1. Division of Rehabilitation Care Services, VA Puget Sound Health Care System, Seattle, WA
2. Seattle Epidemiologic Research and Information Center, VA Puget Sound Health Care System, Seattle, WA
3. Clinical Learning, Evidence, and Research (CLEAR) Center, University of Washington, Seattle, WA
4. Department of Rehabilitation Medicine, University of Washington, Seattle, WA
5. Department of Natural Sciences, Novosibirsk State University, Novosibirsk, Russia
6. Laboratory of Recombination and Segregation Analysis, Institute of Cytology and Genetics, Novosibirsk, Russia
7. Department of Twin Research and Genetic Epidemiology, School of Life Course Sciences, King’s College London, London, UK
8. Department of Biology, School of Biological and Behavioural Sciences, Queen Mary University of London, UK