Acute chest syndrome
Sudden onset of cough, shortness of breath, or other symptoms of lower respiratory tract disease, and a new pulmonary infiltrate on chest radiograph.

Adhesion mediators
Blood cell surface proteins that bind specific ligands on the surface of other blood, endothelium, or immune cells, causing cells to adhere and slow their movement through the bloodstream.

A variant form of a gene. Each pair of alleles represents the genotype of a specific gene. Genotypes are described as homozygous if there are two identical alleles and as heterozygous if the two alleles differ.

A reduction in the concentration of red blood cells or hemoglobin below normal levels in the blood, occurring when the equilibrium between blood loss and blood production is disturbed. Normal hemoglobin levels are >11g/dL, but in patients with SCD, levels are typically around 6-8 g/dL.


Bone pain crisis
Microvascular occlusion of the bone marrow leading to tissue ischemia and often excruciating pain.


Any disease that affects the heart muscle, diminishing cardiac performance.

Calculi (stones) in the common bile duct.

The presence or formation of gallstones.

Inflammation of the gallbladder, usually caused by obstruction of the biliary ducts by gallstones.


The pair of alleles (gene variants) present in a person for a particular characteristic or protein. The genotype is the set of genes in our DNA that is responsible for a particular trait. The phenotype is the physical expression, or characteristics, of that trait.


Hb Polymerization
When deoxygenated, abnormal hemoglobin, HbS, undergoes polymerization resulting in the sickling of red blood cells.

The iron-containing pigment of red blood cells that carries oxygen from the lungs to the tissues.

The destruction/rupture of red blood cells, resulting in the release of byproducts into the bloodstream.


Restriction of blood flow to an organ or tissue.


Multicelluar adhesion
Process involves white blood cells, red blood cells, and platelets that aggregate and adhere to endothelial cells of the vessel wall. As a result, this process promotes vaso-occlusion that leads to chronic vascular damage, which begins early in childhood.


Necrosis of bone due to obstruction of its blood supply.

Overt stroke
Cerebral ischemia and hypoxia can result in symptoms of a stroke, including cognitive and motor deficits.


Production by a single gene of multiple phenotypic effects. The term is often used to refer to a single gene defect that is expressed as problems in multiple systems of the body.

Persistent erection of the penis, accompanied by pain and tenderness, resulting from a pathologic condition rather than from sexual desire.



Selectins are signaling molecules that are expressed on activated cells and are involved in mediating adhesions between endothelial and blood cells, resulting in multiceullar adhesion and vaso-occlusion. There are 3 types of selectins: E, L, and P. E-selectin is expressed on activated endothelial cells; L-selectin is expressed on WBCs; and P-selectin is expressed on activated endothelial and platelet cells.

Sickle Cell Anemia
One type of sickle cell disease. It is used interchangeably with HbSS disease or genotype, which is typically found in people of African ancestry.

Sickle Cell Trait
People with sickle cell trait inherit one sickle gene and one normal gene from each parent. They do not have sickle cell disease, but their children are at risk for inheriting the trait or disease. People with sickle cell trait are usually asymptomatic, but may be at greater risk for certain complications associated with SCD.


A group of hereditary anemias produced by a defective production rate of the α or β hemoglobin chain or a decreased synthesis of the beta chain.


Vaso-occlusion in SCD is due to a multicellular adhesion cluster caused by white blood cells, red blood cells, and platelets that adhere to each other and the endothelial layer of blood vessels. Vaso-occlusion can result in ischemia, hypoxia, and eventual organ damage and failure.

Vaso-occlusive crisis (VOC)
VOCs are also referred to as pain crises or vaso-occlusive episodes (VOEs) and are the clinical hallmark of SCD. Ongoing vaso-occlusion can culminate in VOCs, which are extremely painful episodes that can last approximately 10 days and may require medical intervention. VOCs are associated with reduced quality of life and an increased risk of organ damage and death.

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