APDS is caused by gain-of-function (GOF) mutations in the PIK3CD gene, located on chromosome 1p36, which encodes the catalytic subunit p110δ of phosphoinositide 3-kinase delta (PI3Kδ) (APDS1), or in the PIK3R1 gene, which encodes the regulatory subunit p85α (APDS2) [2]. This evidence concerns the gene PIK3CD and activated PI3K-delta syndrome.