Phenylalanine supplementation in Tyrosinemia type 1

Rationale:Hereditary Tyrosinemia Type 1 (HT1) patients usually present with liver dysfunction and or renal tubular dysfunction with rickets early in life. After the introduction of 2-(2-nitro-4-trifluoro-methylbenzoyl)-1,3-cyclohexanedione (NTBC), problems resolved and life expectancy greatly increased. However, due to NTBC, which blocks the conversion of tyrosine at an earlier step, tyrosine concentrations increase, making dietary restrictment of tyrosine and its precursor phenylalanine necessary. Recently, some articles report low phenylalanine concentrations in HT1, making phenylalanine supplementation necessary despite possible conversion to tyrosine and resulting increase in tyrosine. Next to that, previous research of us showed a strong diurnal variation of phenylalanine, with extremely low phenylalanine concentrations early in the afternoon. These strong diurnal variation and increase in tyrosine concentrations make more studies on the optimal dose of phenylalanine supplementation necessary.

Objective: The main objective of this study is to investigate the effect of phenylalanine supplementation on phenylalanine and tyrosine concentrations.

Study population: We estimate that 15 HT1 patients will be included in this study all treated with NTBC, a tyrosine and phenylalanine restricted diet and phenylalanine suppletion.

Main study parameters: phenylalanine, tyrosine, NTBC and succinylacetone concentrations during the day at different doses of phenylalanine supplementation in HT1 patients.

Study design: Patients will be treated with 2 different amounts of phenylalanine supplementation. The participating HT1 patients will perform 2 rounds of 13 bloodspots (taken by finger prick). Next to this 8 bloodspots are done to set a baseline without supplementation. The total duration of the study is 24 days.

Phenylalanine supplementation can result in higher phenylalanine concentrations without causes tyrosine concentrations to rise too much

Patients from the University Medical Center Groningen, the Netherlands will be included first. Afterwards, patients from the Birmingham Children's Hospital, UK will be included in this study.

Different doses of phenylalanine supplementation will be given during some days. The effect of the supplementation on metabolic control will be studied while receiving the different dosages.