From: Diagnostic and therapeutic recommendations for the treatment of hyperphenylalaninemia in patients 0–4 years of age
• Two null mutations in trans: no reason to perform further tests on the responsiveness to BH4; treat with Phe-restricted diet.
• Two responsive mutations: treat the patient with sapropterin.
• One responsive mutation or unknown genotype: consider further tests for BH4 responsiveness.
• If the genotype is not identified, further tests of BH4 responsiveness should be considered.