deCODE Genetics represents a large population-based Icelandic sample. The Icelandic cigarette smoking data have been described elsewhere.4 All Icelandic subjects in the study of smoking-related phenotypes, including Icelandic population controls, were originally recruited for different genetic studies, conducted over 18 years (1996–2014) at deCODE Genetics. Questionnaire data were used to gather information on CPD and the FTND score. The deCODE Genetics studies were approved by the Data Protection Commission of Iceland and the National Bioethics Committee of Iceland. Personal identifiers associated with phenotypic information and blood samples were encrypted using a third-party encryption system.18 Altogether, we included data for 9090 smokers who were genotyped using SNP arrays in one of several GWAS conducted by deCODE Genetics. Genotyping was carried out using Illumina (San Diego, CA, USA) chips. QC was carried out as previously described.19
