Defect in phenylketonuria-

Ans. is 'a' i.e., Phenylanine hydroxylase Phenylketonuria# It is an inborn metabolism of phenylalanine, in which there is inability of oxidation of phenylalanine0 into tyrosine.There is defective function ofphenylalanine hydroxylase Q. which may be due to : -Classical phenylketonuria (hyperphenvlalanemia ty pe I) - Deficiency of phenylalanine hydroxylase Q.Atypical phenylketonuria (Hyperphenvlalanemia type II and III) - Defect in dihydrobiopterin reductase Q.Hyperphenvlalanemia type - IV and V - Defect in dihydrobiopterin synthesis.# Phenylalanine level is raised as it can not be oxidized into tyrosine. Therefore, some minor pathways of phenylalanine metabolism become active (which does not require hydroxylase). This result in accumulation toxic metabolites of phenylalanine which include phenylpyruvate, phenylacetate, phenyllactatc. And phenylacetylglutamine. Increased excretion of phenylalanine in urine gives the urine a mousy odor Q. For detection of phenylalanine, following tests are used : -i) Guthrie's test Q : - It detect phenylalanine in the serum.ii) FeCl3Q: - It detects phenylalanine in urine. Phenylalanine gives green colour Q with FeCI3iii) 2-4 Dinitrophenol hydrazine: - Gives yellow precipitate with old urine.# The main treatment is a phenylalanine restricted diet for life.