The family protein is essential in the development and differentiation of cells in hematopoietic origin, and the defect in one of the molecules is associated with immunodeficiency (i.e., germline mutation of IKZF1 in B cell defect, combined immunodeficiency, and immunodeficiency with hematological manifestations) [25, 31–33] or with lymphoid malignancy (somatic mutation in IKZF1, IKZF2, or IKZF3 found in acute lymphoblastic leukemia, malignant lymphoma, and chronic lymphocytic leukemia) [34–37]. Here, IKZF1 is linked to combined immunodeficiency.