Genomic DNA Extraction and Genotyping

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)].