CUBN and NEBL common variants in the chromosome 10p13 linkage region are associated with multibacillary leprosy in Vietnam.

Leprosy is caused by infection with Mycobacterium leprae and is classified clinically into paucibacillary (PB) or multibacillary (MB) subtypes based on the number of skin lesions and the bacillary index detected in skin smears. We previously identified a major PB susceptibility locus on chromosome region 10p13 in Vietnamese families by linkage analysis. In the current study, we conducted high-density association mapping of the 9.5 Mb linkage peak on chromosome region 10p13 covering 39 genes. Using leprosy per se and leprosy subtypes as phenotypes, we employed 294 nuclear families (303 leprosy cases, 63 % MB, 37 % PB) as a discovery sample and 192 nuclear families (192 cases, 55 % MB, 45 % PB) as a replication sample. Replicated significant association signals were revealed in the genes for cubilin (CUBN) and nebulette (NEBL). In the combined sample, the C allele (frequency 0.26) at CUBN SNP rs10904831 showed association [p = 1 × 10(-5); OR 0.52 (0.38-0.7)] with MB leprosy only. Likewise, allele T (frequency 0.42) at NEBL SNP rs11012461 showed association [p = 4.2 × 10(-5); OR 2.51 (1.6-4)] with MB leprosy only. These associations remained valid for the CUBN signal when taking into account the effective number of tests performed (type I error significance threshold = 2.4 × 10(-5)). We used the results of our analyses to propose a new model for the genetic control of polarization of clinical leprosy.

Linkage disequilibrium pattern and age-at-diagnosis are critical for replicating genetic associations across ethnic groups in leprosy.

One of the persistent challenges of genetic association studies is the replication of genetic marker-disease associations across ethnic groups. Here, we conducted high-density association mapping of PARK2/PACRG SNPs with leprosy and identified 69 SNPs significantly associated with leprosy in 198 single-case Vietnamese leprosy families. A total of 56 associated SNPs localized to the overlapping promoter regions of PARK2/PACRG. For this region, multivariate analysis identified four SNPs belonging to two major SNP bins (rs1333955, rs7744433) and two single SNP bins (rs2023004, rs6936895) that capture the combined statistical evidence (P = 1.1 × 10(-5)) for association among Vietnamese patients. Next, we enrolled a case-control sample of 364 leprosy cases and 370 controls from Northern India. We genotyped all subjects for 149 SNPs that capture >80 % of the genetic variation in the Vietnamese sample and found 24 SNPs significantly associated with leprosy. Multivariate analysis identified three SNPs (rs1333955, rs9356058 and rs2023004) that capture the association with leprosy (P < 10(-8)). Hence, two SNPs (rs1333955 and rs2023004) were replicated by multivariate analysis between both ethnic groups. Marked differences in the linkage disequilibrium pattern explained some of the differences in univariate analysis between the two ethnic groups. In addition, the strength of association for two promoter region SNP bins was significantly stronger among young leprosy patients in the Vietnamese sample. The same trend was observed in the Indian sample, but due to the higher age-at-diagnosis of the patients the age effect was less pronounced.

Crohn's disease susceptibility genes are associated with leprosy in the Vietnamese population.

A genomewide association study in Chinese patients with leprosy detected association signals in 16 single-nucleotide polymorphisms (SNPs) belonging to 6 loci, of which 4 are related to the NOD2 signaling pathway and are Crohn's disease susceptibility loci. Here, we studied these 16 SNPs as potential leprosy susceptibility factors in 474 Vietnamese leprosy simplex families. We replicated SNPs at HLA-DR-DQ, RIPK2, CCDC122-LACC1, and NOD2 as leprosy susceptibility factors in Vietnam. These results validated the striking overlap in the genetic control of Crohn's disease and leprosy.

TNF -308G>A single nucleotide polymorphism is associated with leprosy among Brazilians: a genetic epidemiology assessment, meta-analysis, and functional study.

Leprosy is an infectious disease caused by Mycobacterium leprae. Tumor necrosis factor (TNF) plays a key role in the host response. Some association studies have implicated the single nucleotide polymorphism TNF -308G>A in leprosy susceptibility, but these results are still controversial. We first conducted 4 association studies (2639 individuals) that showed a protective effect of the -308A allele (odds ratio [OR] = 0.77; P = .005). Next, results of a meta-analysis reinforced this association after inclusion of our new data (OR = 0.74; P = .04). Furthermore, a subgroup analysis including only Brazilian studies suggested that the association is specific to this population (OR = 0.63; P = .005). Finally, functional analyses using whole blood cultures showed that patients carrying the -308A allele produced higher TNF levels after lipopolysaccharide (LPS) (6 hours) and M. leprae (3 hours) stimulation. These results reinforce the association between TNF and leprosy and suggest the -308A allele as a marker of disease resistance, especially among Brazilians.

Human leukocyte antigen class I region single-nucleotide polymorphisms are associated with leprosy susceptibility in Vietnam and India.

Experimental evidence suggested the existence of unidentified leprosy susceptibility loci in the human leukocyte antigen (HLA) complex. To identify such genetic risk factors, a high-density association scan of a 1.9-mega-base (Mb) region in the HLA complex was performed. Among 682 single-nucleotide polymorphisms (SNPs), 59 were associated with leprosy (P <.01) in 198 Vietnamese single-case leprosy families. Genotyping of these SNPs in an independent sample of 292 Vietnamese single-case leprosy families replicated the association of 12 SNPs (P <.01). Multivariate analysis of these 12 SNPs showed that the association information could be captured by 2 intergenic HLA class I region SNPs (P = 9.4 × 10⁻9)-rs2394885 and rs2922997 (marginal multivariate P = 2.1 × 10⁻7 and P = .0016, respectively). SNP rs2394885 tagged the HLA-C*15:05 allele in the Vietnamese population. The identical associations were validated in a third sample of 364 patients with leprosy and 371 control subjects from North India. These results implicated class I alleles in leprosy pathogenesis.

Leprosy as a genetic disease.

Leprosy (Hansen's disease) is a human infectious disease whose etiological agent, Mycobacterium leprae, was identified by G. H. A. Hansen in the 19th century. Despite the high efficacy of multidrug therapy (<0.1% annual relapse rate), transmission is persistent. In 2008, approximately 250,000 new cases were reported to the World Health Organization. Clinically, leprosy presents as either the paucibacillary (1-5 lesions) or the multibacillary (>5 lesions) subtype, highly reflective of a Th1 (cell-mediated) or Th2 (humoral) host immune response, respectively. Subsequent to Mycobacterium leprae exposure, epidemiological studies (e.g., twin studies and complex segregation analyses) maintain the importance of host genetics in susceptibility to leprosy. The results of genome-wide analyses (linkage and association) and candidate gene studies suggest an independent genetic control over both susceptibility to leprosy per se and development of clinical subtype. Moreover, the emergence of a shared genetic background between leprosy and several inflammatory/autoimmune diseases suggests that leprosy is a suitable model for studying the genetic architecture and subsequent pathogenesis of both infectious and inflammatory/autoimmune diseases. We provide the example of NOD2 (Crohn's disease gene) and LTA (myocardial infarction gene) and the implication of a common genetic risk factor between these two diseases and leprosy. The value of leprosy as a model disease therefore extends far beyond this ancient disease to common afflictions of the 21st century.

TNF - 308G>A single nucleotide polymorphism is associated with leprosy among Brazilians: a genetic epidemiology assessment, meta-analysis, and functional study

Leprosy is an infectious disease caused by Mycobacterium leprae. Tumor necrosis factor (TNF) plays a key role in the host response. Some association studies have implicated the single nucleotide polymorphism TNF -308G>A in leprosy susceptibility, but these results are still controversial. We first conducted 4 association studies (2639 individuals) that showed a protective effect of the -308A allele (odds ratio [OR] = 0.77; P = .005). Next, results of a meta-analysis reinforced this association after inclusion of our new data (OR = 0.74; P = .04). Furthermore, a subgroup analysis including only Brazilian studies suggested that the association is specific to this population (OR = 0.63; P = .005). Finally, functional analyses using whole blood cultures showed that patients carrying the -308A allele produced higher TNF levels after lipopolysaccharide (LPS) (6 hours) and M. leprae (3 hours) stimulation. These results reinforce the association between TNF and leprosy and suggest the -308A allele as a marker of disease resistance, especially among Brazilians.

Genetic and functional analysis of common MRC1 exon 7 polymorphisms in leprosy susceptibility.

The chromosomal region 10p13 has been linked to paucibacillary leprosy in two independent studies. The MRC1 gene, encoding the human mannose receptor (MR), is located in the 10p13 region and non-synonymous SNPs in exon 7 of the gene have been suggested as leprosy susceptibility factors. We determined that G396S is the only non-synonymous exon 7-encoded polymorphism in 396 unrelated Vietnamese subjects. This SNP was genotyped in 490 simplex and 90 multiplex leprosy families comprising 704 patients (47% paucibacillary; 53% multibacillary). We observed significant under-transmission of the serine allele of the G396S polymorphism with leprosy per se (P = 0.036) and multibacillary leprosy (P = 0.034). In a sample of 384 Brazilian leprosy cases (51% paucibacillary; 49% multibacillary) and 399 healthy controls, we observed significant association of the glycine allele of the G396S polymorphism with leprosy per se (P = 0.016) and multibacillary leprosy (P = 0.023). In addition, we observed a significant association of exon 7 encoded amino acid haplotypes with leprosy per se (P = 0.012) and multibacillary leprosy (P = 0.004). Next, we tested HEK293 cells over-expressing MR constructs (293-MR) with three exon 7 haplotypes of MRC1 for their ability to bind and internalize ovalbumin and zymosan, two classical MR ligands. No difference in uptake was measured between the variants. In addition, 293-MR failed to bind and internalize viable Mycobacterium leprae and BCG. We propose that the MR-M. leprae interaction is modulated by an accessory host molecule of unknown identity.

[Leprosy: a paradigm for the study of human genetic susceptibility to infectious diseases]. / La lèpre: un paradigme pour l'étude de la prédisposition génétique aux maladies infectieuses.

Fifty years ago, the first identification of a non Mendelian genetic contribution to the development of a common infectious disease, i.e. the association between malaria and sickle-cell trait, was shown using a supervised approach which tests a limited number of candidate genes selected by hypothesis. Since then, the few genes that were convincingly associated with susceptibility to human infectious diseases were identified following the same strategy. The study of leprosy has contributed to modifying this way of thinking. In the absence of a satisfying experimental model and because of the impossibility to grow the causative agent in vitro, the candidate gene approach has turned out to be of limited interest. Conversely, positional cloning led to the identification of two major genes involved in the control of the disease, establishing for the first time the oligogenic nature of a human genetic contribution to an infectious disease. It is likely that these major results obtained in leprosy and the recent burst of genomic tools will make the genome-wide screening (functional or positional) the main strategy of dissection of the genetic susceptibility to many common infectious diseases.

Leprosy as a genetic model for susceptibility to common infectious diseases.

Leprosy (Hansen's disease) is a human infectious disease that can be effectively treated with long-term administration of multi-drug therapy. In 2006, over 250,000 new cases were reported to the World Health Organization. In the nineteenth century, disagreement among leprologists regarding the hereditary or infectious nature of leprosy was resolved with the identification of the etiological agent, Mycobacterium leprae. However, epidemiological studies maintain the importance of host genetics in leprosy susceptibility. A model free genome-wide linkage scan in multi-case families from Vietnam led to the positional cloning of global genetic risk factors in the PARK2/PACRG and LTA genes. The process of identifying the susceptibility variants provided invaluable insight into the replication of genetic effects, particularly the importance of considering population-specific linkage-disequilibrium structure. As such, these studies serve to improve our understanding of leprosy pathogenesis by implicating novel biological pathways while simultaneously providing a genetic model for common infectious diseases.

Genomewide linkage analysis of the granulomatous mitsuda reaction implicates chromosomal regions 2q35 and 17q21.

The Mitsuda reaction, a delayed granulomatous skin reaction elicited by the intradermal injection of heat-killed Mycobacterium leprae, is an in vivo test reflecting the ability to generate an immune granuloma after sensitization by diverse mycobacterial infections. Accumulating evidence for the genetic control of the Mitsuda reaction has been reported. We performed a genomewide linkage scan for the quantitative Mitsuda reaction in 19 large families from Vietnam with a history of leprosy (114 offspring). Suggestive linkage was found at chromosomal regions 2q35 (P = 9 x 10(-4) at the SLC11A1 locus) and 17q21-25 (P = 8 x 10(-4)). Interestingly, these 2 regions have been previously linked to mycobacterial infection and other granulomatous diseases.

Stepwise replication identifies a low-producing lymphotoxin-alpha allele as a major risk factor for early-onset leprosy.

Host genetics has an important role in leprosy, and variants in the shared promoter region of PARK2 and PACRG were the first major susceptibility factors identified by positional cloning. Here we report the linkage disequilibrium mapping of the second linkage peak of our previous genome-wide scan, located close to the HLA complex. In both a Vietnamese familial sample and an Indian case-control sample, the low-producing lymphotoxin-alpha (LTA)+80 A allele was significantly associated with an increase in leprosy risk (P = 0.007 and P = 0.01, respectively). Analysis of an additional case-control sample from Brazil and an additional familial sample from Vietnam showed that the LTA+80 effect was much stronger in young individuals. In the combined sample of 298 Vietnamese familial trios, the odds ratio of leprosy for LTA+80 AA/AC versus CC subjects was 2.11 (P = 0.000024), which increased to 5.63 (P = 0.0000004) in the subsample of 121 trios of affected individuals diagnosed before 16 years of age. In addition to identifying LTA as a major gene associated with early-onset leprosy, our study highlights the critical role of case- and population-specific factors in the dissection of susceptibility variants in complex diseases.

Quantifying genomic imprinting in the presence of linkage.

Genomic imprinting decreases the power of classical linkage analysis, in which paternal and maternal transmissions of marker alleles are equally weighted. Several methods have been proposed for taking genomic imprinting into account in the model-free linkage analysis of binary traits. However, none of these methods are suitable for the formal identification and quantification of genomic imprinting in the presence of linkage. In addition, the available methods are designed for use with pure sib-pairs, requiring artificial decomposition in cases of larger sibships, leading to a loss of power. We propose here the maximum likelihood binomial method adaptive for imprinting (MLB-I), which is a unified analytic framework giving rise to specific tests in sibships of any size for (i) linkage adaptive to imprinting, (ii) genomic imprinting in the presence of linkage, and (iii) partial versus complete genomic imprinting. In addition, we propose an original measure for quantifying genomic imprinting. We have derived and validated the distribution of the three tests under their respective null hypotheses for various genetic models, and have assessed the power of these tests in simulations. This method can readily be applied to genome-wide scanning, as illustrated here for leprosy sibships. Our approach provides a novel tool for dissecting genomic imprinting in model-free linkage analysis, and will be of considerable value for identifying and evaluating the contribution of imprinted genes to complex diseases.

Susceptibility to leprosy is associated with PARK2 and PACRG.

Leprosy is caused by Mycobacterium leprae and affects about 700,000 individuals each year. It has long been thought that leprosy has a strong genetic component, and recently we mapped a leprosy susceptibility locus to chromosome 6 region q25-q26 (ref. 3). Here we investigate this region further by using a systematic association scan of the chromosomal interval most likely to harbour this leprosy susceptibility locus. In 197 Vietnamese families we found a significant association between leprosy and 17 markers located in a block of approx. 80 kilobases overlapping the 5' regulatory region shared by the Parkinson's disease gene PARK2 and the co-regulated gene PACRG. Possession of as few as two of the 17 risk alleles was highly predictive of leprosy. This was confirmed in a sample of 975 unrelated leprosy cases and controls from Brazil in whom the same alleles were strongly associated with leprosy. Variants in the regulatory region shared by PARK2 and PACRG therefore act as common risk factors for leprosy.