1 Departments of Medicine and Physiology, Faculty of Health Sciences, Universtiy of Witwatersrand, Johannesburg 2000, South Africa.
2 Division of Rheumatology and Epidemiology, Genetics and Atherosclerosis Research Group on Systemic Inflammatory Diseases, Hospital Universitario Marques de Valdecilla, Instituto de Investigacion Marques de Valdecilla (IDIVAL), 39011 Santander, Spain.
3 Department of Medicine and Psychiatry, Universidad de Cantabria, 39011 Santander, Spain.