title: Genetic variants associated with non-typhoidal Salmonella bacteraemia in African children.
abstract: BACKGROUND
  Non-typhoidal Salmonella (NTS) causes invasive and frequently fatal disease in African children. Existing strategies to prevent, diagnose, and treat NTS disease are inadequate. An improved understanding of the biology of invasive Salmonella infection will facilitate the development of novel NTS control measures. Despite evidence in mice and man showing a clear role for host genetics in NTS susceptibility, there are no published studies investigating host genetic susceptibility to NTS in African populations.
  
  
  METHODS
  We conducted a genome-wide association study (SNP Array 6.0, Affymetrix, CA, USA) of NTS bacteraemia in Kenyan children, with replication in Malawian children. We assessed the function of NTS-associated variants in an expression quantitative trait locus (eQTL) dataset of interferon γ (IFNγ) and lipopolysaccharide-stimulated monocytes from 432 healthy European adults. Serum IFNγ (Bio-Plex immunoassay, Bio-Rad Laboratories, CA, USA) in Malawian NTS cases (n=106) during acute disease was correlated with genotype by linear regression.
  
  
  RESULTS
  After whole-genome imputation and quality control, 180 Kenyan cases and 2677 controls were included in an association analysis at 7 951 614 (additive model) and 4 669 537 (genotypic model) loci. After quality control, 143 Malawian cases and 336 controls were included in the replication analysis. An intronic variant in STAT4 was associated (recessive model) with NTS in both Kenyan and Malawian children (Kenya p=5·6 × 10(-9), Malawi p=0·02, combined p=1·4 × 10(-9); odds ratio 7·2, 95% CI 3·8-13·5). The NTS-associated variant was an eQTL for STAT4 expression in IFNγ-stimulated monocytes (p=9·59 × 10(-6)), the NTS risk allele being associated with lower STAT4 expression. In Malawian children with NTS bacteraemia, the same NTS risk allele was associated with lower serum concentrations of IFNγ (p=0·02) at presentation.
  
  
  CONCLUSIONS
  STAT4 is highly plausible as a susceptibility locus for invasive NTS disease. STAT4 mediates IFNγ release in T cells and natural killer cells in response to interleukin 12 (IL12). Individuals with rare mutations elsewhere in the IL12-IFNγ axis are at risk of disseminated NTS infection. We provide the first evidence, to our knowledge, of a host genetic determinant of NTS disease in African children, and of a STAT4 variant conferring susceptibility to an infectious disease in man.
  
  
  BACKGROUND
  Wellcome Trust.
authors: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK. Electronic address: james.gilchrist@well.ox.ac.uk.
authors: James J
authors: JJ
authors: Gilchrist
authors: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.
authors: Tara C
authors: TC
authors: Mills
authors: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.
authors: Vivek
authors: V
authors: Naranbhai
authors: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.
authors: Stephen J
authors: SJ
authors: Chapman
authors: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.
authors: Benjamin P
authors: BP
authors: Fairfax
authors: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.
authors: Julian C
authors: JC
authors: Knight
authors: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors: Thomas N
authors: TN
authors: Williams
authors: KEMRI-Wellcome Trust Research Programme, Kilifi, Kenya.
authors: J Anthony G
authors: JA
authors: Scott
authors: MRC Centre for Immune Regulation, School of Immunity and Infection, College of Medicine and Dental Sciences, University of Birmingham, Birmingham, UK.
authors: Calman A
authors: CA
authors: MacLennan
authors: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.
authors: Anna
authors: A
authors: Rautanen
authors: Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK.
authors: Adrian V
authors: AV
authors: Hill