Frequency of RANTES gene polymorphisms and their association with incidence of malaria: a longitudinal study on children in Iganga district, Uganda

Abstract

Background: The severity and outcome of malaria is influenced by host immunity in which chemokines such as Regulated upon Activation, Normal T cell Expressed and Secreted (RANTES) play an important role. Previous studies show that variations in the RANTES gene affect RANTES protein production, hence altering host immunity. In this study, the relationship between presence of mutations in RANTES and incidence of malaria in a cohort of children living in a malaria-endemic area of Uganda was determined.

Methods: This was a longitudinal study comprising of 423 children aged between 6 months and 9 years, who were actively followed up for 1 year. Malaria episodes occurring in the cohort children were detected and the affected children treated with national policy drug regimen. Mutations in the RANTES gene were determined by PCR-RFLP method and their frequencies were calculated. A multivariate negative binomial regression model was used to estimate the impact of RANTES mutations on malaria incidence. In all statistical tests, a P-value of <0.05 was considered as significant.

Results: The frequencies of the -403A and In1.1C allele were 53.7 and 19.2 %, respectively. No mutations were found at the -28 locus. After adjustment of incidence rates for age, blood group, insecticide-treated bed net (ITN) use, malaria history and the sickle cell trait, 1n1.1T/C heterozygotes and homozygotes showed a non-significant trend towards higher incidence rates compared to wild-type individuals (IRR = 1.10; P = 0.55 and IRR = 1.25; P = 0.60, respectively). Similarly, there was no significant difference in malaria incidence rates between RANTES -403G/A heterozygotes or homozygotes and those without mutations (IRR = 1.09; P = 0.66 and IRR = 1.16; P = 0.50, respectively). No relation was seen between RANTES polymorphisms, baseline parasite densities and the time to first re-infection after administration of anti-malaria drugs.

Conclusions: This study showed that the -403A mutation occurs in nearly half of the study population and the In1.1C allele occurs in one in every four children. Despite the high frequency of these mutations, there was no clear association with malaria incidence. Other studies evaluating more markers, that could potentially modulate RANTES gene transcription alongside other genetic modifiers of malaria susceptibility, may provide further explanations to these less dramatic findings.

Fig. 1

Participant flow chart. Figure showing the 423 children recruited and actively followed-up who provided samples for RANTES gene polymorphisms analysis

Fig. 2

Incidence of malaria among the study participants. 51 % of the study participants had no malaria episodes during the longitudinal follow-up. 5 % experienced 4–9 malaria episodes during the follow-up

Fig. 3

Kaplan–Meier plots for re infection by RANTES INT1.1 genotype (TT, TC or CC). Cumulative re-infections are plotted against weeks to the next infection. The study participants were actively followed-up with visits once every 2 weeks at their homes, to obtain information about re-infection. Using a Cox proportion hazard regression model, adjusting for age, malaria history and ITN use, the predictors of length of time to first re-infection for TT (wild- type); TC (heterozygous) and CC (homozygous) were not statistically different with p-value of 0.28 and 0.67, respectively

Fig. 4

Kaplan–Meier plots for re-infection by RANTES −403 genotype (GG, GA or AA). Cumulative re-infections are plotted against weeks to the next infection. Following an active follow-up with home visits once every 2 weeks, information about re-infection was obtained from the study participants. Using a Cox proportion hazard regression model, adjusting for age, malaria history and ITN use, the predictors of length of time to first re-infection for GG (wild-type); GA (heterozygous) and AA (homozygous) were not statistically different with p-value of 0.21 and 0.42, respectively