ORAI1 and severe combined immunodeficiency: Several studies on STIM1- and Orai1-knock-out mice as well as the severe combined immunodeficiency syndrome (SCID) associated with the Orai1 R91W mutant have demonstrated the impact of store-operated channels in physiological and pathophysiological functions of mast cells, T-lymphocytes, platelets, and smooth muscle cells (7, 14, –, 17).