Improved evidence for linkage on 6p and 5p with retrospective pooling of data from three asthma genome screens

Contribution of allergic inflammatory response to the pathogenesis of malaria disease

Plasmodium falciparum, the aetiological agent of human lethal malaria, is responsible for over 2 million deaths per year and malaria episodes may vary considerably in their severity and clinical manifestations. Dysregulated balance of the inflammatory response and a defect in the anti-Plasmodium parasite immune response represent the hallmarks of malaria disease. Among the many possible mechanisms, it is now widely recognized that the production of pro-inflammatory mediators and cytokines and upregulation of endothelial cell adhesion molecules play important roles in malaria pathogenesis. We and others provided evidence that some components of allergic inflammatory response to malaria parasites or elicited by by-products of parasite infection may contribute to malaria pathogenesis. This review provides some clue regarding these mechanisms where mast cells and histamine, an inflammatory mediator generated following IgE-independent or IgE-mediated immune response, were found to play a major role in parasite transmission and malaria pathogenesis, respectively. This article is part of a Special Issue entitled: Mast cells in inflammation.

Genetic determination and linkage mapping of Plasmodium falciparum malaria related traits in Senegal

Plasmodium falciparum malaria episodes may vary considerably in their severity and clinical manifestations. There is good evidence that host genetic factors contribute to this variability. To date, most genetic studies aiming at the identification of these genes have used a case/control study design for severe malaria, exploring specific candidate genes. Here, we performed a family-based genetic study of falciparum malaria related phenotypes in two independent longitudinal survey cohorts, as a first step towards the identification of genes and mechanisms involved in the outcome of infection. We studied two Senegalese villages, Dielmo and Ndiop that differ in ethnicity, malaria transmission and endemicity. We performed genome-scan linkage analysis of several malaria-related phenotypes both during clinical attacks and asymptomatic infection. We show evidence for a strong genetic contribution to both the number of clinical falciparum malaria attacks and the asymptomatic parasite density. The asymptomatic parasite density showed linkage to chromosome 5q31 (LOD = 2.26, empirical p = 0.0014, Dielmo), confirming previous findings in other studies. Suggestive linkage values were also obtained at three additional chromosome regions: the number of clinical malaria attacks on chromosome 5p15 (LOD = 2.57, empirical p = 0.001, Dielmo) and 13q13 (LOD = 2.37, empirical p = 0.0014 Dielmo), and the maximum parasite density during asymptomatic infection on chromosome 12q21 (LOD = 3.1, empirical p<10⁻⁴, Ndiop). While regions of linkage show little overlap with genes known to be involved in severe malaria, the four regions appear to overlap with regions linked to asthma or atopy related traits, suggesting that common immune related pathways may be involved.

Genetic predisposition to asthma and atopy

A large number of studies have tried to identify heritable components in the susceptibility to asthma and atopy phenotypes. This review examines the evidence of multigenetic inheritance for these conditions. We identified in the literature at least 372 gene-disease association studies for asthma and 124 for atopy published in the last 6 years. Gene-environment analyses were performed in 41 and 14 articles, respectively, in the same time period. Many postulated associations have been probed with limited sample sizes and will require more extensive replication and large-scale evidence. Meta-analyses have been performed for polymorphisms in 5 genes and provide modest evidence for genetic association of asthma with ADAM33 and TNFA gene polymorphisms. Meta-analyses of linkage studies show that it is unlikely to detect strong linkage peaks for asthma susceptibility. However, linkage was claimed between loci on chromosomes 2, 4, 6, 9, 10, 11 and 15 and total serum IgE levels. Careful definitions and standardization of phenotypes across teams of investigators are important to endorse. New large-scale testing platforms may offer new opportunities for discovering susceptibility gene variants, but they need to be coupled with careful study design, international collaboration, and possibly also dissection of gene-environment interactions.