Another study screened 669 patients with undefined PIDs for the N334K, C416R, E525K, and E1021K mutations in PIK3CD and the PIK3R1 splice site mutations and found only PIK3CD mutations in three siblings diagnosed with common variable immune deficiency (CVID) and two sporadic cases with combined immunodeficiency (23). Here, PIK3CD is linked to combined immunodeficiency.