A pioneering transition program for adults with phenylketonuria - initial findings from a single-center one-year experience from Poland.

Background In August 2024, at the University Hospital in Krakow, we initiated, for the first time in Poland, the transition of individuals with hyperphenylalaninemia to the adult metabolic center. We evaluated the experience and outcomes during the first year of this transition program. Methods We included 120 adults with hyperphenylalaninemia who were followed between August 1st, 2024, and July 31st, 2025, in the Outpatient Metabolic Clinic at the University Hospital in Krakow, Poland. Results The mean age of individuals was 31.77±10.80 years (range 18‒68); 69 (57.5%) were females. The majority, 101 (84.2%), were individuals with classic Phenylketonuria (PKU). Twenty (17.7%) individuals were off-diet, and a further 38 (33.6%) reported poor adherence. Participants were followed for a median of 5.6 (3.5‒7.7) months. The mean DBS Phe concentration from the 5-year period preceding the transition was 717.00±350.40 µmoL/L, with a mean percentage of results > 600 µmoL/L of 57.0 ± 41.4%. The mean Phe concentration during the follow-up period was 689.40±373.20 µmoL/L, with 55.5 ± 44.2% of Phe measurements exceeding the target value of 600 µmoL/L, revealing no significant change (p = 0.868 and 0.754, respectively). Seven (26.9%) children of transitioned individuals showed symptoms of maternal PKU. Conclusions The initially poor Phe control in the cohort studied remained unchanged after transferring to the adult center, emphasizing that maintaining a restrictive diet in adults with PKU is challenging. Alarmingly high prevalence of unplanned pregnancies and maternal PKU highlights critical reproductive health concerns in this population. A longer follow-up is needed to assess the impact of the transition on the metabolic control of Phe.