The HBB gene provides instructions for making a protein called beta-globin, which is a subunit of a larger protein called hemoglobin. Beta-globin is located inside red blood cells. Hemoglobin normally consists of four protein subunits: two subunits of beta-globin and two subunits of another protein called alphaglobin. Each of the four protein subunits of hemoglobin carries an iron-containing molecule called heme. Heme molecules are necessary for red blood cells to pick up oxygen in the lungs and deliver it to cells throughout the body.
More than 250 mutations in the HBB gene have been found to cause beta thalassemia which is a blood disorder that reduces the production of hemoglobin and sickle cell anemia which causes distorting the red blood cell. HBB gene mutations that decrease beta-globin production result in a type of the condition called beta-plus (B+) thalassemia whereas mutations that prevent cells from producing any beta-globin result in beta-zero (B0) thalassemia.