PICO study

A study to test the effect of phenylalanine on brain functions

Due to a rare metabolic defect, patients suffering from phenylketonuria (PKU) cannot process the amino acid phenylalanine (Phe). A build-up of Phe in the body causes severe brain damage and developmental disorders in children. To avoid this build-up, a low-Phe (i.e. low-protein) diet must be followed in children with PKU. To what extent adult patients with PKU must follow such a strict diet remains unclear to this day. The PICO study investigates the influence of increased Phe levels on the adult brain of patients with PKU. For this purpose, a short-term break in the Phe-free diet is simulated by administering Phe capsules and changes in the brain are examined with the help of neuropsychological tests, structural and functional MRI.

Financial support

  • Swiss National Science Foundation (SNSF)
  • Vontobel-Foundation
  • Bangerter-Rhyner Foundation
  • Nutricia Metabolics Research Fund
  • Research Grant Inselspital Bern
  • Fondation Rolf Gaillard
  • Foundation for the Promotion of Nutrition Research in Switzerland
  • Department of Diabetes, Endocrinology, Nutritional Medicine and Metabolism, Inselspital, Bern University Hospital and University of Bern 


  • Bern University Hospital and University of Bern: PD Dr. Johannes Slotboom, PD Dr. rer. nat. Christian Rummel, Prof. Dr. sc. nat. Roland Kreis, PD Dr. med. Yosuke Morishima
  • Maastricht Brain Imaging Center, Maastricht University, Niederlande: Prof. Dr. Bernadette Jansma
  • University of Zurich: Prof. Dr. Nicolas Langer