Therapy compliance in children with phenylketonuria younger than 5 years: A cohort study

Phenylketonuria (PKU) is a metabolic disease. It is manifested by a complete or partial inability to convert phenylalanine (Phe) to tyrosine and leads to increased concentrations of Phe in the blood and in other tissues, including the brain, causing irreversible neurological damage if left untreated. Low-phenylalanine diet is a key component of classical PKU therapy. The objective of this study was to assess the effectiveness of classical phenylketonuria therapy and compliance with doctors' recommendations in the first 5 years of life. Data was collected from all diagnosed and treated patients (n = 57) born 1999-2010. Phenylalanine blood levels, the number of visits to a specialist outpatients' center, the number of blood tests, as well as socioeconomic status (SES) and parents' education level have been analyzed, and potential relationships have been assessed. In the 1st year of life patients visited their doctors (OR = 6.8267; 95% CI = 2.827-16.5163; p < 0.0001) and had their blood collected (OR = 2.7875; 95% CI = 1.0467-7.4234; p < 0.0402) significantly more frequently than in the 2nd year. This tendency persisted into subsequent years. Similarly, in infancy they had statistically significantly lower odds of exceeding more than 40% of their Phe levels over therapeutic range than 1 year later (OR = 3.6078; 95% CI = 1.4859-8.7599; p < 0.0046). No PKU child had more than 70% of Phe levels over the therapeutic range in the 1st year of life, whereas 4 years later there were 18 such children. Phe levels were correlated with the number of visits to a specialist (ρ = 0.39) and the number of Phe blood tests with index of dietary control (ρ = -0.33). The effectiveness of therapy and compliance with the doctor's recommendations seem to depend neither on the level of education of the patient's parents nor on their SES. Therapy effectiveness and patients' compliance in PKU is very good in infancy. However, both deteriorate in subsequent years. Moreover, they do not seem to depend on the family background.