Bone and Mineral Research Unit, Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), Retic REDinREN-ISCIII, Hospital Universitario Central de Asturias, 33011 Oviedo, Spain. Investigaciones Reumatológicas y Osteológicas (IRO), Buenos Aires 1114, Argentina. Center for Bone Quality, Division Endocrinology, Department of Medicine, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands. Service and Laboratory of Bone Diseases, Department of Medicine, Faculty of Medicine, Geneva University Hospital, 1211 Geneva, Switzerland. International Osteoporosis Foundation, 1260 Nyon, Switzerland.