Diseases of phenylalanine metabolism

Continuing investigation of the system that hydroxylates phenylalanine to tyrosine has led to new insights into diseases associated with the malfunction of this system. Good evidence has confirmed that phenylketonuria (PKU) is not caused by a simple lack of phenylalanine hydroxylase. Dihydropteridine reductase deficiency as well as defects in biopterin metabolism may also cause the clinical features of phenylketonuria. Furthermore, these diseases do not respond to the standard treatment for phenylketonuria.