Candidate Human Genetic Polymorphisms and Severe Malaria in a Tanzanian Population

Alphaxard Manjurano,Eleanor M Riley,Behzad Nadjm,Caroline Maxwell,Raimos Olomi,Hannah Wangai,Susana G Campino,Nuno Sepulveda,Anna Jeffreys,Taane G Clark,Hugh Reyburn,George Mtove,Kirk R Rockett,Christopher Drakeley,Robert Lafrenie

doi:10.1371/journal.pone.0047463

Abstract

Human genetic background strongly influences susceptibility to malaria infection and progression to severe disease and death. Classical genetic studies identified haemoglobinopathies and erythrocyte-associated polymorphisms, as protective against severe disease. High throughput genotyping by mass spectrometry allows multiple single nucleotide polymorphisms (SNPs) to be examined simultaneously. We compared the prevalence of 65 human SNP's, previously associated with altered risk of malaria, between Tanzanian children with and without severe malaria. Five hundred children, aged 1–10 years, with severe malaria were recruited from those admitted to hospital in Muheza, Tanzania and compared with matched controls. Genotyping was performed by Sequenom MassArray, and conventional PCR was used to detect deletions in the alpha-thalassaemia gene. SNPs in two X-linked genes were associated with altered risk of severe malaria in females but not in males: heterozygosity for one or other of two SNPs in the G6PD gene was associated with protection from all forms of severe disease whilst two SNPs in the gene encoding CD40L were associated with respiratory distress. A SNP in the adenyl cyclase 9 (ADCY9) gene was associated with protection from acidosis whilst a polymorphism in the IL-1α gene (IL1A) was associated with an increased risk of acidosis. SNPs in the genes encoding IL-13 and reticulon-3 (RTN3) were associated with increased risk of cerebral malaria. This study confirms previously known genetic associations with protection from severe malaria (HbS, G6PD). It identifies two X-linked genes associated with altered risk of severe malaria in females, identifies mutations in ADCY9, IL1A and CD40L as being associated with altered risk of severe respiratory distress and acidosis, both of which are characterised by high serum lactate levels, and also identifies novel genetic associations with severe malaria (TRIM5) and cerebral malaria(IL-13 and RTN3). Further studies are required to test the generality of these associations and to understand their functional consequences.

Highlights

In spite of recent evidence of successful control in some countries [1,2,3], malaria still constitutes a major cause of child morbidity and mortality, especially in sub Saharan Africa [4,5]
Consistent with the view that severe malaria disease is, at least in part, an inflammatory process mediated by disordered immune responses [14] many of these traits are polymorphisms in genes that are relevant to immunity and inflammation such as the tumor necrosis factor (TNF, MHC class III region, reviewed in [15], Toll-like receptors (TLR-4,9) [16], CD40 ligand (CD40L) [17], the interferon gamma (IFNG), and the Nitric oxide synthase type 2 (NOS2A) genes
Seven single nucleotide polymorphisms (SNPs) were removed from the analysis because they were either monomorphic, deviated from HardyWeinberg equilibrium (HWE) in controls or had high rates (.10%) of missing genotype calls, leaving 58 SNPs which could be analysed for their association with severe malaria

Summary

Introduction

In spite of recent evidence of successful control in some countries [1,2,3], malaria still constitutes a major cause of child morbidity and mortality, especially in sub Saharan Africa [4,5]. The risk factors for severe disease, and the reasons for the wide variation in clinical manifestations of malaria among children who appear to exhibit similar risks for severe disease, are poorly understood. This unexplained variation in disease severity and syndromic phenotype constitutes a major challenge to our understanding of the disease, its treatment and control. In addition to the sickle polymorphism (HbS) [10], G6PD (reviewed in [11]), and ABO blood group [12,13], a number of other traits have been proposed for the reduced risk of severe malaria. Consistent with the view that severe malaria disease is, at least in part, an inflammatory process mediated by disordered immune responses [14] many of these traits are polymorphisms in genes that are relevant to immunity and inflammation such as the tumor necrosis factor (TNF, MHC class III region, reviewed in [15], Toll-like receptors (TLR-4,9) [16], CD40 ligand (CD40L) [17], the interferon gamma (IFNG) (reviewed in [18]), and the Nitric oxide synthase type 2 (NOS2A) genes (reviewed in [19])

Results

Discussion

Conclusion