Prenatal diagnosis in primary hyperphenylalaninemias.

Prenatal diagnosis can be made in primary hyperphenylalaninemia due to either phenylalanine hydroxylase or tetrahydrobiopterin deficiency. First or second trimester diagnosis is possible, depending on the type of inherited disorder and on the availability of reliable methods. Seven prenatal diagnoses were performed: four in couples at risk for 6-pyruvoyl tetrahydropterin synthase deficiency, two in couples at risk for dihydropteridine reductase deficiency, and one in a couple at risk for phenylketonuria. The reliability of different procedures and analyses was examined. The measurement of pterins in amniotic fluid and/or of the specific enzyme activity in fetal erythrocytes and amniocytes allows to avoid the risk for all types of tetrahydrobiopterin deficiency, whereas in phenylketonuria prenatal diagnosis relies on molecular analysis by recombinant DNA techniques.