This protocol will be investigating the use of stem cell transplantation, in related donors, to cure sickle cell disease. Sickle cell disease is a recessive disorder caused by a point mutation that results in the substitution of valine for glutamic acid at the sixth position in the B-chain of hemoglobin. This leads to sickling of the red blood cells under many conditions, such as hypoxia, dehydration, and hyperthermia. The sickling leads to vaso-occlusion, which causes irreversible damage in almost all systems in the body, including the central nervous system (CNS), lungs, heart, bones, eyes, liver, and kidneys.