Predictors of mean phenylalanine levels during the first five years of life in patients with phenylketonuria who were treated early. Dutch National PKU Steering Committee.

We studied the relationship between plasma phenylalanine level at first diagnostic visit, country of origin of the mother, birth cohort, child clinic, sex, and social class on the one hand and mean plasma phenylalanine levels in the first five years of life on the other hand in patients with phenylketonuria (PKU) who were treated early. The study population consisted of 131 early treated patients with PKU born during the period from September 1st, 1974 to December 31st, 1988 in The Netherlands. Plasma phenylalanine levels from first diagnostic visit (usually before the age of three weeks) up until the fifth birthday were registered. For each patient the mean phenylalanine level during that period was calculated. Our results suggest that 1) it is more difficult to maintain low phenylalanine levels in patients with a more severe form of PKU, 2) in recent years paediatricians have treated their patients with a stricter diet, 3) there are differences in perception between paediatricians of different clinics as to what levels are acceptable, and 4) treatment of patients from non-Dutch mothers is more difficult than treatment of patients with Dutch mothers.