Oragene dna og 500 collection tubes

Saliva samples were collected from the participants using the Oragene DNA OG-500 collection tubes (DNA Genotek, Inc., Ottawa, Ontario, Canada). DNA was extracted according to the prepIT.L2P manual protocol provided by the manufacturer. DNA quality was checked using agarose gel electrophoresis and NanoDrop spectrophotometer.

Biological samples were collected as either a venous blood or saliva sample. Briefly, 5 mL of blood was collected from a superficial forearm vein by a trained phlebotomist into 5 mL EDTA tubes (BD Vacutainer Systems, Plymouth, UK). Samples were stored at −20 °C before further processing. Saliva samples were collected using Oragene DNA OG-500 collection tubes (DNA Genotek Inc., ON, Canada) following the manufacturer’s instructions and stored at room temperature until DNA extraction. Genomic DNA was extracted from the collected samples using a QIAcube, QIAamp DNA Blood Mini kit and standard spin column protocol (Qiagen, Crawley, UK). For genotyping, two techniques were used; EP1 Fluidigm (Fluidigm, Cambridge, UK) and StepOnePlus (Applied Biosystems^®, Paisley, Scotland, UK). A brief description of genotyping procedures using both techniques is presented in our previous papers [36 (link),37 (link)] and the genotypes for the selected SNPs were called based on end-point fluorescence (https://www.thermofisher.com/np/en/home.html) (attached in Table S2). All samples were analysed in duplicate [38 (link)].