Abstract
BackgroundSusceptibility and resistance to trachoma, the leading infectious cause of blindness, have been associated with a range of host genetic factors. In vitro studies of the causative organism, Chlamydia trachomatis, demonstrate that iron availability regulates its growth, suggesting that host genes involved in regulating iron status and/or availability may modulate the risk of trachoma. The objective was to investigate whether haptoglobin (Hp) haplotypes constructed from the functional polymorphism (Hp1/Hp2) plus the functional promoter SNPs -61A-C (rs5471) and -101C-G (rs5470), or sickle cell trait (HbAS, rs334) were associated with risk of active trachoma when stratified by age and sex, in rural Gambian children.Methodology and Principal FindingsIn two cross sectional surveys of children aged 6–78 months (n = 836), the prevalence of the clinical signs of active trachoma was 21.4%. Within boys, haplotype E (-101G, -61A, Hp1), containing the variant allele of the -101C-G promoter SNP, was associated with a two-fold increased risk of active trachoma (OR = 2.0 [1.17–3.44]). Within girls, an opposite association was non-significant (OR = 0.58 [0.32–1.04]; P = 0.07) and the interaction by sex was statistically significant (P = 0.001). There was no association between trachoma and HbAS.ConclusionsThese data indicate that genetic variation in Hp may affect susceptibility to active trachoma differentially by sex in The Gambia.
Highlights
Trachoma, a chronic keratoconjunctivitis caused by the intracellular bacterium Chlamydia trachomatis, is the leading infectious cause of blindness worldwide [1]
These data indicate that genetic variation in Hp may affect susceptibility to active trachoma differentially by sex in The Gambia
Interventions have considerably reduced the number of people with blinding trachoma over the past decades, current estimates indicate that active trachoma still affects some 80 million people worldwide and about 8 million people are visually impaired [8]
Summary
A chronic keratoconjunctivitis caused by the intracellular bacterium Chlamydia trachomatis, is the leading infectious cause of blindness worldwide [1]. Hp is thought to affect immune regulation, including the balance of Th1:Th2 cytokine responses [35] and several studies have associated haptoglobin phenotypes and genotypes with a range of conditions including cardiovascular disease [36], diabetes [37,38], HIV infection [39,40,41] and susceptibility to malaria [42,43,44,45] including a protective association of the Hp haplotype containing the Hp2 and the C allele for the promoter -61A-C (rs5471) SNP in Gambian children [46]. We investigated whether Hp haplotypes constructed from the functional Hp allele (Hp1 or Hp2) plus the functional promoter SNPs -61A-C (rs5471) and -101C-G (rs5470) and HbAS were associated with the risk of active trachoma in Gambian children
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