MOLECULAR EPIDEMIOLOGY OF MALARIA IN YAOUNDE, CAMEROON - III - ANALYSIS OF CHLOROQUINE RESISTANCE AND POINT MUTATIONS IN THE MULTIDRUG-RESISTANCE-1 (PFMDR 1) GENE OF PLASMODIUM-FALCIPARUM

It has been postulated that chloroquine resistance may be associated w ith a single point mutation at codon 86 of the Plasmodium falciparum m ultidrug resistance 1 (pfmdr 1) gene. Using a simple and rapid molecul ar technique involving polymerase chain reaction and restriction fragm ent length polymorphism, the frequency of the Asn-to-Tyr mutation asso ciated with chloroquine resistance was established among 129 clinical isolates obtained from indigenous patients in Yaounde, Cameroon. The r esults showed that 110 of 129 isolates display a mutant codon. The oth er clinical isolates had either a pure wild-type Asn-86 codon (n = 12) or mixed Asn/Tyr alleles (n = 7). In vitro drug assays were performed to compare the genotype and phenotype in 102 clinical isolates. Of th ese isolates, 86 displayed pure Tyr-86 mutant codon; 48 (56%) mutant i solates were chloroquine-resistant (50% inhibitory concentration [IC50 ] > 100 nM), as expected, but 38 (44%) mutant isolates were chloroquin e-sensitive (IC50 < 100 nM). Three chloroquine-resistant isolates and seven chloroquine-sensitive parasites carried a wild-type Asn-86 codon . Mixed alleles were found in six isolates (four chloroquine-sensitive and two chloroquine-resistant isolates). Our results did not confirm previous observations on the possible association between chloroquine resistance phenotype and genotype based on the pfmdr I gene.