system
Given the following post, respond as if you're commenting on Reddit:
human
Everyone's talking about the fact that babies were genetically modified, but since when did we know there was a gene that prevents HIV? How does it work?
gpt
One way the HIV virus gets into white blood cells is through a protein on the surface of the cell called CCR5. Think of the protein acting as a door through which the virus enters.  Some people have a mutation which alters the size and location of the CCR5 protein, so HIV can no longer get through the "door".  Around 10 percent of Northern Europeans carry one copy of this gene, and around 1 percent carry both copies, making them HIV resistant. This mutation is all but absent from other world regions. Some speculate this may have something to do with epidemics like the Black Death and smallpox that swept through Europe, arguing that the mutation may have provided some sort of advantage against infection by one of these diseases.  Source: learnt about this in a virology class in college, so perhaps this interpretation is a bit basic.