Genetic etiologies of leukocyte adhesion defects.

Up to now three distinct syndromes affecting several steps in the leukocyte adhesion cascade have been described. In LAD I the firm adhesion of leukocyte to the endothelium is defective, because of mutations in the gene encoding the beta(2)-integrin. Recent works both in human and animal models shed light on various mutations and their physiological importance. Furthermore, the beneficial effect of gene therapy is also becoming clear. LAD II which involved the first phase of the cascade, the rolling phase, is caused by mutations in the specific fucose transporter to the Golgi apparatus. Gene targeted mice were able to demonstrate indeed the role of this transporter in the adhesion process and long-term follow-up of patients showed that while in childhood immunodeficiency is the prominent feature, later on in life the metabolic consequences govern the clinical pictures. LAD III is the last syndrome to be described and a primary activation defect in all three beta-integrins 1, 2, and 3 is detected. Just recently mutations in Kindlin 3, a newly recognized component, which binds the cytoplasmic tail of integrin, and is important in integrin activation, the second phase of the adhesion cascade, were found.