Navigating Adolescence with PKU: Adherence, Metabolic Control, and Wellbeing in a UK Clinical Centre

Background: During adolescence, the brain is undergoing anatomical and physiological maturation processes with changes to cognitive development. However, in adolescents with phenylketonuria (PKU), executive function and mental health are adversely affected by high blood phenylalanine (Phe) levels. Objectives: We aim to describe clinical outcomes in adolescents with PKU. Methods: Cross-sectional questionnaires were performed on quality of life (EuroQol “EQ-5D-5L” questionnaire), anxiety and depression (Hospital Anxiety and Depression Scale- HADS) and food neophobia in a single PKU centre. Retrospective data on metabolic control (previous 12 months) and medical history, and current data on anthropometry, dietary treatment, and comorbidities were collected. Results: In total, 33 adolescents with PKU participated with a mean age of 13.5 ± 1.3 y (16 boys, 17 girls). All were on a Phe restricted diet, with 3 also prescribed sapropterin. Questionnaires were self-completed by n = 25/33 (76%) adolescents. A mean of 36 ± 26 blood Phe spots were performed over 12 months. There was a mean of 83% of blood Phe < 600 µmol/L and 49% < 360 µmol/L. In total, 39% (n = 13/33) of adolescents were overweight/obese, 18% (n = 6/33) overweight and 21% (n = 7/33) obese. Medical history documented mental health disorders (anxiety/depression) in 7 cases, low mood, suicidal thoughts and self-harming in 5, and neuro diversity in 4 (autism and/or attention-deficit hyperactivity disorder (ADHD). In the HADS questionnaire, 12% (n = 3/25) of adolescents scored borderline abnormal for anxiety and 12% (n = 3/25) abnormal for depression. Mean anxiety scores for females were almost twice as high compared to males. No significant correlation was found between blood Phe and anxiety/depression scores. However, higher Phe levels showed a trend towards reduced enjoyment and emotional responsiveness, including lower scores on measures of pleasure, cheerfulness, and emotional reactivity. Although not statistically significant, these findings suggest a potential subtle association between poorer metabolic control and mood disturbances in adolescents with PKU. No food neophobia was identified in our study. Conclusions: Adolescents with PKU presented with high levels of depression and anxiety. Long term studies focusing on quality of life and neurocognition even when achieving the PKU European guidelines are necessary. Different therapeutic options are needed to improve the outcome of patients with PKU.