1. Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina, U.S.A.
2. ^*Department of Pediatrics, University of Münster, Münster, Germany
3. ^†Department of Physical Chemistry, University of Münster, Münster, Germany
4. ^‡Department of Pediatrics, University Hospital Eppendorf, Hamburg, Germany

Correspondence: Harald E Möller, Center for In Vivo Microscopy, Duke University Medical Center, P.O. Box 3302, Durham, NC 27710 U.S.A.

Received 28 October 1997; Revised 18 February 1998; Accepted 24 February 1998.

Abstract

In vivo nuclear magnetic resonance spectroscopy can be used to measure intracerebral phenylalanine (Phe) concentrations in patients with phenylketonuria (PKU). Stationary levels, obtained under free nutrition, as well as time courses after an oral Phe load (100 mg/kg) were investigated in 11 PKU patients and were correlated with the individual clinical outcome. At blood levels around 1.2 mmol/L, brain Phe was 0.41 to 0.73 mmol/L in clinically "typical" patients, but less than 0.15 mmol/L in three untreated, normally intelligent, adult women. Kinetic investigations revealed higher transport Michaelis constants and lower ratios of the brain influx and consumption rates in these women than in the "typical" control patients (K_t,app = 0.45 to 1.10 mmol/L versus 0.10 mmol/L; T_max/v_met = 2.55 to 3.19 versus 7.8 to 14.0). Such variations seem to be major causative factors for the individual vulnerability to PKU.