Brain damage in phenylketonuria is due to accumulation of-
Ans. is 'b' i.e., Phenylalanine "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 "Phenviaketonuriao It is an autosomal recessive disorder due to deficiency of phenylalanine hydroxylase.o As a result phenylalanine is not metabolized by hydroxylase, and metabolism is shifted to alternative pathvway and there is increased concentration of phenylalanine, phenylpyruvate, phenylacetate and phenyl-lactate.o Because phenylalanine is not converted into tyrosine, tyrosine becomes art essential amino acid.o Classical phenylketonuria is due to deficiency ofphenylalanine hydroxylase. Milder form may be caused by deficiency of dihydrobiopterin reductase that produces tetrahydrobiopterin, a cofactor for phenylalanine hydroxylase.Clinical presentationo The babies are normal at birth but may present with vomiting. Gradually mental retrardation and growth retardation develop. Baby has light complexion with blue iris. Other features are microcephaly, rash, hypertonia, seizures, exaggerated tendon reflex, wide spaced teeth, enamel hypoplasia and hyperactivity.o There is musty or mousy odour of urine and other body secretions due to presence of phenylketones.o Pregnant females with increased pheynlalanine (maternal phenylketonuria) may cause mental retardation, microcephaly, growth retardation and CHDs in babies.Diagnosiso Elevated phenylalanine levelso Elevated blood tyrosine levelo Presence of urinary metabolites of phenylalanineo Guthrie's Test - It detects the presence of phenylalanine in serumo FeCl3 - It detects the presence of phenylalanine in urine. FeCl3 is added to patients urine. If it contains phenylalanine, it will turn green.o 2-4 Dinitrophenol hydrazine - gives yellow precipitate with old urine.Treatmento Administration of low phenylalanine is the mainstay of treatment (but phenylalanine should not be completely restricted as it is necessary for growth). Tetrahydrobiopterin can be used in milder form.
Tyrosine
Phenylalanine
Tryptophan
None
Amino Acid Metabolic Disorder