IN-VIVO NMR-SPECTROSCOPY IN PATIENTS WITH PHENYLKETONURIA - CHANGES OF CEREBRAL PHENYLALANINE LEVELS UNDER DIETARY-TREATMENT

Localized proton magnetic resonance spectroscopy at short echo times w as used to measure phenylalanine (Phe) in parieto-occipital periventri cular brain. Six treated adult patients with phenylketonuria were inve stigated repeatedly following reinstitution of a Phe-restricted diet. Difference spectroscopy clearly enabled the identification of elevated cerebral Phe levels by subtracting spectra obtained from healthy volu nteers. Estimates of absolute brain concentrations always yielded valu es well below the serum levels with ratios [Phe](brain)/[Phe](serum) r anging from 0.27 to 0.63. A plot of [Phe](brain) versus [Phe](serum) c ould be fitted to a straight line (R = 0.90) if [Phe](serum) was below 1.3 mM. Measurements at higher serum levels could only be performed i n one patient and yielded brain Phe concentrations of 0.63 +/- 0.10 mM suggesting a saturation of the carrier systems. The feasibility to qu antify Phe transport across the blood-brain barrier in humans non-inva sively employing in-vivo proton spectroscopy can effectively improve t he prognostic significance of serum data.