Pfcrt mutant haplotypes may not correspond with chloroquine resistance

Abstract

Introduction: Chloroquine resistance in Plasmodium falciparum is associated with mutations in pfcrt and pfmdr1 genes. The frequency distribution of pfcrt K76T and pfmdr1 N86Y mutations and their association with chloroquine susceptibility was studied in an endemic area along the Indo-Bangladesh border. Methodology: A single-arm prospective study of clinical and parasitological responses in P. falciparum malaria patients to chloroquine was conducted in vivo. PCR-RFLP assay was used to detect pfcrt K76T and pfmdr1 N86Y mutations in P. falciparum. The PCR products of pfcrt gene were sequenced, translated and aligned for haplotyping. Results: Out of 63 cases, 44 (69.8%) responded adequately to chloroquine treatment. Pfcrt K76T mutation was recorded in 100% of the treatment failure cases, whereas pfmdr1 N86Y mutation was found in 52.6% of the cases only. Early treatment failure (84.2%) occurred more frequently than late treatment failure (15.8%). Kaplan-Meier survival analysis showed that the probability estimate for treatment success after 7 and 15 days was 0.84 (95% CI = 0.72-0.92) and 0.70 (95% CI = 0.57-0.80), respectively. Sequence analysis of 72 to 76 pfcrt gene codons revealed the presence of two mutant (CVMNT, CVIET) and two wild (CVMNK, CVIEK) haplotypes. The mutant CVIET haplotype was predominantly distributed (42.1%). Conclusions: The presence of mutations in pfcrt K76T and pfmdr1 N86Y genes is not sufficient to explain the therapeutic efficacy of chloroquine to P. falciparum. Study suggests that pfcrt K76T mutant haplotypes are widely distributed and are spreading diligently, which needs to be taken into account in devising an antimalarial policy.

Return of chloroquine sensitivity to Africa? Surveillance of African Plasmodium falciparum chloroquine resistance through malaria imported to China

“…In addition, one isolate that was wild type at the pfcrt locus had a CQ IC 50 of 124.8 nM, which may indicate the influence of factors other than pfcrt haplotype in CQ resistance, and so warrants further study. In summary, our results indicate a strong association between pfcrt genotype and drug sensitivity, and are consistent with previous studies [ 42 ].…”

Evolution of Fitness Cost-Neutral Mutant PfCRT Conferring P. falciparum 4-Aminoquinoline Drug Resistance Is Accompanied by Altered Parasite Metabolism and Digestive Vacuole Physiology

“…This underscores the notion of K76T as an insufficient predictor of CQR status and supports the fact that CQ resistance or susceptibility can depend on additional PfCRT substitutions (e.g. C101F, L272F, C350R, or in this case A144F), even when K76T is present [22,60–62]. …”

“…We note that parasites encoding Cam734 F144A PfCRT retained K76T as well as 7 other mutations [7]. The clear importance of mutations other than K76T in contributing to CQR can help explain, in areas where novel PfCRT variants have arisen, why the K76T mutation predicts clinical CQR with good sensitivity but only moderate specificity [17,62]. Another important factor driving the reduced specificity of the K76T marker is patient immunity, which in higher-transmission settings of Africa is known to help resolve CQ-resistant infections in CQ-treated patients [78].…”

Molecular Evidence of Increased Resistance to Anti-Folate Drugs in Plasmodium falciparum in North-East India: A Signal for Potential Failure of Artemisinin Plus Sulphadoxine-Pyrimethamine Combination Therapy

“…Earlier studies in north-east India [2], [10] have also reported CQ resistance in more than 80% isolates of Pf indicating non-effectiveness of CQ over the region. Although pfmdr -1 has been thought to affect CQ resistance, however, no correlation between the prevalence of pfcrt mutation and pfmdr -1 point mutation was noted in the present study, which was also observed in earlier studies further strengthening the doubt over its involvement in CQ resistance [32], [33].…”