Copy Number Variation of GTP Cyclohydrolase 1 (Gch1) Gene and Its Impact on Antifolate Drug Resistance of Plasmodium Falciparum in Ghana.

Abstract

As part of the malaria control measures in Ghana, sulfadoxine-pyrimethamine (SP) is used as an Intermittent Preventive Treatment (IPTp) among pregnant women and now as a seasonal chemoprophylaxis (SMC) in children on pilot basis. However, parasite resistance to the drug has been reported in the country and this has been linked to point mutations in the dhps (dihydroptoreate synthase) and dhfr (dihydrofolate reductase) genes, the targets of SP. There is also an evidence of amplification of GTP cyclohydrolase 1 (gch1) gene, which codes for the first enzyme in the parasite denovo folate pathway, amongst parasites which harbor the highest SP resistance point mutation (164L) in South East Asia. These point mutations make the parasites less fit, but the acquisition of multiple copies of the gch1 gene may compensate for this fitness cost. This study sought to determine the prevalence and effects of Pfgch1 copy number variations (CNV) on SP resistance amongst clinical isolates in Ghana. Two hundred and two (202) blood samples collected from children aged 14 years and below, with uncomplicated malaria presenting at health centres in Accra, Kintampo, Cape coast, and Navrongo were used in this study. Quantitative real-time PCR (qPCR) and RT qPCR were used to estimate the copy numbers and expression levels respectively. The pfdhps and pfdhfr regions were PCR amplified and directly sequenced. Almost ninety-three percent (92.6%) and 7.4% of the parasite isolates harbored single and double copies of the gch1 gene respectively. Duplication of gch1 gene was independent of the different study sites (P=0.696). Point mutations at dhfr108N (P<0.001) and dhfr108T (P<0.001) were found to be associated with the study sites. Mutations at dhfr108 appear to be fixed in the parasite population and mutations at dhfrS108T and dhpsA581G were observed for the first time in Ghana. However, there were no point mutations observed at codons 164L, 50R and 163T as reported elsewhere. For correlation between the mutations and gch1 CNV, only mutations at dhps540E (P=0.001), and dhps581G (P=0.002) were found to be significant. The relative expression between parasites with gch1 CN of 1 and 2 was about 3-folds. The findings from this study revealed that mutations at dhps540E and dhps581G correlated with double gch1 gene, implying that gch1 may compensate for the fitness cost in parasites harboring these mutations. Continuous monitoring of gch1, dhfr & dhps genes and also further studies to discover component drugs that can inhibit the gch1 gene product are required.