Activated PI3Kδ syndrome type 2: Two patients, a novel mutation, and review of the literature.

Background: Autosomal dominant gain-of-function mutations in PIK3R1 encoding for the regulatory subunit (p85α, p55α, and p50α) of Class IA phosphoinositide 3-kinase (PI3K) result in the activated PI3Kδ syndrome (APDS) type 2 characterized by childhood-onset combined immunodeficiency, lymphoproliferation, and immune dysregulation. To improve clinical awareness and understanding of these rare diseases, we reviewed all hitherto published cases with APDS type 1 and type 2 for their clinical and immunologic symptoms and added novel clinical, immunologic, and genetic findings of two patients with APDS type 2.

Methods: Clinical, immunologic, and genetic evaluation of two new patients with APDS2 was performed followed by the systematic collection of all available previously published data of patients with APDS1 and APDS2.