A 10-ml sample of venous blood was drawn from each participant, and DNA was isolated with a salting-out procedure [23]. All allele types were determined independently by two laboratory technicians blind to subject identity. Genotyping of DRD2 TaqI A polymorphism was performed by PCR as described in [24]. PCR reactions contained 10 mM Tris-HCl (pH 9.0), 50 mM KCl, 200 μM each dNTP, 1.5 mM MgCl2, 0.2 μM of each primer and 1.25 units of Taq Polymerase (Promega) in a 25 μl volume containing 50 ng sample DNA. The reaction mixture was denatured 4 min at 94°C, followed by 35 cycles of 94°C for 30 sec, 58°C for 30 sec, 72°C for 30 sec, and a final extension of 5 min at 72°C. Subsequently, 10 μl of the PCR product were digested with 5 units of TaqI restriction enzyme at 65°C overnight. The resulting products were analysed by electrophoresis and visualised under ultraviolet light. The A1-A2 genotype is revealed by three fragments (310-bp, 180-bp and 130-bp), the A2-A2 genotype by two fragments (180-bp and 130-bp), and the A1/A1 genotype is shown by an uncleaved 310-bp fragment.
