1. Center for Epigenetics, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA.
2. Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
3. Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA.
4. Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, Baltimore, MD 21205, USA.
5. Icelandic Heart Association, Kopavogur 201, Iceland.
6. University of Iceland, Reykjavik, Iceland.
7. Intramural Research Program, National Institute of Aging, Bethesda, MD 21205, USA.
8. Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA.