These guidelines for nutritional management and monitoring of PKU treatment are based on the best available evidence as well as survey results and expert opinion. In nearly all areas collection of more clinical data, well-designed clinical trials, and use of patient registries have potential to increase the validity of the recommendations. In addition, future research will be able to evaluate areas now being investigated, such as: 

• Development of new therapies (hepatocyte transplantation)
• Quantification of brain concentrations of amino acids, especially PHE and other large neutral amino acids, and their relation to dietary intake and cognitive outcome
• Elucidation of the mechanism of osteoporosis in PKU
• Benefits and/or harms associated with use of glycomacropeptide as the protein source in PKU medical foods
• Role of oxidative stress and/or potential renal acid load in the pathophysiology of PKU-related symptomatology
• Impact of PKU on the gut microbiome
• Impact of blood hypoPHE and/or hypoTYR 
• Effect on nutritional status associated with normalized dietary intake when allowed by alternate therapies (pegvaliase) 
• Safety of pegvaliase therapy in pregnancy and lactation.