Natural history of clinical manifestations in activated phosphoinositide 3-kinase δ syndrome (APDS): Time-to-event analyses using the European Society for Immunodeficiencies-APDS registry

Activated phosphoinositide 3-kinase delta (PI3Kδ) syndrome (APDS) is an ultra-rare, progressive disease characterised by immunodeficiency, immune dysregulation, and risk of malignancies. To further characterise the natural history of APDS, we analysed patient characteristics, manifestations, treatment use, and combinations of manifestations and combinations of treatments over time using longitudinal data from registration and follow-up visits in the European Society for Immunodeficiencies (ESID)-APDS registry. 140 patients were included (mean age: 17.7 years at registration; 19.1 years at last follow-up). Manifestation burden was high from childhood (patients experienced up to 9 manifestations by age 10). The number of treatments increased with age, with a 64 % probability of receiving ≥1 by age 10. Life-threatening APDS complications led to 13 deaths reported over 2.6 years' mean follow-up. These data highlight the chronic, progressive nature of APDS and its long-term impact on patients, with a high manifestation load and early mortality, despite widespread symptomatic treatment use.