Behavioural factors related to metabolic control in patients with phenylketonuria

Background. The objective of this study was to determine the importance of parental factors possibly related to dietary control in early and continuously treated patients with phenylketonuria (PKU). Methods. A questionnaire was disseminated among parents of 238 patients with PKU born after the nationwide introduction of newborn screening for PKU (1 September 1974) until 31 December 1995. The questionnaire was based on a behavioural model measuring people's attitudes, subjective norms, and self-efficacy. Dietary control was defined on the basis of mean phenyl- alanine (Phe) concentration of the PKU patients measured between 1 January 1994 and 31 December 1996. Results. Response rate was 71%. Attitudes: children of parents who believed that their child adheres well to the diet, even if his or her Phe concentrations are sometimes too high, had lower Phe concentrations than children of parents who disagree with this statement (adjusted difference -103 mu mol/L, p <0.001). Subjective norm: Phe concentrations were higher when parents answered that their relatives did not approve when their child deviates from the diet (p = 0.004). Self-efficacy: children of parents who reported difficulties in having their child eat the synthetic protein substitute three times a day had higher Phe concentrations than those of parents who did not have such difficulties (adjusted difference 156 mu mol/L, p = 0.007). Conclusion. More attention should be given to parents having their child eat the synthetic protein substitute at least three times a day and to teaching parents to keep strictly to the diet without being too rigid. These factors were strongly associated to dietary control and may be amenable to change.