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Vision science
Communication
Retinal nerve fibre layer thickness associates with phenylketonuria control and cognition
  1. Jan Krzysztof Nowak1,
  2. Łukasz Kałużny1,
  3. Wojciech Suda2,
  4. Anna Bukowska-Posadzy1,3,
  5. Alex Adams4,
  6. Ireneusz Grulkowski5,
  7. Jarosław Kocięcki2,
  8. Jarosław Walkowiak1
  1. 1Department of Pediatric Gastroenterology and Metabolic Diseases, Poznan University of Medical Sciences, Poznan, Poland
  2. 2Department of Ophthalmology, Poznan University of Medical Sciences, Poznan, Wielkopolskie, Poland
  3. 3Department of Clinical Psychology, Poznan University of Medical Sciences, Poznan, Wielkopolskie, Poland
  4. 4Translational Gastroenterology Unit, Nuffield Department of Clinical Medicine, Division of Experimental Medicine, University of Oxford, Oxford, Oxfordshire, UK
  5. 5Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Torun, Torun, Poland
  1. Correspondence to Dr Jan Krzysztof Nowak, Department of Pediatric Gastroenterology and Metabolic Diseases, Poznan University of Medical Sciences, 61-701 Poznan, Poland; jan.nowak{at}ump.edu.pl

https://doi.org/10.1136/jmedgenet-2019-106770

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    Phenylketonuria (PKU) is efficaciously treated by low-phenylalanine (Phe) diet but the views on the acceptable range of Phe constantly evolve. In 1997, German guidelines allowed Phe concentrations of up to 20 mg/dL (1200 µmol/L) in adults.1 Currently, American and European recommendations are discordant, promoting Phe levels below 6 and 10 mg/dL (360 and 600 µmol/L) from adolescence onwards, respectively.2 3 There are insufficient data to prefer one over the other recommendation, which reduces patient motivation, and the objective tools to resolve the dispute or elucidate unexplored vulnerability factors are scarce.4 5 An easily interpretable, accessible and non-invasive biomarker of neural damage in PKU is lacking. We demonstrate that retinal nerve fibre layer (RNFL) thickness measured using optical coherence tomography (OCT) may associate with PKU control and cognition.

    This observational study enrolled 15 patients with classical PKU diagnosed through newborn screening and aged 15.2±5.2 years (mean±SD; 5 men and 10 women). All patients gave informed written consent for their participation in the study. All the participants underwent a standard eye examination, which was unremarkable, followed by retinal OCT scanning (DRI OCT Triton, Topcon, Tokyo, Japan). The peripapillary RNFL thickness in four sectors (nasal, inferior, temporal and superior) was extracted from the acquired three-dimensional OCT datasets using built-in software of the instrument. Psychological assessment was conducted using the Wechsler Adult Intelligence Scale or the revised Wechsler Intelligence Scale for Children by one practitioner (ABP) who has been providing care to the …

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    Footnotes

    • Contributors JKN conceptualised and designed the study, collected and analysed the data, and drafted the manuscript. ŁK conceptualised the study, collected the data and revised the manuscript. WS and AB-P designed the study, collected the data and revised the manuscript. AA and IG analysed the data and revised the manuscript. JK collected the data and revised the manuscript. JW conceptualised and designed the study, analysed the data, revised the manuscript, supervised the study and acts as the guarantor of the study.

    • Funding JKN received a stipend from the Polish National Science Centre (DEC-2015/16/T/NZ5/00168) and was supported by ProScience of Poznan University of Medical Sciences. IG received a support from the Foundation for Polish Science within the Smart Growth Operational Programme 2014–2020 (TEAM Programme; POIR.04.04.00-00-5C9B/17–00).

    • Competing interests JKN: Received personal fees from Norsa Pharma and non-financial support from Nutricia. LK: Received personal fees from Nutricia, Vitaflo, Recordati and non-financial support from Nutricia and Recordati. AB-P: Received personal fees from Nutricia, Sanofi and Vitaflo. JW: Received personal fees and non-financial support from Biocodex, BGP Products, Chiesi, Hipp, Humana, Mead Johnson Nutrition, Merck Sharp & Dohme, Nestle, Norsa Pharma, Nutricia, Roche, Sequoia Pharmaceuticals, and Vitis Pharma, as well as research grants, personal fees and non-financial support from Nutricia Research Foundation Poland, outside the submitted work. All other authors report no disclosures.

    • Patient consent for publication Not required.

    • Ethics approval This study obtained ethics approval from Bioethical Committee at Poznan University of Medical Sciences 861/15 and 201/18.

    • Provenance and peer review Not commissioned; externally peer reviewed.