Patients harboring x4 viruses progress to AIDS more rapidly than those harboring exclusively r5 viruses implying that CXCR4 utilization is linked to a stronger pathogenic phenotype and a switch to CXCR4 utilization is a causative factor in disease progression, this has been mainly studied in subtype B [28, 30, 31]. This evidence concerns the gene CXCR4 and AIDS.