Phenylketonuria (PKU) is a rare genetic disorder in which the amino acid phenylalanine cannot be sufficiently metabolised. Although a build-up of phenylalanine causes irreversible cognitive impairment, this can be prevented through a strict, lifelong diet restricted in natural protein. Despite the severe consequences of poor metabolic control, many children and adolescents have phenylalanine levels above their recommended limits. This systematic review was the first to examine studies reporting demographic and/or psychosocial influences on blood phenylalanine levels, with the aim to identify factors that were robustly linked with metabolic control. Four electronic databases were searched, yielding 1,808 articles. Articles were included if they reported a statistical examination of the association between one or more demographic or psychosocial factor(s) and metabolic control (as measured by blood phenylalanine concentration) for children and adolescents with PKU. Twenty-nine studies were selected for inclusion, which examined a range of child, parent and family factors related to blood phenylalanine levels. The most reproducible association was with child age, with metabolic control worsening with increasing age. This suggests that interventions promoting treatment adherence would be particularly beneficial for adolescents. There was a paucity of studies in some areas, and the quality of included studies varied; therefore, the conclusions of this review are preliminary. Research recommendations focus on promoting the growth of the evidence-base to support clinical practice.
Keywords: Adherence; Children; Demographic; Metabolic; Phenylketonuria; Psychosocial.