PIK3CD and Down syndrome: Patients with a conclusive diagnosis from the antibody deficiency category were diagnosed with activated PI3K-delta syndrome (APDS1) (n=2/5; 40%), X-linked agammaglobulinemia (XLA) (n=2/5; 40%) and AID deficiency (n=1/5; 20%), based on pathogenic variants in PIK3CD, BTK and AICDA, respectively.