It is not clear what the mechanism of selection has been on the chromosome 6 locus, as analysis of Senegalese samples suggested a potential association with pyrimethamine resistance (Park et al. 2012), but it is unlikely that pyrimethamine caused very strong selection in Guinea, where it has not been officially part of first-line therapy for malaria and no selective signature was seen for the dhfr gene. The gene discussed is DHFR; the disease is malaria.