Sickle Cell Disease

Sickle cell disease is a general term for a group of genetic disorders caused by sickle hemoglobin (Hgb S). In many forms of the disease, the red blood cells change shape upon deoxygenation because of polymerization of the abnormal sickle hemoglobin. This process damages the red blood cell membrane, and can cause the cells to become stuck in blood vessels. This deprives the downstream tissues of oxygen and causes ischemia and infarction. The disease is chronic and lifelong. Individuals are most often well, but their lives are punctuated by periodic painful attacks. In addition to periodic pain, there may be damage of internal organs, such as stroke. Lifespan is often shortened. It is common in people from parts of the world where malaria is or was common, especially in West Africa or in descendents of those peoples. Sickle cell disease can occur in any individual of any color or ethnicity, however.

"Sickle cell anemia" is the name of a specific form of sickle cell disease in which there is homozygosity for the mutation that causes Hgb S. Other forms of sickle cell disease include sickle-hemoglobin C disease, sickle beta-plus-thalassemia, and sickle beta-zero-thalassemia. Unlike sickle cell anemia, these other forms of sickle cell disease are compound heterozygous states in which the person has only one copy of the mutation that causes Hgb S and one copy of another abnormal hemoglobin gene. It is important to know that "sickle cell anemia" is the proper name of a specific type of "sickle cell disease", and that "sickle cell disease" is a non-specific term. Because the different forms of sickle cell disease are quite different, one must be sure to specify the exact form of the disease in question.

Signs and symptoms

Patients with sickle cell anemia have steady-state or baseline anemia that varies in severity, with hemoglobin levels of 6-9 g/dl typical. Reticulocyte counts are elevated, reflecting new red blood cells replacing the rapidly destroyed older cells - red blood cell life span is markedly reduced in this disease. Often, the white blood cell and platelet counts are elevated, and these cells may contribute to vaso-occlusion.

Diagnosis

Attacks are diagnosed clinically, i.e. there is no gold standard diagnostic test. Hemolysis (anemia and jaundice) is often present, although for painful crises the diagnosis depends essentially on how the patient describes the pain.

Abnormal hemoglobin forms are detected on hemoglobin electrophoresis, a form of gel electrophoresis on which the various types of hemoglobin move at varying speed. Sickle cell hemoglobin (HbSS) and Hemoglobin C with sickling (HbSC)--the two most common forms--can be identified from there. Genetic testing is rarely performed.

History

The cause of this collection of clinical findings was unknown until the description of the sickle cells in 1910 by the Chicago cardiologist and professor of medicine James B. Herrick (1861-1954) whose intern Ernest Edward Irons (1877-1959) found "peculiar elongated and sickle shaped" cells in the blood of Walter Clement Noel, a 20 year old first year dental student from Grenada after Noel was admitted to the Presbyterian Hospital in December 1904 suffering from anemia. Noel was readmitted several times over the next three years for "muscular rheumatism" and "bilious attacks" while an undergraduate. Noel completed his studies and returned to capital of Grenada (St. George's) to practice dentistry. He died of pneumonia in 1916 and is buried in the Catholic cemetery at Sauteurs in the north of Grenada.

The disease is very occasionally called "Herrick's syndrome" for this reason.

The disease was named "sickle cell anemia" by Vernon Mason in 1922. In retrospect some elements of the disease had been recognized earlier: a paper in the Southern Journal of Medical Pharmacology in 1846 described the absence of a spleen in the autopsy of a runaway slave. The African medical literature reported this condition in the 1870's where it was known locally as ogbanjes ('children who come and go') because of the very high infant mortality in this condition. Also, the practice of using tar soap to cover blemishes caused by sickle cell sores was prevalent in the African American community.