Dihydroxanthopterinuria in phenylketonuria and lethal hyperphenylalaninemia patients

7,8-Dihydroxanthopterin in identified in urine from phenylketonuria and lethal hyperphenylalaninemia patients. Because 7,8-dihyroxanthopterin is readily oxidised to xanthopterin, most of the characterisation was performed on xanthopterin. This finding indicates a gross disturbance of tetrahydrobiopterin metabolism in these patients. 7,8-dihydroxanthopterin or a related pterin may play a role in the pathogenesis of neurological symptoms in phenylketonuria and lethal hyperphenylalaninemia.