An infant with a history of delayed separation of umbilical cord now presents with recurrent pneumonia. The total count is 20,000/ml. Which of the following genetic defects is most likely present?

This childs history of delayed separation of umbilical cord with recurrent pneumonia and peripheral leucocytosis is highly suggestive of leucocyte adhesion defect (LAD). Neutrophils have reduced adhesion, mobility and phagocytic ability. There are three types of LAD: LAD 1: Defective beta 2 integrin (CD18), leading to abnormal neutrophil chemotaxis and defective tight adhesion. LAD 2: Reduced phagocyte surface expression of Sialyl-Lewis x, leading to abnormal neutrophil rolling. LAD 3: Defective signaling for integrin activation, leading to abnormal neutrophil chemotaxis and adhesion. (Milder than type 1) Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition