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Updated: Aug 20, 2026

In Vitro Enzyme Measurement to Test Pharmacological Chaperone Responsiveness in Fabry and Pompe Disease
Published on: December 20, 2017
Tetrahydrobiopterin responsiveness in patients with phenylketonuria
Belén Pérez-Dueñas1, Maria Antonia Vilaseca, Anna Mas
1Department of Neuropediatrics, Hospital Sant Joan de Déu, Universitat de Barcelona, Barcelona, Spain.
Objectives:
To investigate the BH4 response in a group of patients with phenylketonuria (PKU) in order to offer this alternative treatment to the responsive patients.
Design And Methods:
The 24-h-long Phe/BH4 loading test was performed on 64 PKU patients requiring dietary treatment.
Results:
All patients with mild-PKU and 75% of patients with moderate-PKU were BH4 responsive, while only 11% of classic-PKU patients showed good/partial response (P < 0.0001). The percentages of Phe decrease after the BH4 loading test were significantly different in the three PKU phenotypes (mild PKU: 67.9 +/- 18.7; moderate PKU: 37.4 +/- 16.8; and classical PKU: 21.9 +/- 13.7; ANOVA with Bonferroni correction: P < 0.0001). We report four mutations (P147S, D222G, P275S, and P362T) not previously associated with BH4 responsiveness, all of them combined with mutations with zero predicted residual activity.
Conclusion:
Both the percentage of Phe decrease and the Phe value achieved 24 h after BH4 loading are valuable data in predicting a response. We report four mutations not previously associated with BH4 responsiveness.
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