title: Reduced cerebral fluoro-L-dopamine uptake in adult patients suffering from phenylketonuria.
abstract: Deficiency of phenylalanine hydroxylase activity in phenylketonuria (PKU) causes an excess of phenylalanine (Phe) throughout the body, predicting impaired synthesis of catecholamines in the brain. To test this hypothesis, we used positron emission tomography (PET) to measure the utilization of 6-[18F]fluoro-L-DOPA [corrected] (FDOPA) in the brain of adult patients suffering from PKU and in healthy controls. Dynamic 2-h long FDOPA emission recordings were obtained in seven adult PKU patients (five females, two males; age: 21 to 27 years) with elevated serum Phe levels, but lacking neurologic deficits. Seven age-matched, healthy volunteers were imaged under identical conditions. The utilization of FDOPA in striatum was calculated by linear graphical analysis (k3S, min(-1)), with cerebellum serving as a nonbinding reference region. The time to peak activity in all brain time-radioactivity curves was substantially delayed in the PKU patients relative to the control group. The mean magnitude of k3S in the striatum of the PKU patients (0.0052+/-0.0004 min(-1)) was significantly lower than in the control group (0.0088+/-0.0009 min(-1)) (P<0.001). There was no significant correlation between individual serum Phe levels and k3S. The unidirectional clearance of FDOPA to brain was impaired in adult patients suffering from PKU, presumably reflecting the competitive inhibition of the large neutral amino acid carrier by Phe. Assuming this competition to be spatially uniform, the relationship between striatum and cerebellum time-activity curves additionally suggests inhibition of DOPA efflux, possibly also due to competition from Phe. The linear graphical analysis shows reduced k3S in striatum, indicating reduced DOPA decarboxylase activity.
authors.affiliation: Department of Nuclear Medicine, University of Mainz, Mainz, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Landvogt
authors.forename: Eugen
authors.initials: E
authors.lastname: Mengel
authors.forename: Peter
authors.initials: P
authors.lastname: Bartenstein
authors.forename: Hans Georg
authors.initials: HG
authors.lastname: Buchholz
authors.forename: Mathias
authors.initials: M
authors.lastname: Schreckenberger
authors.forename: Thomas
authors.initials: T
authors.lastname: Siessmeier
authors.forename: Armin
authors.initials: A
authors.lastname: Scheurich
authors.forename: Reinhold
authors.initials: R
authors.lastname: Feldmann
authors.forename: Josef
authors.initials: J
authors.lastname: Weglage
authors.forename: Paul
authors.initials: P
authors.lastname: Cumming
authors.forename: Fred
authors.initials: F
authors.lastname: Zepp
authors.forename: Kurt
authors.initials: K
authors.lastname: Ullrich
mesh_terms: D000328:Adult; D003342:Corpus Striatum / Q000378:metabolism*; D004295:Dihydroxyphenylalanine / Q000378:metabolism*; D005260:Female; D005462:Fluorine Radioisotopes / Q000378:metabolism; D006801:Humans; D008297:Male; D010661:Phenylketonurias / Q000503:physiopathology*; D049268:Positron-Emission Tomography
chemical_list: D005462:Fluorine Radioisotopes; D004295:Dihydroxyphenylalanine