[Differential diagnosis of increased phenylalanine blood level in infancy. Results of the German collaborative study on phenylketonuria (PKU)/hyperphenylalaninemia (HPA)].

Between 1978 and 1984 165 children with elevated Phe blood levels in newborn screening were included in a German multicentric study. The differential diagnosis, comprising Phe concentrations in the blood under a tetrahydrobiopterin (BH4) load (30 mg BH4), determination of pterins in the urine and dihydropteridin reductase (DHPR) in erythrocytes, resulted in two patients with a 6-pyruvoyltetrahydrobiopterin synthase (PTPS) deficiency. Those patients with a defect in the apoenzyme phenylalanine hydroxylase (PH) were treated with a low Phe diet, when the Phe blood concentrations exceeded 10 mg/dl under an adapted formula (n = 154). At the age of six months, in 155 infants a protein challenge containing 180 mg Phe/kg body weight for three days was performed, followed by a fourth day with 5 mg Phe/kg. Corresponding to the US Collaborative Study [19] 3 types of response were chosen according to the course of the Phe blood level under the challenge (n = 145). Type I response (n = 112) shows a continuous increase of the Phe more than 20 mg/dl even under the Phe restriction at day 4. Type II response (n = 14) shows also increasing Phe blood levels above 20 mg/dl, followed by a spontaneous decrease below 20 mg/dl still during the high Phe challenge and even lower at the fourth day with low Phe intake. Type III response (n = 19) had only a small increase of the Phe blood concentration, mostly below 15 mg/dl during the whole challenge period.(ABSTRACT TRUNCATED AT 250 WORDS)