Therapy with Sapropterin Dihydrochloride (6R-BH4) in a Patient with Phenylketonuria

A patient with phenylketonuria who may benefit from saptropterin therapy should show at least a 20% reduction in phenylalanine levels during a trial with controlled phenylalanine intake. The START protocol of Utz et al is one such protocol.

The response to sapropterin is dose-dependent, with response higher at doses of 20 mg/kg per day than at lower dosages.

Certain genotypes are more likely to be responsive and other genotypes less responsive. Utz et al indicate that a genotype with at least one allele with >= 25% residual activity compared to the wild type is likely to respond to saptropterin.

For example, all patients with p.Y414C were responsive to sapropterin while p.R408W was associated with nonresponse.

Sapropterin therapy is continued in patients who demonstrate a benefit from its use.