The First Iranian Cohort of Pediatric Patients with Activated Phosphoinositide 3-Kinase-δ (PI3Kδ) Syndrome (APDS).

Background: Activated phosphoinositide 3-kinase δ syndrome (APDS) is a recently defined combined primary immunodeficiency disease (PID) characterized by recurrent respiratory tract infections, lymphoproliferation, autoimmunity and lymphoma. Gain-of-function mutations in PIK3CD and loss-of-function of PIK3R1 genes lead to APDS1 and APDS2, respectively.Methods: Demographic, clinical, immunological and genetic data were collected from medical records of 15 pediatric patients, who were genetically identified using the whole-exome sequencing method.Results: Fifteen patients (6 APDS1 and 9 APDS2) were enrolled in this study. Recurrent respiratory tract infections followed by lymphoproliferation and autoimmunity were the most common manifestations (86.7%, 53.3% and 26.7%, respectively). Five patients (33.3%) had a Hyper-IgM-syndrome-like immunoglobulin profile. In the APDS1 group, splice site and missense mutations were found in half of the patients and the C-lobe domain of PIK3CD was the most affected region (50%). In the APDS2 group, splice site mutation was the most frequent mutation (77.8%) and the inter-SH2 domain was the most affected region of PIK3R1 (66.7%). Mortality rate was significantly higher in APDS2 group (P = .02) mainly due to chronic lung infections.Conclusion: Respiratory tract infections and humoral immunodeficiency are commonly the most important complication in pediatric APDS patients, and they can be fatal by ultimately causing catastrophic damage to the structure of lungs. Hence, physicians should be aware of its significance and further work-up of patients with recurrent respiratory tract infections especially in patients with lymphoproliferation. Moreover, delineation of genotype-phenotype associations with disease severity could be helpful in the timely application of appropriate management and patients' survival.