Both of these diseases are caused by mutations in the β-globin gene (HBB), which encodes two of the four hemoglobin chains, with beta-thalassemia being caused by various loss-of-function mutations that result in decreased expression or loss of function of the protein, and SCD being caused by a point mutation that results in the substitution of glutamate for valine in the active center, which affects the structure of hemoglobin and ultimately changes the shape of red blood cells. The gene discussed is HBB; the disease is Beta-thalassemia.