Cognitive functions in patients with phenylketonuria in long-term treatment with tetrahydrobiopterin

Abstract Cognitive functions were assessed in 9 patients with mild to moderate phenylketonuria (PKU) ranging from 6 to 18 years of age, who were in long-term treatment (>5 years) with 5–9 mg/kg/day tetrahydrobiopterin (BH4) on compassionate use, provided by Schircks Inc. An extensive study of cognitive functions (intelligence quotient (IQ), visuospatial, visual memory, fine motor, executive and attentional functions) was conducted, and behavior was assessed using the ADHD Rating Scale and the Behavior Rating Inventory of Executive Function (BRIEF). All patients had normal IQ ( M  = 107, SD = 10). The most notable area of impairment was fine motor function, but no significant difference was found between the PKU patients in BH4 treatment who participated in the current study and PKU patients in dietary treatment who participated in a previous study. These results, however, should be interpreted with caution. It is necessary to conduct further studies with a larger number of patients, using more sensitive tests of motor function and using the formulation of BH4 that is currently available.