In particular, aberrant CXCR4 signaling caused by heterogeneous mutations affecting the C-terminal (C-ter) region of the receptor has been reported in a rare primary immunodeficiency, the Warts, Hypogammaglobulinaemia, Infections and Myelokathexis (WHIM) syndrome [5], and more recently in Waldenstrom’s macroglobulinaemia (WM), an indolent form of B-cell non-Hodgkin lymphoma [6]. Here, CXCR4 is linked to Waldenstrom macroglobulinemia.