way to the cell surface. Without CCR5 proteins to attach to, HIV molecules can’t infect the cells. In people of African and Asian descent, the thirty-two-letter CCR5 deletion is virtually nonexistent, but it’s fairly prevalent among Caucasian people; 10 to 20 percent of Caucasians possess one copy of the mutated gene, and homozygous individuals—those who possess two copies—are completely resistant to HIV. Roughly 1 to 2 percent of Caucasians worldwide (most of them in northeastern Europe) are fortunate enough to have this trait. These CCR5-lacking
