A distinct genotype (designated Dd2-type profile) consisting of 12 point mu
tations and 3 repetitive regions of the CG2 gene, a candidate gene for chlo
roquine resistance, has been associated with in vitro resistance in laborat
ory-adapted strains of Plasmodium falciparum. The DNA sequence of clinical
isolates, characterized by in vitro and in vivo tests, was analyzed to eval
uate whether the genotype corresponds to the phenotype in naturally occurri
ng parasites. Eight of 11 chloroquine-resistant isolates had the Dd2 genoty
pe. One resistant isolate (by in vitro assay) with a sensitive CG2 genotype
was sensitive in vivo. Two resistant isolates and 6 sensitive isolates wer
e multiple infections with mixed alleles, No typical CG2 genotype was found
corresponding to the chloroquine-sensitive isolates. These results suggest
a strong association between the drug-resistant and CG2 genotypes and supp
ort the hypothesis that the CG2 gene may be implicated in chloroquine resis
tance.