PIK3R1 and Recurrent upper respiratory tract infections: Here, we investigated four Japanese cases with APDS2 carrying a heterozygous mutation in PIK3R1. Elkaim et al. recently summarized the clinical and immunological aspects of 36 genetically diagnosed APDS2 patients and revealed that recurrent upper respiratory tract infections (100%), pneumonitis (71%), and chronic lymphoproliferation (89%) were the most common clinical features (11).