Expression analysis of purine metabolic enzymes. (A) Illustration of purine pathway. HPRT indicates hypoxanthine phosphorybosil transferase; PNP, purine nucleoside phosphorylase; MeT, methyl transferase; AK, adenosine kinase; DCK, deoxycytidine kinase; RR, ribonucleotide reductase. (B) Relative mRNA expression of SAHH, as measured with quantitative RT-PCR, in UT clones from patient 2 (n = 4; gray dots) and controls (transduced and healthy clones, n = 46; box-and-whiskers). (C) SAHH enzymatic activity. Relative mRNA expression of DCK (D) and AK (E) in UT clones and controls. P values refer to gene expression of UT clones versus controls.