Th. Polanski¹, M.R. Zurflüh¹, L. Kierat¹, M. Demirkol², L. Fiori³, S. Sivri-Kalkanoglu⁴, B. Thöny¹, N. Blau¹

¹Division of Clinical Chemistry and Biochemistry, University Children’s Hospital, Zürich, Switzerland, ²Istanbul Faculty of Medicine, Children’s Hospital, Department of Nutrition and metabolism, Istanbul, Turkey, ³Department of Pediatrics, San Paolo Hospital, University of Milan, Milano, Italy, ⁴Nutrition and Metabolism Unit, Department of Pediatrics, Hacettepe University, Ankara, Turkey

A method for the measurement of pterins (total neopterin and biopterin) in filter paper blood spots was introduced as an alternative for the screening of BH4 deficiencies in urine. This new method enables measurement of pterins, DHPR activity, and amino acids (Phe and Tyr) from a single filter paper specimen. During the last two years we analyzed more than 800 urine specimens from patients with hyperphenylalaninemia and in 222 of them pterins were measured in dried blood spots in parallel. During this period we diagnosed 12 patients with PTPS deficiency, 22 patients with DHPR deficiency, and 1 patient with GTPCH deficiency. In patient with the GTPCH deficiency and in all patients with PTPS deficiency, both urine and dried blood pterins pattern were diagnostic. In DHPR deficiency blood spot pterins were indicative in only 7/22 patients (specificity 32%) and urinary pterins in only 12/22 patients (specificity 55%). Diagnosis of DHPR deficiency was established in all patients by measurement of enzyme activity in blood spots. Following reference values were established for pterins in dried blood spots (median; 5-95 perc.): neopterin = 1.37 (0.34-4.72) nmol/g Hb; biopterin = 0.86 (0.20-3.48) nmol/g Hb; %biopterin = 38.1 (14.2-72.2). PTPS deficiency; neopterin 4.87 (2.32-7.94) nmol/g Hb; biopterin = 0 nmol/g Hb; %biopterin = 0. DHPR deficiency: neopterin = 1.00 (0.32-3.42) nmol/g Hb; biopterin = 0.81 (0.26-3.16) nmol/g Hb; %biopterin = 38.6 (18.5-79.8). GTPCH deficiency: neopterin = 0.06 nmol/g Hb; biopterin = 0 nmol/g Hb; %biopterin = 0. Our data confirm the usefulness of dried blood spots for the diagnosis of BH4 deficiencies; however DHPR activity measurement remains an essential test. Pterins, DHPR activity, and amino acids can be measured from the single filter paper specimen. Out of 877 samples we analyzed during the last 3 years, 35 were diagnostic for BH4 deficiency (4%).