Efficiency of long‐term tetrahydrobiopterin monotherapy in phenylketonuria

Abstract Summary: Phenylketonuria, an inborn error of phenylalanine metabolism, occurs with a frequency of about 1 in 10 000 births and is treated with a strict dietary regimen. Recently, some patients with PKU have been found to show increased tolerance towards phenylalanine intake while receiving tetrahydrobiopterin (BH 4 ) supplementation. We have treated two infants with BH 4 ‐responsive PKU with BH 4 for more than 2 years. No additional dietary control was required to maintain blood phenylalanine concentrations in the desired range. Both children have shown normal development. Generally, our results suggest that BH 4 treatment might be an option for some patients with mild PKU, as it frees them from dietary restrictions and thus improves their quality of life.