Leukocyte adhesion deficiency
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|Classification and external resources|
Leukocyte adhesion deficiency (LAD), is a rare autosomal recessive disorder characterized by immunodeficiency resulting in recurrent infections. LAD is currently divided into three subtypes: LAD1, LAD2, and the recently described LAD3, also known as LAD-1/variant. In LAD3, the immune defects are supplemented by a Glanzmann thrombasthenia-like bleeding tendency.
LAD was first recognized as a distinct clinical entity in the 1970s. The classic descriptions of LAD included recurrent bacterial infections, defects in neutrophil adhesion, and a delay in umbilical cord sloughing. The defects adhesion result in poor leukocyte chemotaxis, particularly neutrophil, inability to form pus and neutrophilia.
Individuals with LAD suffer from bacterial infections beginning in the neonatal period. Infections such as omphalitis, pneumonia, gingivitis, and peritonitis are common and often life-threatening due to the infant's inability to properly destroy the invading pathogens. These individuals do not form abscesses because granulocytes cannot migrate to the sites of infection.
Cause and genetics
|LAD2 or CDG2C||266265||SLC35C1|
The most common type is LAD1.
The inherited molecular defect in patients with LAD1 is a deficiency of the β-2 integrin subunit, also called CD18, of the leukocyte cell adhesion molecule, which is found on chromosome 21. This subunit is involved in making three other proteins (LFA-1, Integrin alphaXbeta2, and Mac-1/CR3). This basically means the gene creates a nonfunctioning protein, which results in the lack of LFA1 integrin, which allows neutrophils to make their way out of the blood stream by adhering to the Ig family receptor ICAM on the apical surface of endothelial cells in the infected areas of the body (i.e. the lungs in pneumonia). The bacteria can then proliferate, leading to symptomatic infection. The infection can spread unimpeded and cause serious injury to important tissue.
Typically, diagnosis is made after several preliminary tests of immune function are made, including basic evaluation of the humoral immune system and the cell-mediated immune system. A WBC differential will reveal extremely elevated levels of neutrophils (on the order of 6-10x normal) because they are unable to leave the blood vessels. Specific diagnosis is made through monoclonal antibody testing for CR3, one of the three complete proteins which fail to form properly as a result of β-2 integrin subunit deficiency.
LAD is a rare disease, with an estimated prevalence of one in 100,000 births, with no described racial or ethnic predilection.
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