Activating, autosomal-dominant and de novo mutations in PIK3CD and PIK3R1 have been discovered in patients with primary immunodeficiencies, and this condition is called activating PI3K delta syndrome (APDS), which is also referred to as PASLI (p110 delta activating mutation causing senescent T cells, lymphadenopathy, and immunodeficiency). Here, PIK3R1 is linked to inborn error of immunity.