Each of the subjects' DNA was extracted from whole blood at the time of diagnosis using QIAamp DNA Blood Mini Kit (Gene Company LTD., Chai Wan, Hong Kong). DNA fragments were amplified through polymerase chain reaction (PCR), which was carried out in a total volume of 10 L containing 50 ng of genomic DNA, 200 mM dNTPs, 0.3 mM/mL of each primers (5′ -CTGGAGACCACTCCCATCCTTTCT); (5′ -GATGTGGCCATCACATTCGTCAGAT) in PCR buffer with 0.5 units Taq DNA polymerase (Takara, Shiga, Japan). After the initial denaturation step (10 min at 95℃), 35 cycles were repeated for 30 sec at 94℃, 30 sec at 52℃, 90 sec at 72℃, and 5 min at 72℃. DNA fragments were then separated by electrophoresis on 2.5% agarose gel.