HLA Class II Locus and Susceptibility to Podoconiosis

Center for Research on Genomics and Global Health, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892-5635, USA.
New England Journal of Medicine (Impact Factor: 55.87). 03/2012; 366(13):1200-8. DOI: 10.1056/NEJMoa1108448
Source: PubMed

ABSTRACT Podoconiosis is a tropical lymphedema resulting from long-term barefoot exposure to red-clay soil derived from volcanic rock. The World Health Organization recently designated it as a neglected tropical disease. Podoconiosis develops in only a subgroup of exposed people, and studies have shown familial clustering with high heritability (63%).
We conducted a genomewide association study of 194 case patients and 203 controls from southern Ethiopia. Findings were validated by means of family-based association testing in 202 family trios and HLA typing in 94 case patients and 94 controls.
We found a genomewide significant association of podoconiosis with the single-nucleotide polymorphism (SNP) rs17612858, located 5.8 kb from the HLA-DQA1 locus (in the allelic model: odds ratio, 2.44; 95% confidence interval [CI], 1.82 to 3.26; P=1.42×10(-9); and in the additive model: odds ratio, 2.19; 95% CI, 1.66 to 2.90; P=3.44×10(-8)), and suggestive associations (P<1.0×10(-5)) with seven other SNPs in or near HLA-DQB1, HLA-DQA1, and HLA-DRB1. We confirmed these associations using family-based association testing. HLA typing showed the alleles HLA-DRB1*0701 (odds ratio, 2.00), DQA1*0201 (odds ratio, 1.91), and DQB1*0202 (odds ratio, 1.79) and the HLA-DRB1*0701-DQB1*0202 haplotype (odds ratio, 1.92) were risk variants for podoconiosis.
Association between variants in HLA class II loci with podoconiosis (a noncommunicable disease) suggests that the condition may be a T-cell-mediated inflammatory disease and is a model for gene-environment interactions that may be relevant to other complex genetic disorders. (Funded by the Wellcome Trust and others.).

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Available from: Elena Hailu, Sep 29, 2015
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    • "The regression residuals indicate that the development of podoconiosis depends on etiological factors other than purely environmental factors. Genetic susceptibility has been shown to be another key aetiological factor [37], as have shoe-wearing practices [37,38]. This study had limited capability to capture individual behaviours, disease severity and genetic variations in relation with environmental factors that are also likely to have been important factors in explaining the residual variation [39,40]. "
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    ABSTRACT: Introduction The precise trigger of podoconiosis — endemic non-filarial elephantiasis of the lower legs — is unknown. Epidemiological and ecological studies have linked the disease with barefoot exposure to red clay soils of volcanic origin. Histopathology investigations have demonstrated that silicon, aluminium, magnesium and iron are present in the lower limb lymph node macrophages of both patients and non-patients living barefoot on these clays. We studied the spatial variation (variations across an area) in podoconiosis prevalence and the associated environmental factors with a goal to better understanding the pathogenesis of podoconiosis. Methods Fieldwork was conducted from June 2011 to February 2013 in 12 kebeles (administrative units) in northern Ethiopia. Geo-located prevalence data and soil samples were collected and analysed along with secondary geological, topographic, meteorological and elevation data. Soil data were analysed for chemical composition, mineralogy and particle size, and were interpolated to provide spatially continuous information. Exploratory, spatial, univariate and multivariate regression analyses of podoconiosis prevalence were conducted in relation to primary (soil) and secondary (elevation, precipitation, and geology) covariates. Results Podoconiosis distribution showed spatial correlation with variation in elevation and precipitation. Exploratory analysis identified that phyllosilicate minerals, particularly clay (smectite and kaolinite) and mica groups, quartz (crystalline silica), iron oxide, and zirconium were associated with podoconiosis prevalence. The final multivariate model showed that the quantities of smectite (RR = 2.76, 95% CI: 1.35, 5.73; p = 0.007), quartz (RR = 1.16, 95% CI: 1.06, 1.26; p = 0.001) and mica (RR = 1.09, 95% CI: 1.05, 1.13; p < 0.001) in the soil had positive associations with podoconiosis prevalence. Conclusions More quantities of smectite, mica and quartz within the soil were associated with podoconiosis prevalence. Together with previous work indicating that these minerals may influence water absorption, potentiate infection and be toxic to human cells, the present findings suggest that these particles may play a role in the pathogenesis of podoconiosis and acute adenolymphangitis, a common cause of morbidity in podoconiosis patients.
    International Journal of Health Geographics 06/2014; 13(1):24. DOI:10.1186/1476-072X-13-24 · 2.62 Impact Factor
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    • "It often affects barefoot subsistence farmers exposed to irritant volcanic soils [1]. Current evidence also suggests genetic susceptibility [1,2]. Podoconiosis is found across Asia, South America, and tropical Africa including Ethiopia where an estimated one million people are affected. "
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    ABSTRACT: Podoconiosis, or non-filarial elephantiasis, is a neglected tropical disease (NTD) characterised by swelling of the lower legs. When left untreated, this disfiguring condition has a significant social impact. This study aimed to describe the stigma experience among podoconiosis patients in Dembecha, Northern Ethiopia and assess potential associations between stigma and sociodemographic determinants. The study was conducted in May 2012 in Northern Ethiopia. A questionnaire-based cross-sectional study design was used and stigma was assessed using a validated podoconiosis stigma scale including 'felt' and 'enacted' stigma domains. Enacted stigma includes the experience of discrimination such as abuse, loss of employment or prejudicial attitudes, while felt stigma is the perceived fear of enacted stigma. A multivariable linear regression model was used to explore determinants that may be associated with stigma. A total of 346 clinically confirmed podoconiosis patients participated in the study. The total mean score of all stigma scale items was 30.7 (Range = 0 to 96). There was a higher mean score of scale items in domains of felt stigma (21.7; Range = 0 to 45) as compared to enacted stigma (9.0; Range = 0 to 51). The total mean score of all stigma scale items appeared to increase with disease stage. A final adjusted linear regression model found an association between stigma and factors including monthly income, duration lived in the current residence, and disease stage, after controlling for confounders. Podoconiosis is a stigmatized disease with a clear social impact. This paper documented the burden of podoconiosis-related stigma and identified associated factors. Programs aimed at preventing and treating podoconiosis should incorporate interventions to mitigate both felt and enacted stigma. Interventions targeting patients should prioritize those with advanced disease.
    BMC Public Health 12/2013; 13(1):1178. DOI:10.1186/1471-2458-13-1178 · 2.26 Impact Factor
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    • "Recently, family-based association study using GWAS was conducted to elucidate the genetic underpinnings of podoconiosis. This study, focused on continental African population groups, found genetic susceptibility to podoconiosis [60]. In addition to identifying genes associated with NCDs such as podoconisosis, GWAS has been used to identify treatment outcomes based on genotypes for NCDs. "
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    ABSTRACT: Traditionally, biomedical research endeavors in low to middle resources countries have focused on communicable diseases. However, data collected over the past 20 years by the World Health Organization (WHO) show a significant increase in the number of people suffering from non-communicable diseases (e.g. heart disease, diabetes, cancer and pulmonary diseases). Within the coming years, WHO predicts significant decreases in communicable diseases while non-communicable diseases are expected to double in low and middle income countries in sub-Saharan Africa. The predicted increase in the non-communicable diseases population could be economically burdensome for the basic healthcare infrastructure of countries that lack resources to address this emerging disease burden. Biomedical research could stimulate development of healthcare and biomedical infrastructure. If this development is sustainable, it provides an opportunity to alleviate the burden of both communicable and non-communicable diseases through diagnosis, prevention and treatment. In this paper, we discuss how research using biomedical technology, especially genomics, has produced data that enhances the understanding and treatment of both communicable and non-communicable diseases in sub-Saharan Africa. We further discuss how scientific development can provide opportunities to pursue research areas responsive to the African populations. We limit our discussion to biomedical research in the areas of genomics due to its substantial impact on the scientific community in recent years however, we also recognize that targeted investments in other scientific disciplines could also foster further development in African countries.
    Globalization and Health 10/2013; 9(1):50. DOI:10.1186/1744-8603-9-50 · 2.25 Impact Factor
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