The hallmarks of leucocyte adhesion deficiency (LAD) are defects in the leucocyte adhesion process,
marked leukocytosis and recurrent infections. These molecular and clinical manifestations result from an
impaired step in the inflammatory process, namely, the emigration of leukocytes from the blood vessels to
sites of infection, which requires adhesion of leukocytes to the endothelium. In the last 20 years, three
distinctive defects in the leucocyte adhesion cascade, involving several precise ordered steps such as
rolling, integrin activation and firm adhesion of the leukocytes have been described. While LAD I and II are
clearly autosomal recessive disorders, the mode of inheritance of LAD III is still not clear. LAD I is due to
structural defects in the integrin molecule, preventing a firm adhesion to occur. In LAD II, the primary
genetic defect is in a specific Golgi GDP-fucose transporter that leads to absence of the selectin ligand on
the leukocyte and a defective rolling. LAD III or LADI/variant, which was last described, is due to defects in
the integrin activation process. All three syndromes are very rare, LAD I being more frequent than LAD II
and III, with LAD I being described in more than 300 patients worldwide and LAD II and III in less than 10
children each. The most important focus should be to control infections. Treatment includes antibiotics and
in many cases bone marrow transplantation.