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Phenylalanine requirement in children with classical PKU determined by indicator amino acid oxidation
Glenda Courtney-Martin1, Rachelle Bross, Mahroukh Raffi
1Department of Nutritional Sciences, University of Toronto, Toronto M5S 3E2, Canada.
Insights
Phenylalanine requirements for phenylketonuria (PKU) patients were precisely determined using indicator amino acid oxidation. The study suggests a maximal phenylalanine intake of 20 mg/kg/day for children with PKU.
Area of Science:
- Metabolic disorders
- Nutritional biochemistry
- Medical biochemistry
Background:
- Phenylketonuria (PKU) management relies on dietary phenylalanine restriction.
- Current phenylalanine requirement estimates are based on plasma levels and growth, lacking precision.
Purpose of the Study:
- To precisely determine phenylalanine requirements in PKU patients.
- To establish a safe upper intake level for phenylalanine in PKU management.
- To refine dietary guidelines for PKU treatment.
Main Methods:
- Utilized indicator amino acid oxidation with L-[1-13C]lysine to measure phenylalanine requirements.
- Employed breath 13CO2 production (F 13 CO2) as the endpoint for oxidation.
- Collected finger-prick blood samples to correlate phenylalanine intake with plasma levels.
Main Results:
- The mean phenylalanine requirement was estimated at 14 mg/kg/day.
- The safe population intake (upper 95% CI) was determined to be 19.5 mg/kg/day.
- A balance between intake and blood levels was observed at 20 mg/kg/day, suggesting this as a maximal intake.
Conclusions:
- The precise phenylalanine requirement for PKU patients is 14 mg/kg/day.
- A safe upper intake limit for the PKU population is 19.5 mg/kg/day.
- Maximal phenylalanine intake for children with PKU should not exceed 20 mg/kg/day.
Abstract:
Dietary restriction of phenylalanine is the main treatment for phenylketonuria (PKU), and current estimates of requirements are based on plasma phenylalanine concentration and growth. The present study aimed to determine more precisely the phenylalanine requirements in patients with the disease by use of indicator amino acid oxidation, with L-[1-13C]lysine as the indicator. Breath 13CO2 production (F 13 CO2) was used as the end point. Finger-prick blood samples were also collected for measurement of phenylalanine to relate phenylalanine intake to blood phenylalanine levels. The mean phenylalanine requirement, estimated using a two-phase linear regression crossover analysis, was 14 mg. kg(-1). day(-1), and the safe population intake (upper 95% confidence interval of the mean) was found to be 19.5 mg. kg(-1). day(-1). A balance between phenylalanine intake and the difference between fed and fasted blood phenylalanine concentration was observed at an intake of 20 mg. kg(-1). day(-1). The similarity between these two values (19.5 and 20 mg. kg(-1). day(-1)) suggests that the maximal phenylalanine intake for children with PKU should be no higher than 20 mg. kg(-1). day(-1).