Open Peer Review Any reports and responses or comments on the article can be found at the end of the article. RESEARCH ARTICLE Assessment of dried blood spots for DNA methylation profiling [version 1; referees: awaiting peer review] Rosie M. Walker , Louise MacGillivray , Sarah McCafferty , Nicola Wrobel , Lee Murphy , Shona M. Kerr , Stewart W. Morris , Archie Campbell , Andrew M. McIntosh , David J. Porteous , Kathryn L. Evans 1,2* Medical Genetics Section, Centre for Genomic and Experimental Medicine, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, Midlothian, EH4 2XU, UK Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh, Edinburgh, Midlothian, EH4 2XU, UK Edinburgh Clinical Research Facility, Western General Hospital, University of Edinburgh, Edinburgh, Midlothian, EH4 2XU, UK MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, Midlothian, EH4 2XU, UK Generation Scotland, Centre for Genomic and Experimental Medicine, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, Midlothian, EH4 2XU, UK Division of Psychiatry, University of Edinburgh, Edinburgh, Midlothian, EH4 2XU, UK Equal contributors Abstract DNA methylation reflects health-related environmental Background: exposures and genetic risk, providing insights into aetiological mechanisms and potentially predicting disease onset, progression and treatment response. An increasingly recognised need for large-scale, longitudinally-profiled samples collected world-wide has made the development of efficient and straightforward sample collection and storage procedures a pressing issue. An alternative to the low-temperature storage of EDTA tubes of venous blood samples, which are frequently the source of the DNA used in such studies, is to collect and store at room temperature blood samples using purpose built filter paper, such as Whatman FTA® cards. Our goal was to determine whether DNA stored in this manner can be used to generate DNA methylation profiles comparable to those generated using blood samples frozen in EDTA tubes. DNA methylation profiles were obtained from matched EDTA tube Methods: and Whatman FTA® card whole-blood samples from 62 Generation Scotland: Scottish Family Health Study participants using the Infinium HumanMethylation450 BeadChip. Multiple quality control procedures were implemented, the relationship between the two sample types assessed, and epigenome-wide association studies (EWASs) performed for smoking status, age and the interaction between these variables and sample storage method. Dried blood spot (DBS) DNA methylation profiles were of good quality Results: and DNA methylation profiles from matched DBS and EDTA tube samples were highly correlated (mean = 0.991) and could distinguish between r participants. EWASs replicated established associations for smoking and age, with no evidence for moderation by storage method. Our results support the use of Whatman FTA® cards for Conclusions: collecting and storing blood samples for DNA methylation profiling. This 1,2 3 3 3 3 1,4 1 5 2,6 1,2,5* 1,2* 1 2 3 4 5 6 * Referee Status: AWAITING PEER REVIEW 06 Mar 2019, :44 ( First published: 4 ) https://doi.org/10.12688/wellcomeopenres.15136.1 06 Mar 2019, :44 ( Latest published: 4 ) https://doi.org/10.12688/wellcomeopenres.15136.1 v1 Page 1 of 12 Wellcome Open Research 2019, 4:44 Last updated: 07 MAR 2019