One of the best examples is type 2 (T2) asthma, a complex endotype characterized by eosinophilic inflammation and responsiveness to specific biologics targeting the interleukin (IL) IL-4 IL-13, IL-5 or immunoglobulin (Ig) E driven pathogenetic pathwaysDisease endotypes are not fixed entities as they can shift in the same patient following environmental exposure. The gene discussed is IL4; the disease is asthma.