Early studies that have identified the role of CXCL12/CXCR4 in human immunodeficiency virus (HIV) pathogenesis [52,53], later in cancer progression and metastasis [54] and more recently in the pathogenesis of WHIM syndrome [55] have facilitated research devoted to the regulation of this signalling axis. The gene discussed is CXCL12; the disease is WHIM syndrome.