The effect of slow releasing carbohydrates on the variability of plasma amino acid concentrations in PKU-patients in childhood.

Metabolic control in PKU is based on regular blood sampling to measure plasma
Phe concentration. The intake of Phe is adjusted when plasma Phe concentrations
are not within the target range, taking into account other factors that
influence metabolic control: e.g. intercurrent infections, growth, energy
intake and amino acid supplementation. Studies on the diurnal variation of
plasma Phe concentrations, showed an inverse pattern when compared with
healthy controls: in PKU patients Phe concentrations measured after an
overnight fast are the highest, and decrease during the day. A hypothesis for
the rise in blood Phe concentration overnight is the occurrence of catabolism
during the fasting period resulting in a higher amount of Phe available than
the amount used for protein synthesis.

A reduction of the fasting period may prevent or reduce the rise in plasma Phe
concentration. Therefore, the aim of the study is to measure the effect of the
application of slow releasing carbohydrates (SRC) as evening meal before
bedtime on the overnight fasting blood Phe concentration in comparison to fast
releasing carbohydrates (FRC).

This pilot study has a randomized double-blind cross-over design

Addition of SRC or FRC to the 3d portion of amino-acid supplementation at
bedtime: the additional carbohydrates will be diluted in the fluid amino acid
supplement with some extra water. When the amino acid supplement is not taken
as a fluid, the additional carbohydrates will be solved in water and (optional)
flavouring (flavor sachets Vitaflo).

Extra risico's ten opzichte van de gebruikelijke behandeling worden bij de
studie niet verwacht. De extra inname van koolhydraten kan de uitgesproken
smaak van de gebruikelijke aminozuren wel enigszins beinvloeden en zal ook het
volume van deze suppletie vergroten, maar de verwachting is dat dit geen grote
problemen zal geven.
Participating the study includes during 2 periods of 8 days:
- twice daily a fingerpuncture, daily report of stool and body weight
- during 2 of the 8-days period food record registration
- taking the individual diet as usual for the patient with exception of the
third portion amino acid supplementation, to which ad bedtime in the
intervention period slow and fast releasing carbohydrates will be added conform
the study protocol.
The study will be performed at home, and the extra effort of the participants
concerns mainly the higher frequency of bloodsampling with a fingerpuncture.
Risks associated with the study are not to be expected. May be the extra intake
of carbohydrates will influence the taste and volume of the amino acid mixture
but is not expected as problematic as the mixture itself has a very pronounced
taste.