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To the Editor.—Stromal-derived factor (SDF-1) is the natural ligand for CXCR4, a coreceptor with CD4 for T-lymphocyte cell line–tropic human immunodeficiency virus 1 (HIV-1). Recently, a common variant, SDF1-3‘A, was identified in SDF-1, and an SDF1-3‘A/3‘A homozygous state was shown to delay the onset of acquired immunodeficiency syndrome (AIDS) in an association study involving 2857 patients.¹ The recessive protection of the SDF-1-3‘A allele was pronounced to be twice as effective as the dominant genetic restriction of AIDS conferred by CCR5 and CCR2 chemokine receptor variants.^1-3

Using a polymerase chain reaction–restriction fragment length polymorphism assay, we investigated the distribution of the SDF1-3‘A allele in 16 worldwide representative populations.¹ Our results showed that the SDF1-3‘A allele frequencies vary drastically among the populations surveyed, ranging from 2.9% to 71.4% (Table 1). African populations exhibit the lowest frequencies (2.9%-9.1%), rates that agree with the reported frequency in African Americans.¹ No SDF1-3‘A . . . [Full Text of this Article]