Influence of knowledge of the disease on metabolic control in phenylketonuria.

Abstract

In patients with phenylketonuria (PKU) knowledge of the disease and its treatment is not a major independent predictor for dietary compliance. PKU is an inborn error of amino-acid metabolism caused by a deficiency of phenylalanine hydroxylase (PAH), resulting in high plasma phenylalanine (Phe) concentrations and consequently severe mental retardation. Treatment comprises a life-long diet and PKU patients maintaining good metabolic control develop normally [3]. Poor dietary compliance is a regularly encountered problem. Increasing knowledge of the disease and its treatment may be a possibility to improve dietary compliance. Until now few studies have investigated this issue in PKU and the results are not conclusive [2, 4, 5, 6]. We therefore conducted a study to assess knowledge of the disease and its treatment in a large population of PKU patients and their parents and to determine the association between knowledge and the plasma Phe concentration as an indicator of dietary compliance in PKU. Parents of 161 PKU patients (aged 1 to 22 years) and 62 PKU patients (aged 12 to 22 years) completed a questionnaire to assess knowledge. The mean plasma Phe concentration during a 3-year period (1994 to 1996) was taken as an indicator of metabolic control. Table 1 shows the questions and the number of parents and patients correctly answering each separate question. We had expected that the greater part of the patients and their parents would correctly answer the questions. However, only 52% of the parents and 29% of the patients answered more than 11 of the 14 questions adequately. Linear regression showed that higher knowledge was associated with lower Phe concentrations, but this association was statistically significant only in the parent group (parents: b=)28, 95% CI)39/)17; patients: b=)20, 95% CI)42/2). After adjustment for confounders (pre-treatment Phe concentrations and dietary Phe tolerance, both as indicators for the severity of the enzyme deficiency, patient’s age, parental educational level and ethnicity) this association disappeared (parents: b=)0.4, 95% CI)8/ 7; patients: b=)1.5, 95% CI)10/7) and pre-treatment Phe concentrations, Phe tolerance and ethnicity were the strongest predictors for Phe concentration.