlalanine (maternal phenylketonuria) may cause mental retardation, microcephaly, growth retardation and CHDs in babies.