Buccal swab sample collection Consenting patients who did not provide a venous blood sample were invited to provide a buccal swab for subsequent DNA extraction. Samples were collected by rubbing a sterile swab firmly against the inside of the participant's cheek or between their lips and the gum line for one minute. The swab was stored in a sterile container with a silica gel capsule (Isohelix Dri-Capsules, Cell Projects Ltd) to stabilise the sample at room temperature for up to two years.