BTK and inborn error of immunity: In humans, loss of function mutations and deletions of the BTK gene are responsible for the rare genetic condition X-linked agammaglobulinaemia, characterized by primary immunodeficiency, due to reduced circulation of B-cells and hypogammaglobulinaemia.77 The role of BTK in the maintenance of immunity should be considered in the development of inhibitors for long-term use, along with potential implications for immunosuppression from long-term administration.