Association of mutations in the Plasmodium falciparum Kelch13 gene (Pf3D7_1343700) with parasite clearance rates after artemisinin-based treatments\u2014a WWARN individual patient data meta-analysis

Wwarn K13 Genotype-Phenotype Study Group

doi:10.1186/s12916-018-1207-3

Abstract

BackgroundPlasmodium falciparum infections with slow parasite clearance following artemisinin-based therapies are widespread in the Greater Mekong Subregion. A molecular marker of the slow clearance phenotype has been identified: single genetic changes within the propeller region of the Kelch13 protein (pfk13; Pf3D7_1343700). Global searches have identified almost 200 different non-synonymous mutant pfk13 genotypes. Most mutations occur at low prevalence and have uncertain functional significance. To characterize the impact of different pfk13 mutations on parasite clearance, we conducted an individual patient data meta-analysis of the associations between parasite clearance half-life (PC1/2) and pfk13 genotype based on a large set of individual patient records from Asia and Africa.MethodsA systematic literature review following the PRISMA protocol was conducted to identify studies published between 2000 and 2017 which included frequent parasite counts and pfk13 genotyping. Four databases (Ovid Medline, PubMed, Ovid Embase, and Web of Science Core Collection) were searched. Eighteen studies (15 from Asia, 2 from Africa, and one multicenter study with sites on both continents) met inclusion criteria and were shared. Associations between the log transformed PC1/2 values and pfk13 genotype were assessed using multivariable regression models with random effects for study site.ResultsBoth the pfk13 genotypes and the PC1/2 were available from 3250 (95%) patients (n = 3012 from Asia (93%), n = 238 from Africa (7%)). Among Asian isolates, all pfk13 propeller region mutant alleles observed in five or more specific isolates were associated with a 1.5- to 2.7-fold longer geometric mean PC1/2 compared to the PC1/2 of wild type isolates (all p ≤ 0.002). In addition, mutant allele E252Q located in the P. falciparum region of pfk13 was associated with 1.5-fold (95%CI 1.4–1.6) longer PC1/2. None of the isolates from four countries in Africa showed a significant difference between the PC1/2 of parasites with or without pfk13 propeller region mutations.Previously, the association of six pfk13 propeller mutant alleles with delayed parasite clearance had been confirmed. This analysis demonstrates that 15 additional pfk13 alleles are associated strongly with the slow-clearing phenotype in Southeast Asia.ConclusionPooled analysis associated 20 pfk13 propeller region mutant alleles with the slow clearance phenotype, including 15 mutations not confirmed previously.

Highlights

Plasmodium falciparum infections with slow parasite clearance following artemisinin-based therapies are widespread in the Greater Mekong Subregion
Of the Asian isolates, nearly half (43%; 1142/ 2631) were from four study sites of the Shoklo Malaria Research Unit (SMRU) along the Western Thailand/Eastern Myanmar Border; these isolates are identified as a group called Thai Western Border
On a more local scale, in this study, we found that the median Parasite clearance half-life (PC1/2) of parasites that already carried a C580Y allele of pfk13 increased from 5.4 h in 2009 to 7.2 h in 2014 in the western border region of Thailand

Summary

Introduction

Studies conducted in 2006–2007 reported that P. falciparum parasites in northwest Cambodia had reduced in vivo susceptibility to artemisinins [1, 2]. This was manifest as delayed clearance of parasites from the blood of patients treated with artesunate monotherapy or ACTs [2]. Mutations in the distinctive propeller region of the Kelch 13 protein (codons 441–726) were associated with slow parasite clearance and subsequently with reduced artemisinin susceptibility in in vitro studies assessing susceptibility of the ring-stage parasites [3, 7, 8]. A central role of pfk propeller mutations in mediating ring-stage resistance was confirmed by demonstration that parasites engineered to contain the mutations showed ring-stage resistance to artemisinin whereas parasites with the wild type allele were sensitive [10]

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