Sidra Medicine, P O Box 26999, Doha, Qatar; Weill Cornell Medical College, Doha, Qatar. Sidra Medicine, P O Box 26999, Doha, Qatar. Sidra Medicine, P O Box 26999, Doha, Qatar; Weill Cornell Medical College, Doha, Qatar; Qatar University, Doha, Qatar. Sidra Medicine, P O Box 26999, Doha, Qatar; Population Medicine, School of Medicine, Cardiff University, UK. Electronic address: cpowell@sidra.org.