Although these two diseases share many similarities in immunopathology (e.g., the infiltration of T-cell cells, eosinophils and mucosal MCs, the pattern of membrane collagen deposition, the epithelial integrity, the key role of IL-4 and IL-5), they profoundly differ in two key features: abnormal airway smooth muscle (ASM) function characterizes asthma as an obstructive pulmonary disease, whereas in EB pulmonary function tests are normal. The gene discussed is IL4; the disease is asthma.