Phenylalanine and Its Impact on Cognition

  • End date
    Aug 26, 2021
  • participants needed
  • sponsor
    University Hospital Inselspital, Berne
Updated on 26 January 2021
neonatal screening


The PICO-Study is a randomized, placebo-controlled, crossover, non-inferiority trial conducted to add evidence to the current European treatment guidelines for adult patients with phenylketonuria.


Phenylketonuria (PKU) is a rare autosomal recessive disorder caused by deficiency of the phenylalanine hydroxylase enzyme leading to an impaired conversion of the amino acid phenylalanine (Phe) to tyrosine. Increased Phe concentrations in blood and brain during childhood can lead to severe intellectual disability, epilepsy and behavioral problems. However, since the introduction of newborn screening and early treatment with a dietary restriction of Phe (low protein diet) and Phe-free protein substitutes (amino acid mixtures) initiated soon after birth, patient with PKU no longer develop profound and irreversible intellectual disability. While there is a wide agreement on the treatment strategy and target Phe concentrations in childhood, no consensus on the safe Phe concentrations in adulthood has been reached so far. Traditionally, the low protein diet had been enforced only during childhood and adolescence, leaving adult patients with PKU "off-diet". Over the last decade, observational and cross-sectional studies associated high Phe in early-treated adult patients with cognitive problems, psychiatric symptoms and behavioral abnormalities. These association studies and one small interventional study led to substantially differing recommendations of national and international guidelines with regard to Phe target levels in adult patients with PKU. One of these guidelines is the highly controversial grade D recommendation of the most recent European guidelines to keep Phe concentrations below 600 mol/L throughout adulthood. Consequently, the recommendations are not only unequally accepted by the treating metabolic specialists, more than 50 % of adults with PKU exhibit substantial difficulty in maintaining the compliance necessary to reach the recommended target Phe concentrations. Therefore, prospective intervention studies in adult patients with PKU are strongly needed to evaluate the effects of dietary restrictions on cognition, cerebral markers and quality of life. The PICO-Study aims at adding evidence to current guidelines and improving treatment recommendations. To this end, adult patients with PKU will participate in a randomized, placebo-controlled, double-blind, crossover, non-inferiority trial. With the intervention, the project evaluates the impact of temporarily elevated blood Phe levels on cognition and functional properties of the brain of adult patients. Results of the PICO-Study will help to increase knowledge about impaired cognitive functioning and neural abnormalities in adult patients with PKU and will improve guidelines on dietary treatment in these patients. Such guidelines can greatly influence clinical routine as well as patients' adherence to their diet and ultimately their quality of life.

Condition Phenylketonuria
Treatment Placebo, Phenylalanine, Phenylalanine
Clinical Study IdentifierNCT03788343
SponsorUniversity Hospital Inselspital, Berne
Last Modified on26 January 2021


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Inclusion Criteria

Is your age greater than or equal to 18 yrs?
Gender: Male or Female
Do you have Phenylketonuria?
Do you have any of these conditions: Do you have Phenylketonuria??
Age 18 years
Comparable to patients with regard to age, gender and educational level
Capable of following the study design
Written informed consent

Exclusion Criteria

Known or suspected drug or alcohol abuse
Change in medications likely to significantly interfere with cognitive function testing
Women who are pregnant or intent to get pregnant during the course of the study or who are breast feeding
Inability to follow the procedures of the study, e. g. due to language problems (lack of fluency in German or French), psychological disorders, dementia, etc. of the participant
Participation in another interventional study within the 30 days preceding and during the present study
Previous enrolment into the current study
Conditions interfering with MRI such as magnetic (metallic) particles in the skull or brain, cardiac pacemaker, deep brain stimulators, cochlear implant, braces or permanent retainers
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