Diagnostic and therapeutic recommendations for the treatment of hyperphenylalaninemia in patients 0–4 years of age

Ania C. Muntau, Marcel du Moulin, Francois Feillet

Treatment of phenylketonuria (PKU) with sapropterin dihydrochloride in responsive patients from an early age can have many advantages for the patient over dietary restriction alone. Accordingly, approval of sapropterin in the European Union was extended in 2015 to include patients aged 0-4 years, bringing the treatment age range in line with that in the USA and providing an additional treatment option for those patients with PKU who are responsive or partially responsive to treatment with sapropterin. Subsequently, European guidelines have been published on the diagnosis and management of patients with PKU. However, testing for PKU can be demanding and requires particular expertise. We have compiled experience-based, real-world guidance in an algorithmic format to complement the published guidelines, with the overall aim to achieve optimized and individualized care for patients with PKU. Our guidance covers aspects such as how to perform, monitor and interpret appropriate biochemical measures to achieve effective patient management and desired outcomes, how to perform a tetrahydrobiopterin (BH4) loading test to assess responsiveness in newborns, and how to initiate sapropterin treatment in patients from birth. We also provide our expert opinion on starting pharmacotherapy in patients who were previously managed by diet alone. Real-world-based guidance is particularly important in managing therapeutic strategies in newborns with PKU to achieve optimal long-term outcomes and will serve as a complement to the other published guidelines.