Background: APDS [Activated phosphoinositide 3-kinase (PI3K) δ Syndrome] is a newly found special form of primary immunodeficiency caused by mutations in genes encoding PI3Kδ subunits and over-activation of the PI3K signaling pathway. Gain-of-function and loss-of-function mutations in PIK3CD (encoding P110δ) and PIK3R1 (encoding p85α, p55α and p50α) lead to APDS1 and APDS2, respectively. The subsequent irregular PI3K downstream signaling cascade is associated with abnormalities in B cells and T cells and the consequent heterogeneous clinical manifestations including respiratory tract infections, autoimmunity, lymphoproliferation and not to mention primary antibody deficiency. In this study, we report a 12-year-old girl with a mutation in the PIK3R1 gene who manifested immunological phenotypes resembling hyper IgM syndrome along with a review of the literature of the previously reported patients. Methods: Whole exome sequencing was performed to detect the underlying genetic mutation in this patient. Results: A de novo heterozygous splice site mutation in the hot spot of the PIK3R1 gene within the intron 10 was found (c.1425+1G>A). Conclusion: Further investigations are required for evaluation of the underlying genetic defects and the possible associations between genetic underpinning and heterogeneous severity and features of the disease. Keywords: Activated phosphoinositide 3-kinase delta syndrome (APDS); APDS2; PASLI-R1; Hyper IgM syndrome; PIK3R1; p85α: primary immunodeficiency