The observation that homozygosity for a 32-base pair deletion in the coding region of CCR5 (CCR5Δ32) accounted for reduced HIV infection risk was independently reported by three groups (Dean et al. 1996; Liu et al. 1996; Samson et al. 1996) within months of the identification of CCR5 as an important co-receptor for HIV viral entry (Choe et al. 1996; Deng et al. 1996; Doranz et al. 1996; Dragic et al. 1996; Rucker et al. 1996; Alkhatib et al. 1997). This evidence concerns the gene CCR5 and HIV infectious disease.