The X4 phenotype of HIV type 1 evolves from R5 in two children of mothers, carrying X4, and is not linked to transmission
Previously, we found that emergence of the X4 viral phenotype in HIV-1-infected children was related to the presence of X4 in their mothers (C. H. Casper et al., J Infect Dis 2002; 186: 914-921). Here, we investigated the origin of the X4 phenotype in the child, analyzing two mother-child pairs (Ma-Ca, Mb-Cb) where the mothers carried X4 and their children developed X4 after an initial presence of