[Hyperphenylalaninemia in 1981. A diagnostic approach (author's transl)].

Neonatal hyperphenylalaninemia is caused by a defect in phenylalanine metabolism. Two situations have recently emerged : patients with a phenylalanine-hydroxylase deficiency and patients with a defect in de novo synthesis of the cofactor tetrahydrobiopterin. These two categories can be distinguished by enzyme assays and assessment of the levels of pteridines in urine. Because of the need for different treatments, an early differential diagnosis of these forms is crucial. Concerning the study of 18 newly screened hyperphenylalaninemic babies, we have discussed the methods of diagnosis : liver biopsy for enzymatic determinations appeared as too invasive a method; in contrast, the quantitative analysis of pteridines in urine permitted a rapid discrimination of the variants.