Sample collection has been described in detail elsewhere 8 (link). Genomic DNA was extracted from peripheral blood leukocytes using the Blood DNA extraction kit (Qiagen, Valencia, CA, USA) according to the manufacturer's instructions. Briefly, 200 to 300 μl blood samples stored in EDTA tubes at -80°C were equilibrated at room temperature and then mixed with protease K digestion reagent. The reaction mixtures were incubated at 56 °C for 10 minutes, then 100% ethanol was added and the mixture was spun through the extraction column. The column membrane was washed and then the DNA was eluted with 100 μl elution buffer (AE). The isolated DNA concentration was calculated with a Nano-Drop 8000 spectrophotometer (Thermo Scientific). The DNA purity was determined by calculating the A260/A280 and A260/A230 ratios.