PIK3CD and immunodeficiency 36 with lymphoproliferation: APDS-1 arises from autosomal dominant gain-of-function mutations in the PIK3CD gene that encodes for the catalytic (p110δ) subunit of phophotidylinositol 3-kinase (PI3K), while monoallelic loss-of-function mutations in PIK3R1, which encodes for the regulatory (p85α) subunit of PI3K, causes APDS-2 [64].