Factors affecting the success of follow-up and treatment of adults with phenylketonuria diagnosed by newborn screening

OBJECTIVES: Phenylketonuria (PKU) is an autosomal recessive metabolic disorder caused by phenylalanine hydroxylase deficiency, leading to elevated phenylalanine (Phe) levels in blood and brain. Lifelong dietary treatment is required to prevent neurotoxicity, yet adherence often declines during adulthood. This study aimed to evaluate follow-up and treatment adherence in adults with PKU and to explore strategies to improve long-term metabolic control. METHODS: This cross-sectional study included adult PKU patients followed at the Division of Pediatric Nutrition and Metabolism, Istanbul Medical Faculty. Data were collected between April and July 2021 using retrospective medical records and online questionnaires. Follow-up and treatment success rates were assessed according to blood Phe monitoring frequency and results within the target range. Participants completed the Adult Attention Deficit Hyperactivity Disorder Self-Report Scale and the Phenylketonuria Quality of Life Questionnaire. RESULTS: Data were collected from 134 of the 198 registered patients. The average age was 23.25 ± 2.92 years, and 50 % were female. Classical PKU was present in 68.7 %. Patients with classical PKU demonstrated higher follow-up success than those with mild PKU. Individuals who self-managed their diet showed significantly higher follow-up and treatment success. No significant associations were observed between success rates and age at diagnosis, residence, working status, family education, or ADHD scores. A significant negative correlation was found between success rates and quality-of-life subdomains related to dietary management and daily life burden. CONCLUSIONS: Treatment success in adults with PKU may be improved by promoting dietary self-management, increasing awareness of treatment options, facilitating dietary implementation, and reducing disease-related burden. This study demonstrates that in adults with phenylketonuria, follow-up and treatment success are primarily influenced by disease severity and patients' ability to self-manage their diet, highlighting the need for strategies that reduce daily disease burden and support long-term dietary adherence.