Diurnal variations in blood phenylalanine of PKU infants under different feeding regimes

In phenylketonuria (PKU) patients, diurnal fluctuations of blood phenylalanine (Phe) are different from healthy individuals. Until now this pattern has been studied in PKU patients over one year of age.ObjectiveThe aim of this observational study was to investigate diurnal patterns in PKU infants under one year of age receiving both the natural protein and Phe-free formula at the same time or in an alternating feeding scheme.MethodsIn 7 PKU infants (aged 3–8 months), diurnal variations in blood Phe concentrations were recorded: on day A they received natural protein and Phe-free formula combined in each feeding; on day B they received these in an alternating feeding scheme. The number of feedings, total protein, and energy intake was similar on both study days. Blood samples were taken before each feeding.ResultsThe means (± SD) of the difference between the individual minimum and maximum blood Phe concentrations were 81(± 50) μmol/L and 104(± 26) μmol/L on days A and B, respectively (n.s.). Fifty and 30% of the samples were below target range for age (120 μmol/L), while only 3% and 6% were above target range (360 μmol/L) on days A and B respectively (n.s.).ConclusionBoth feeding regimes, i.e. the natural protein and Phe-free formula combined in each feeding or alternating, resulted in comparable diurnal fluctuations of blood Phe concentrations.

► Unequal Phe distributions do not change diurnal variation of blood Phe concentration.
► Different breastfeeding regimes do not disturb metabolic control and growth.
► Low blood Phe concentrations deserve the same attention as high concentrations.