Susceptibility to acquiring HIV-1 is a heritable trait, with an in vitro study estimating that 50% is attributable to host genetics.[1,2] However, HIV infection is a gene-by-environment process requiring exposure. It is likely that multiple HIV exposures are required for infection: 100 incidents of sharing needles with an HIV+ injection drug user (IDU) or 200 incidents of unprotected receptive anal sex with an HIV+ partner being needed, on average, to transmit the virus.[3–5] Thus, accounting for HIV exposure is critical to studying host genetics of HIV acquisition.
