Polymorphisms in tumor necrosis factor genes and susceptibility to visceral leishmaniasis in Moroccan children

Human visceral leishmaniasis and polymorphisms in interleukin-coding genes: a systematic review

Visceral leishmaniasis (VL) is a neglected disease that is typical of tropical and subtropical parts of the world and is caused by the trypanosomatid Leishmania donovani complex. This disease is a multifactorial condition that involves parasitic, environmental, and immunogenetic characteristics. Genetic changes in genes encoding cytokines may be associated with changes in their expression and, consequently, with the development of clinical resistance or susceptibility to the disease. This systematic review and meta-analysis aimed to assess whether single nucleotide polymorphisms (SNPs) in interleukin genes influence the clinical consequences of visceral leishmaniasis infection. To this end, we carried out a systematic review and meta-analysis with structured searches in the EMBASE, PubMed, Scopus, SciELO, and Web of Science databases without time restrictions. Two independent reviewers examined the studies, performed data extraction, and assessed quality by assigning scores. If there were any discrepancies, a third reviewer with more experience was consulted. After the screening process, 28 articles were included in the systematic review and 9 in the final analysis of the meta-analysis. Statistical analyses were carried out using various genetic models. The odds ratio (OR) and corresponding 95% confidence intervals (CIs) were calculated to estimate the associations. Overall, the main clinical outcomes were classified as not associated or associated when they presented susceptibility, resistance, risk, or protective factors for the development of the disease. Associations between IFN-γ +874T/A polymorphisms in the dominant model (OR 1.64, 95% CI 1.13-2.38, I2 = 0%, p < 0.01) and heterozygous model (OR 1.72, 95% CI 1.15-2.57, I2 = 0%, p < 0.01) and IL-18 -137G/C in the recessive model (OR 1.33, 95% CI 1.02-1.71, I2 = 9%, p = 0.03) and VL were observed. For the IL-10 gene SNPs, there was no significant association. Our findings suggest that SNPs in the IFN-γ and IL-18 genes may be associated with the risk of developing VL.

Human genetic polymorphism and Leishmaniasis

Leishmaniasis is a disease of the subtropical and tropical spheres of the earth and has various clinical manifestations. The different form of leishmaniasis includes cutaneous leishmaniasis, mucocutaneous leishmaniasis, most lethal visceral leishmaniasis and PKDL form. These different forms depend on many factors such as parasite and vector species, geographical, environmental conditions and population ethnicity. Host genetic factors have been widely investigated for their role in developing the disease in various infections. There are several reports on associations or resistance between candidate gene polymorphisms and the risk and outcome of Leishmania infection. Polymorphism in genes involved in both innate and adaptive immune systems, as well as genes of metabolic processes contributes to disease manifestation. The wide availability and advancement of molecular techniques permits to exploration of hereditary factors related to leishmaniasis. Many candidate gene studies were conducted on family-based and population to identify novel biomarkers for understanding disease pathogenesis pathways and possible drug targets. This comprehensive review presents an update on various human genes polymorphism that influence the outcome of different forms of Leishmania infection in endemic regions of the world. Various electronic databases were searched systematically for relevant publications and thoroughly analyzed. Most of the candidate gene studies were found with discrepancies in findings. Genetic and functional studies with adequate power are needed to validate the contribution of host genes in susceptibility or resistance towards Leishmania infection and understanding pathogenesis.

Meta-analysis of -308G > A polymorphism in TNFα gene and susceptibility to leishmaniasis

The clinical spectrum of leishmaniasis depends on several factors, including Leishmania species and immunogenetic factors. Tumor necrosis factor α (TNFα) plays a central role in immunity against intracellular infections. Many studies have reported that TNFα-308G > A polymorphism is associated with susceptibility to intracellular infections and influences TNFα production. Some studies on the implications of TNFα-308G > A polymorphism in the susceptibility to cutaneous leishmaniasis and visceral leishmaniasis showed controversial results. To draw an overall conclusion using accurate data analysis by increasing the number of cases studied, a meta-analysis was performed based on data from the studies included in the analysis. A total of 1264 patients and 2350 controls were enrolled in the meta-analysis. The results showed no significant association between allele G and allele A of -308G > A polymorphism and leishmaniasis by taking the two subgroups separately [OR_CL = 0.99 (0.84-1.18) and OR_VL = 1.19 (0.88-1.59)] or together [OR = 1.04 (0.90-1.20)]. This meta-analysis insinuates the absence of statistical evidence for an association between allele G and allele A of TNFα-308G > A polymorphism and Leishmania infection outcome. This suggests that TNFα, despite its crucial role in the immune response against Leishmania infection, is not the sole determinant factor. Other factors, such as gene-gene and gene-environment interactions, receptors, and signaling pathway efficiency, may influence TNFα function.