Diagnosis of variants of hyperphenylalaninemia by determination of pterins in urine.

Assessment of urinary pterins is proposed as a rapid method for recognition of the variants of hyperphenylalaninemia. This is achieved by means of oxidation of pterins by iodine in acidic and alkaline solutions and then by high performance liquid chromatography on a cation-exchange column with fluorimetric detection. In biopterin-synthetase deficiency, only neopterin accumulated; in dihydropteridine-reductase (DHPR) deficiency and in phenylketonuria, high levels of pterins are found, but BH4 levels, absent in the former and high in the latter, allow a differential diagnosis. Phenylalanine loads in the controls also lead to increased elimination of pterins, but with a pattern different from that found in phenylketonuria. This method can be used before dietary treatment and thus can be proposed for all newly detected hyperphenylalaninemic babies.