Radha Ramachandran, Katrin Õunap, Maja Stojiljkovic, Neslihan Önenli Mungan, Callum Wilson, Clara D.M. van Karnebeek, Vincenzo Leuzzi, Nenad Blau, Gwendolyn Gramer, Kimberly K. Powell, William B. Hanley, Carla E. M. Hollak, Miroslaw Bik-Multanowski, F. K. Trefz, Maja Djordjevic, K. Ahring, Jozef Hertecant, Fatma Derya Bulut, François Feillet, Annemiek M. J. van Wegberg, Danique van Vliet, Natalia Usurelu, Bozena Didycz, Kari Casas, Frank Rutsch, Jens V. Jørgensen, Maria Gizewska, Antonio Federico, Aria Setoodeh, Kathryn Moseley, Francesca Nardecchia, Francjan J. van Spronsen, Yuval Landau, Per Mathisen, Daniela Karall, University of Zurich, van Spronsen, Francjan J, Çukurova Üniversitesi, Endocrinology, AGEM - Inborn errors of metabolism, ANS - Cellular & Molecular Mechanisms, and Paediatric Metabolic Diseases
Background Phenylketonuria (PKU) is often considered as the classical example of a genetic disorder in which severe symptoms can nowadays successfully be prevented by early diagnosis and treatment. In contrast, untreated or late-treated PKU is known to result in severe intellectual disability, seizures, and behavioral disturbances. Rarely, however, untreated or late-diagnosed PKU patients with high plasma phenylalanine concentrations have been reported to escape from intellectual disability. The present study aimed to review published cases of such PKU patients. Methods To this purpose, we conducted a literature search in PubMed and EMBASE up to 8th of September 2017 to identify cases with 1) PKU diagnosis and start of treatment after 7 years of age; 2) untreated plasma phenylalanine concentrations ≥1200 μmol/l; and 3) IQ ≥80. Literature search, checking reference lists, selection of articles, and extraction of data were performed by two independent researchers. Results In total, we identified 59 published cases of patients with late-diagnosed PKU and unexpected favorable outcome who met the inclusion criteria. Although all investigated patients had intellectual functioning within the normal range, at least 19 showed other neurological, psychological, and/or behavioral symptoms. Conclusions Based on the present findings, the classical symptomatology of untreated or late-treated PKU may need to be rewritten, not only in the sense that intellectual dysfunction is not obligatory, but also in the sense that intellectual functioning does not (re)present the full picture of brain damage due to high plasma phenylalanine concentrations. Further identification of such patients and additional analyses are necessary to better understand these differences between PKU patients. Electronic supplementary material The online version of this article (10.1186/s13023-018-0890-7) contains supplementary material, which is available to authorized users.