Short term changes in plasma phenylalanine status and cognitive processing speed in adolescent and adult females with phenylketonuria (PKU)

Abstract

Even with early and continuous diet therapy, subtle neuropsychological deficits exist in phenylketonuria (PKU). To clarify the relationship between compliance and processing speed, this study examines the relationship between short‐term changes in plasma phenylalanine (Phe) concentration and cognitive processing speed. Data were collected from twenty females with PKU (ages 12‐47 years) attending a summer camp intervention designed in part to reduce plasma Phe. Pre‐ and post‐intervention fasting plasma Phe was assessed using ion‐exchange chromatography. Pre‐ and post‐intervention processing speed was assessed in group format by Woodcock‐Johnson III timed tests of decision speed and pair cancellation. As expected, mean plasma Phe and processing speed scores significantly improved (p<0.001) and pair cancellation negatively correlated with change in plasma Phe controlling for verbal ability (r=‐0.627, p=0.004). Changes in decision speed and plasma Phe, however, were unrelated. Pair cancellation may be more sensitive to improved Phe control due to the task's reliance on attention and concentration. Short‐term improved compliance may be associated with concurrent improved processing speed. Supported in part by PHS Grant M01 RR00039 from the General Clinical Research Center program, National Institutes of Health, National Center for Research Resources.