Phenylketonuria

In this condition, there is a deficiency of phenylalanine hydroxylase. This enzyme is necessary to metabolize the amino acid phenylalanine ('Phe') to the amino acid tyrosine. However, in phenylketonuria, phenylalanine is transaminated directly by nonspecific aminotransferases to phenylpyruvate. In othr words, if this reaction does not take place, phenylalanine accumulates and tyrosine is deficient. The body needs tyrosine to build a sufficient amount of proteins, without it at a young age, it could lead to mental retardation. Recall that this is a chromosomal disorder so right from birth, you will have this deficiency in tyrosine.