Effects of concurrent phenylalanine levels on sustained attention and calculation speed in patients treated early for phenylketonuria.

The effects of short-term and long-term phenylalanine (Phe) levels on sustained attention have been investigated in phenylketonuria (PKU) patients. Two studies, one cross-sectional with 103 patients aged 8.5-9.0 years, the other with 15 adult patients following an interventional design with experimentally manipulated concurrent Phe levels are reported. The effects of concurrent Phe levels separated from long-term Phe control on sustained attention and calculation speed in simple addition tasks were investigated. Children with low concurrent Phe levels performed significantly better than children with high concurrent Phe levels when long-term dietary control was good but not when long-term control was poor. Adult PKU patients with high concurrent Phe levels showed significantly longer reaction times and lower speed in calculation than a healthy control group. Deficits were partly reversible by lowering the concurrent Phe level over a period of 4-5 weeks. The results demonstrated the impact of concurrent Phe level on neuropsychological functioning in childhood as well as in adulthood.