Diagnosis of dopa-responsive dystonia and other tetrahydrobiopterin disorders by the study of biopterin metabolism in fibroblasts.
BACKGROUND
Dopa-responsive dystonia (DRD) and tetrahydrobiopterin (BH4) defects are inherited disorders characterized by monoamine neurotransmitter deficiency with decreased activity of one of the BH4-metabolizing enzymes. The aim of the study was to determine the utility of cultured skin fibroblasts for the diagnosis of these diseases.


METHODS
Neopterin and biopterin production and GTP cyclohydrolase I (GTPCH) activity were measured in cytokine-stimulated fibroblasts; 6-pyruvoyltetrahydropterin synthase (PTPS), sepiapterin reductase (SR), and dihydropteridine reductase (DHPR) activities were measured in unstimulated fibroblasts. We examined 8 patients with DRD, 3 with autosomal recessive GTPCH deficiency, 7 with PTPS deficiency, 3 with DHPR deficiency, and 49 controls (35 fibroblast and 14 amniocyte samples).


RESULTS
Fibroblasts from patients with DRD and autosomal recessive GTPCH deficiency showed reduced GTPCH activity (15.4% and 30.7% of normal activity, respectively) compared with controls (P < 0.001). Neopterin production was very low and biopterin production was reduced in both disorders. PTPS- and DHPR-deficient cells showed no enzyme activities; in PTPS deficiency the pattern of pterin production was typical (neopterin, 334-734 pmol/mg; controls, 18-98 pmol/mg; biopterin, 0 pmol/mg; controls, 154-303 pmol/mg). Reference values of all enzyme activities and pterin production were measured in fibroblasts and also in amniocytes for prenatal diagnosis.


CONCLUSIONS
Cultured skin fibroblasts are a useful tool in the diagnosis of BH4 deficiencies. Intracellular neopterin and biopterin concentrations and GTPCH activity in cytokine-stimulated fibroblasts are particularly helpful in diagnosing patients with DRD.
Division of Clinical Chemistry and Biochemistry, Department of Pediatrics, University of Zurich, Steinwiesstrasse 75, 8032 Zurich, Switzerland.
L
L
Bonafé
B
B
Thöny
W
W
Leimbacher
L
L
Kierat
N
N
Blau
D000429:Alcohol Oxidoreductases / Q000378:metabolism; D001708:Biopterins / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000172:deficiency* / Q000378:metabolism; D002457:Cell Extracts; D002478:Cells, Cultured; D016207:Cytokines / Q000494:pharmacology; D004093:Dihydropteridine Reductase / Q000378:metabolism; D004295:Dihydroxyphenylalanine / Q000627:therapeutic use*; D015259:Dopamine Agents / Q000627:therapeutic use*; D004421:Dystonia / Q000175:diagnosis* / Q000188:drug therapy; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D006136:GTP Cyclohydrolase / Q000378:metabolism; D006801:Humans; D008297:Male; D008661:Metabolism, Inborn Errors / Q000175:diagnosis*; D019798:Neopterin / Q000096:biosynthesis; D019761:Phosphorus-Oxygen Lyases / Q000378:metabolism; D012016:Reference Values; D012867:Skin / Q000166:cytology
D002457:Cell Extracts; D016207:Cytokines; D015259:Dopamine Agents; D001708:Biopterins; D004295:Dihydroxyphenylalanine; D019798:Neopterin; D000429:Alcohol Oxidoreductases; C022630:sepiapterin reductase; D004093:Dihydropteridine Reductase; D006136:GTP Cyclohydrolase; D019761:Phosphorus-Oxygen Lyases; C043497:6-pyruvoyltetrahydropterin synthase; C003402:sapropterin