BTK and agammaglobulinemia: In patients with an inborn error of immunity and an identified gene defect, the first presenting symptoms can still occur even after the age of 20, e.g., in our cohort, one patient with agammaglobulinemia due to a BTK mutation first showed manifestation of the disease at the age of 30, one patient with CSR/HIGM (Hyper-IgM) due to a PMS2 mutation showed manifestation at the age of 36, and one patient with CSR/HIGM (Hyper-IgM) due to a CD40L mutation showed manifestation at the age of 44.