Neuroimaging and Neurocognitive Assessment and Response to Sapropterin Dihydrochloride Treatment in Phenylketonuria

We plan to enroll 36 subjects with PKU. They will all be counseled to follow the PKU diet. They will be randomized to receive Kuvan. We will plan to enroll 12 in the diet alone group and 24 in the Kuvan group with the hope of 12 being responders (as defined by a 30% drop in blood phe levels). Those who do not have a blood response with decreased Phe will still be evaluated for a neurological response as measured by neurocognitive testing and neuroimaging as outlined in this protocol. All 24 in the Kuvan group will receive a 1 month trial of Kuvan and then the responders will have their insurance cover the drug and for the non responders Biomarin will supply Kuvan.

Aim 1: To test the hypothesis that stable patients with PKU who are not currently on diet have specific brain biomarkers quantifiable by DTI, fMRI and MRS and that the levels of these biomarkers correlate with the clinical severity and outcome. Our pilot study and the research of others have suggested the following as potential biomarkers for neural injury in PKU:

• Metabolic abnormalities: elevated Phe concentrations as measured by MRS.
• White matter microstructure: measured by apparent diffusion coefficient, (ADC), using DTI.
• Working memory and attention/executive function: measured by fMRI, Near infrared spectroscopy (NIRS) and neuropsychological testing.

We will study these potential biomarkers in a group of well characterized adults with PKU who are not currently on diet or a strict diet as evidenced by elevated Phe, but who were identified by the newborn screen and may have been on diet during childhood, with varying severity of clinical involvement.

Aim 2: To measure changes in biomarkers validated in Aim 1 after return to diet +/- Kuvan (sapropterin dihydrochloride; Kuvan)

Based on our preliminary data and that of others, Aim 1 should provide us with a number of candidate biomarkers for brain injury in PKU. We expect that these will include three types of markers that can be correlated: metabolic, structural and cognitive. We will use these biomarkers to study subjects during return to diet and/or initiation of Kuvan.

Aim 3: To compare cognitive performance in our subjects prior to and after return to diet +/- Kuvan. using the following tests:

Comprehensive Trail making test (CTMT) -Parts A and B Stroop WASI (IQ, digit span) BRIEF Edinburgh Handedness Inventory Hand Preference Demonstration Test

Outcome variables The primary endpoints in this study are 1) an estimate of the white matter damage (macroscopic and microscopic) in participants with PKU versus controls at baseline and after return to diet +/- Kuvan; 2) determination of a profile of brain biochemical abnormalities in participants with PKU versus controls at baseline and after return to diet/Kuvan, 3) assessment of cognitive and motor systems abnormalities (by fMRI and cognitive testing) in the participant cohort as compared to age matched typically developing non disease controls at baseline and after return to diet/Kuvan; 4) coefficient of variability of scoring on traditional neurocognitive.

After the conclusion of this study, future areas of research would include expansion to study long term effects of Kuvan, study of more impaired populations and response to Kuvan, and using optical imaging methods we are currently piloting in OTCD.

Method to investigate biomarkers of disease We plan to use 1HMRS to identify markers of disease severity such as elevations of Phe and decreases in NAA. This will be compared in participants and normal age matched controls. Additionally, diffusion tensor imaging will allow us to probe white matter fiber tracts that may be especially vulnerable in this disorder selectively. Lastly, fMRI may identify regions of differential activation in the brain that are different in participants versus age matched controls at rest and with a cognitive task probing working memory and attention.