In early stage HIV infection, at most, only about 15% are dual/mixed (DM) tropic for CCR5 and CXCR4 [7,8], then in late disease stages, DM tropism or pure CXCR4 tropism reaches up to 60% when measured by the enhanced tropism assay [9], and is the highest with CD4 ≤ 200 cells/ml [10,11]. The gene discussed is CXCR4; the disease is HIV infectious disease.