Saliva DNA was collected and purified using the Oragene-Discover kit (DNA Genotek) following the manufacturer instructions. Saliva DNA was extracted using DNeasy Blood and Tissue kit (Qiagen) with the following modifications: 5 ml AL-buffer and 200 l Proteinase K were added to collected saliva in buffer and incubated at 56°C for 30 minutes. DNA was extracted using 4 extraction columns in parallel to optimize the yield.