Activated PI3 Kinase Delta Syndrome: Molecular Pathogenesis and Emerging Therapeutics

Activated PI3 kinase delta syndrome (APDS) is a rare, inherited primary immunodeficiency characterized by gain-of-function mutations in the PIK3CD or PIK3R1 genes, resulting in hyperactivation of the PI3Kδ pathway and consequent immune dysregulation. This review provides an in-depth exploration of the genetic and molecular mechanisms underlying APDS, highlighting the complex interplay between immunodeficiency and autoimmunity. Clinical manifestations include recurrent infections, lymphoproliferation, autoimmune cytopenias, and inflammatory complications, which often begin in early childhood. Diagnostic strategies have evolved with the advent of genetic sequencing and immunologic biomarkers, enabling the more accurate identification and classification of APDS subtypes than previously possible. Therapeutic advances, particularly the development of PI3Kδ inhibitors such as leniolisib and duvelisib, have significantly improved patient outcomes by targeting the underlying molecular defects. Additional management approaches include immunoglobulin replacement, immunomodulators, and hematopoietic stem cell transplantation in severe cases. Despite these advances, challenges such as delayed diagnosis, treatment-related complications, and variability in clinical presentation persist. Continued research on targeted therapies, long-term outcomes, and gene-editing technologies is essential to optimize care and enhance the quality of life for individuals with APDS.