Hemoglobin E (HbE) disease is a genetic disorder that affects the structure and function of hemoglobin, the protein in red blood cells responsible for transporting oxygen throughout the body. This condition is caused by a mutation in the HBB gene, leading to the production of an abnormal form of hemoglobin known as Hemoglobin E. Individuals with this disorder may exhibit mild anemia, microcytosis, and hypochromia.