Human genetics and immune responses are considered to critically influence the outcome of malaria infections including life-threatening syndromes caused by Plasmodium falciparum. An important role in immune regulation is assigned to the apoptosis-signaling cell surface receptor CD95 (Fas, APO-1), encoded by the gene FAS.
Here, a candidate-gene association study including variant discovery at the FAS gene locus was carried out in a case-control group comprising 1,195 pediatric cases of severe falciparum malaria and 769 unaffected controls from a region highly endemic for malaria in Ghana, West Africa. We found the A allele of c.−436C>A (rs9658676) located in the promoter region of FAS to be significantly associated with protection from severe childhood malaria (odds ratio 0.71, 95% confidence interval 0.58–0.88, pempirical = 0.02) and confirmed this finding in a replication group of 1,412 additional severe malaria cases and 2,659 community controls from the same geographic area.
The combined analysis resulted in an odds ratio of 0.71 (95% confidence interval 0.62–0.80, p = 1.8×10−7, n = 6035). The association applied to c.−436AA homozygotes (odds ratio 0.47, 95% confidence interval 0.36–0.60) and to a lesser extent to c.−436AC heterozygotes (odds ratio 0.73, 95% confidence interval 0.63–0.84), and also to all phenotypic subgroups studied, including severe malaria anemia, cerebral malaria, and other malaria complications. Quantitative FACS analyses assessing CD95 surface expression of peripheral blood mononuclear cells of naïve donors showed a significantly higher proportion of CD69+CD95+ cells among persons homozygous for the protective A allele compared to AC heterozygotes and CC homozygotes, indicating a functional role of the associated CD95 variant, possibly in supporting lymphocyte apoptosis.
Severe malaria caused by infection with the protozoan parasite Plasmodium falciparum is a major health burden, causing approximately one million fatalities annually, predominantly among young children in Sub-Saharan Africa. The occurrence of severe malaria may depend on a complex interplay of transmission dynamics and the development of a protective immune response but also on heritable differences in the susceptibility to the disease.
In two large studies including a total of 2,607 affected children and 3,428 apparently healthy individuals from Ghana, West Africa, we investigated genetic variants of the FAS gene, which encodes CD95, a molecule critically involved in the programmed cell death of lymphocytes. We found that a single nucleotide variant in the FAS promoter was associated with a 29%–reduced risk of developing severe malaria. In individuals carrying two copies of the protective allele, a higher proportion of activated lymphocytes was found to express CD95. These findings indicate that a predisposition to an increased expression of CD95 may help to protect from severe malaria, possibly by rendering activated T-lymphocytes more susceptible to programmed cell death.
Citation: Schuldt K, Kretz CC, Timmann C, Sievertsen J, Ehmen C, et al. (2011) A −436C>A Polymorphism in the Human FAS Gene Promoter Associated with Severe Childhood Malaria. PLoS Genet 7(5): e1002066. doi:10.1371/journal.pgen.1002066
Editor: Daniel C. Jeffares, University College London, United Kingdom
Received: November 3, 2010; Accepted: March 18, 2011; Published: May 19, 2011
Copyright: © 2011 Schuldt et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The work was supported by the German National Genome Research Network (NGFN). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Authors: Kathrin Schuldt1,2*, Cosima C. Kretz3, Christian Timmann1,2, Jürgen Sievertsen1, Christa Ehmen1, Claudia Esser1, Wibke Loag4, Daniel Ansong5, Carmen Dering2, Jennifer Evans1, Andreas Ziegler2, Jürgen May4, Peter H. Krammer3, Tsiri Agbenyega5, Rolf D. Horstmann1
1 Department of Molecular Medicine, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany, 2 Institute of Medical Biometry and Statistics, University at Lübeck, University Hospital Schleswig-Holstein, Lübeck, Germany, 3 Division of Immunogenetics, German Cancer Research Centre, Heidelberg, Germany, 4 Infectious Disease Epidemiology Group, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany, 5 School of Medical Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana