Number of amino acids, including deletions, represented at each site within the HVR1. Progressors (cases) are represented in gray; nonprogressors (controls), in black. The mean number of amino acid substitutions per site, including deletions, was 5.3 (SE- 0.54) for the progressors and 5 (SE- 0.61) for nonprogressors (P = .44). Certain sites (2, 6, 7, 23, and 26) were highly conserved for both cases and controls, but other sites (1, 9, 13, 27) had different numbers of substitutions between groups. Sites 2, 4, 9, 13, and 27 had significantly less of the predominant amino acid residue in the case group than in the control group (P =.002, .03, .02, .01, and .02, respectively). For site 2, this was due to one subject's early set of clones with a deletion. For the other sites, this was due to substitutions among several sets of clones.