Two mL of saliva were collected in Oragene-Discover (Oragene™, DNAgenotek, Ottawa, Ontario, Canada) kits distributed to participants through the mail. When capped, the collection vessel released a room-temperature stabilizing lysis buffer. DNA extraction and purification was conducted at the Institute for Behavior Genetics at the University of Colorado, Boulder. The DNA was prepared from 500 μl of the Oragene™ solution with the Beckman-Coulter DNAdvance (Brea, CA) system according to the manufacturer’s protocol, with the final elution volume being 150 μl. Samples were diluted 1:20 in TE and the DNA was quantified using Picogreen fluorescence (Invitrogen, ThermoFisher, Grand Island, NY). Samples were standardized to 50 ng DNA/μl for chip genotyping.
