One view of the pathogenesis of sickle cell diseases.

A single amino acid substitution in the beta chain of hemoglobin (beta 6 glutamic acid leads to valine) is responsible for polymerization of deoxyhemoglobin S, and the sickling of red blood cells containing that hemoglobin. Sickled cells are rigid and inflexible, causing obstruction of small blood vessels, which in turn causes obstruction of small blood vessels, which in turn causes ischemic injury. Organs most frequently damaged include the spleen, bone marrow, liver, and kidney. Sickled cells also have a shortened survival; the hemolytic anemia they produce is responsible for aplastic crises, megaloblastic anemia, ankle ulcers, gallstones and gout. "Sickle cell lung disease" is a serious problem, since distinction between infection and infarction is difficult or impossible, and impaired oxygenation of the blood makes further sickling likely. Since the entire patient, not just his blood, is affected by the disease, treatment must go beyond transfusion and drug administration. Each patient presents a new constellation of problems, and therapy must be individualized if it is to be optimal.