Fig. 5

Algorithm of BH4 loading test for children after neonatal period and aged < 4 years. The BH4 loading test must be performed in relation to the genotype (the presence of only one responsive mutation or of one mutation of unknown responsiveness). When the genotype is unknown, the BH4 loading test should be performed, if available. BH4: Tetrahydrobiopterin; Phe: Phenylalanine; PKU: Phenylketonuria