Segregation of HLA/TNF region is linked to leprosy clinical spectrum in families displaying mixed leprosy subtypes

Pauci- and Multibacillary Leprosy: Two Distinct, Genetically Neglected Diseases

After sustained exposure to Mycobacterium leprae, only a subset of exposed individuals develops clinical leprosy. Moreover, leprosy patients show a wide spectrum of clinical manifestations that extend from the paucibacillary (PB) to the multibacillary (MB) form of the disease. This "polarization" of leprosy has long been a major focus of investigation for immunologists because of the different immune response in these two forms. But while leprosy per se has been shown to be under tight human genetic control, few epidemiological or genetic studies have focused on leprosy subtypes. Using PubMed, we collected available data in English on the epidemiology of leprosy polarization and the possible role of human genetics in its pathophysiology until September 2015. At the genetic level, we assembled a list of 28 genes from the literature that are associated with leprosy subtypes or implicated in the polarization process. Our bibliographical search revealed that improved study designs are needed to identify genes associated with leprosy polarization. Future investigations should not be restricted to a subanalysis of leprosy per se studies but should instead contrast MB to PB individuals. We show the latter approach to be the most powerful design for the identification of genetic polarization determinants. Finally, we bring to light the important resource represented by the nine-banded armadillo model, a unique animal model for leprosy.

Mathematical modelling of leprosy and its control

Leprosy or Hansen's disease is an infectious disease caused by the bacterium Mycobacterium leprae. The annual number of new leprosy cases registered worldwide has remained stable over the past years at over 200,000. Early case finding and multidrug therapy have not been able interrupt transmission completely. Elimination requires innovation in control and sustained commitment. Mathematical models can be used to predict the course of leprosy incidence and the effect of intervention strategies. Two compartmental models and one individual-based model have been described in the literature. Both compartmental models investigate the course of leprosy in populations and the long-term impact of control strategies. The individual-based model focusses on transmission within households and the impact of case finding among contacts of new leprosy patients. Major improvement of these models should result from a better understanding of individual differences in exposure to infection and developing leprosy after exposure. Most relevant are contact heterogeneity, heterogeneity in susceptibility and spatial heterogeneity. Furthermore, the existing models have only been applied to a limited number of countries. Parameterization of the models for other areas, in particular those with high incidence, is essential to support current initiatives for the global elimination of leprosy. Many challenges remain in understanding and dealing with leprosy. The support of mathematical models for understanding leprosy epidemiology and supporting policy decision making remains vital.

Leprosy: an overview of pathophysiology

Leprosy, also known as Hansen's disease, is a chronic infectious disease caused by Mycobacterium leprae, a microorganism that has a predilection for the skin and nerves. The disease is clinically characterized by one or more of the three cardinal signs: hypopigmented or erythematous skin patches with definite loss of sensation, thickened peripheral nerves, and acid-fast bacilli detected on skin smears or biopsy material. M. leprae primarily infects Schwann cells in the peripheral nerves leading to nerve damage and the development of disabilities. Despite reduced prevalence of M. leprae infection in the endemic countries following implementation of multidrug therapy (MDT) program by WHO to treat leprosy, new case detection rates are still high-indicating active transmission. The susceptibility to the mycobacteria and the clinical course of the disease are attributed to the host immune response, which heralds the review of immunopathology of this complex disease.

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.

Leprosy susceptibility: genetic variations regulate innate and adaptive immunity, and disease outcome

The past few years have been very productive concerning the identification of genes associated with leprosy. Candidate gene strategies using both case-control and family-based designs, as well as large-scale approaches such as linkage and gene-expression genomic scans and, more recently, genome-wide association studies, have refined and enriched the list of genes highlighting the most important innate and adaptive immune pathways associated with leprosy susceptibility or resistance. During the early events of host-pathogen interaction identified genes are involved in pattern recognition receptors, and mycobacterial uptake (TLRs, NOD2 and MRC1), which modulate autophagy. Another gene, LTA4H, which regulates the levels of lipoxin A4 and possibly interacts with lipid droplet-related events, also plays a role in the early immune responses to Mycobacterium leprae. Together, the activation of these pathways regulates cellular metabolism upon infection, activating cytokine production through NF-κB and vitamin D-vitamin D receptor pathways, while PARK2 and LRRK2 participate in the regulation of host-cell apoptosis. Concomitantly, genes triggered to form and maintain granulomas (TNF, LTA and IFNG) and genes involved in activating and differentiating T-helper cells (HLA, IL10, as well as the TNF/LTA axis and the IFNG/IL12 axis) bridge immunological regulation towards adaptive immunity. Subtle variations in these genes, mostly single nucleotide polymorphisms, alter the risk of developing the disease or the severity of leprosy. Knowing these genes and their role will ultimately lead to better strategies for leprosy prevention, treatment and early diagnosis. Finally, the same genes associated with leprosy were also associated with autoimmune (Crohn's disease, rheumathoid arthritis, psoriasis) or neurodegenerative diseases (Parkinson's and Alzheimer's). Thus, information retrieved using leprosy as a model could be valuable to understanding the pathogenesis of other complex diseases.

Mycobacterium leprae-host-cell interactions and genetic determinants in leprosy: an overview

Leprosy, also known as Hansen's disease, is a chronic infectious disease caused by Mycobacterium leprae in which susceptibility to the mycobacteria and its clinical manifestations are attributed to the host immune response. Even though leprosy prevalence has decreased dramatically, the high number of new cases indicates active transmission. Owing to its singular features, M. leprae infection is an attractive model for investigating the regulation of human immune responses to pathogen-induced disease. Leprosy is one of the most common causes of nontraumatic peripheral neuropathy worldwide. The proportion of patients with disabilities is affected by the type of leprosy and delay in diagnosis. This article briefly reviews the clinical features as well as the immunopathological mechanisms related to the establishment of the different polar forms of leprosy, the mechanisms related to M. leprae-host cell interactions and prophylaxis and diagnosis of this complex disease. Host genetic factors are summarized and the impact of the development of interventions that prevent, reverse or limit leprosy-related nerve impairments are discussed.

New insights in the pathogenesis and genetics of leprosy

In the last 30 years the leprosy burden has been dramatically reduced but over the last 5 years still more than 200,000 new cases were detected each year. Advances in immunology, pathogenesis, and genetics of leprosy have been reported. A deeper understanding of the mechanisms of infection will ultimately improve our ability to fight against this potentially devastating infectious disease.

Leprosy pathogenetic background: a review and lessons from other mycobacterial diseases

Leprosy is a disease caused by Mycobacterium leprae that initially affects the peripheral nervous system with patients exhibiting contrasting clinical, immunological, and pathological manifestations despite minimal genetic variation among bacilli isolates. Its clinical manifestations are related to M. leprae survival, innate and acquired immune responses, and interactions between host and bacterial proteins, preventing their invasion and infection, or promoting their development and pathogenesis. The complex molecular interactions in affected individuals influenced by the pathogenetic background will be explored in this review. However, the great genetic diversity imposes difficulty for understanding disease development, and it is likely that many factors and metabolic pathways regulating the immense and contrasting symptomatology will yet be revealed. Four pathways may play a central role in leprosy, including the TLR/LIR-7, VDR, TNF-alpha, and TGF-beta1 for which a large amount of gene polymorphisms have been described that could potentially affect the clinical outcome. Cross-talk pathways may significantly change the course of the disease, depending on the specific disequilibrium of genic homeostasis, which is highly dependent on the environment, antigens that are presented to the host cell, and specific polymorphisms that interact with other genes, external factors, and pathogen survival, culminating in leprosy occurrence. Currently, the microarray-based genomic survey of gene polymorphisms, multiple gene expression analyses, and proteomic technologies, such as mass spectrometry and phage display applied in the discovery of antigens, represent a great potential for evaluating individual responses of leprosy patients and contacts to predict the outcome and progression of the disease. At present, none of the genes is good prognostic marker; however, in the near future we may use multiple targets to predict infection and leprosy development.

[Leprosy: a paradigm for the study of human genetic susceptibility to infectious diseases]

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.

Hanseníase: uma doença genética?

A hanseníase é doença infecciosa milenar que, apesar da existência de terapêutica eficaz, ainda persiste como problema de saúde pública em seis países, entre eles o Brasil, líder mundial em prevalência da doença. Ao longo das últimas décadas, a hanseníase vem sendo estudada por perspectiva talvez inesperada para uma doença infecciosa: modernos métodos de análise experimental têm sido empregados para evidenciar a importância do componente genético no controle da susceptibilidade do hospedeiro à hanseníase e seus fenótipos. Esses estudos indicam que constituição genética favorável do hospedeiro, somada a fatores propícios, ambientais e relativos ao agente patogênico, tem alto impacto na definição da susceptibilidade tanto à infecção propriamente dita quanto à evolução clínica da doença. Hoje, diversos genes e regiões genômicas já foram relacionados ao controle da susceptibilidade à hanseníase. Outros estudos estão em andamento, visando ao avanço no entendimento das bases moleculares de controle da susceptibilidade do hospedeiro à doença. O conjunto de resultados desses estudos pode levar a formas mais eficazes de diagnóstico, tratamento e prevenção da hanseníase e outras doenças infecciosas.

Host genetics of mycobacterial diseases in mice and men: forward genetic studies of BCG-osis and tuberculosis

In humans, genetic factors have long been suspected to contribute to the onset and outcome of tuberculosis. Such effects are difficult to identify owing to their complex inheritance, and to the confounding impact of environmental factors, notably pathogen-associated virulence determinants. Recently, forward genetic approaches in mouse models and in human populations have been used to elucidate a molecular basis for predisposition to mycobacterial diseases. The genetic dissection of host predisposition to infection with Mycobacterium bovis BCG and M. tuberculosis will help to define the key molecules involved in host antituberculous immunity and should provide new insights into this important infectious disease.

Age is an important risk factor for onset and sequelae of reversal reactions in Vietnamese patients with leprosy

BACKGROUND

Reversal, or type 1, leprosy reactions (T1Rs) are acute immune episodes that occur in skin and/or nerves and are the leading cause of neurological impairment in patients with leprosy. T1Rs occur mainly in patients with borderline or multibacillary leprosy, but little is known about additional risk factors.

METHODS

We enrolled 337 Vietnamese patients with leprosy in our study, including 169 subjects who presented with T1Rs and 168 subjects with no history of T1Rs. A multivariate analysis was used to determine risk factors for T1R occurrence, time to T1R onset after leprosy diagnosis, and T1R sequelae after treatment.

RESULTS

Prevalence of T1Rs was estimated to be 29.1%. Multivariate analysis identified 3 clinical features of leprosy associated with T1R occurrence. Borderline leprosy subtype (odds ratio, 6.3 [95% confidence interval, 2.9-13.7] vs. polar subtypes) was the major risk factor; 2 other risk factors were positive bacillary index and presence of > 5 skin lesions. In addition, age at leprosy diagnosis was a strong independent risk factor for T1Rs (odds ratio, 2.4 [95% confidence interval, 1.3-4.4] for patients aged > or = 15 years old vs. < 15 years old). We observed that T1Rs with neuritis occurred significantly earlier than pure skin-related T1Rs. Sequelae were present in 45.1% of patients who experienced T1Rs after treatment. The presence of a motor or sensory deficit at T1R onset was an independent risk factor for sequelae, as was the age at diagnosis of leprosy (odds ratio, 4.4 [95% confidence interval, 1.7-11.6] for patients > or = 20 years old vs. < 20 years old).

CONCLUSION

In addition to specific clinical features of leprosy, age is an important risk factor for both T1R occurrence and sequelae after treatment for T1Rs.

Genetic predisposition to leprosy: A major gene reveals novel pathways of immunity to Mycobacterium leprae

The elucidation of the genetic control of susceptibility to common infectious diseases is expected to provide new and more effective tools for prevention and control of some of the most pressings health needs on a global scale. A major advantage of whole genome based genetic approaches is that no a priori assumptions about mechanisms of pathogenesis need to be made in these studies. Hence, genetic studies can identify previously unrecognized pathways of disease susceptibility and tag critical pathogenic events for further biochemical, immunological or physiological analysis. We have applied this strategy to leprosy, a disease that still claims 400,000 new cases each year. We identified genetic variants in the shared promoter region of the PARK2 and PACRG genes as major risk factors of leprosy susceptibility. Both encoded proteins are part of the cellular ubiquitination system. Specifically, PARK2, the cause of early onset Parkinson's disease, is an E3 ligase that likely is involved in controlled proteolysis, the cellular anti-oxidants response and the regulation of innate immune responsiveness. In addition, numerous E3 ligases have recently been shown to be critical regulators of immunity. While the specific role of PARK2/PACRG in leprosy pathogenesis remains unknown, a number of experimentally testable scenarios can be developed to further explore the role of these proteins in anti-Mycobacterium leprae host responsiveness.

Genetic host resistance and susceptibility to leprosy

Leprosy is a chronic infectious disease that affects 600,000 new individuals worldwide every year. This article summarizes some of the advances achieved over the past decades towards the description of the exact number, location and nature of the genetic variants responsible for the well established genetic component controlling leprosy susceptibility in humans.

Genome-wide scans for leprosy and tuberculosis susceptibility genes in Brazilians

Genome-wide scans were conducted for tuberculosis and leprosy per se in Brazil. At stage 1, 405 markers (10 cM map) were typed in 16 (178 individuals) tuberculosis and 21 (173 individuals) leprosy families. Nonparametric multipoint analysis detected 8 and 9 chromosomal regions respectively with provisional evidence (P<0.05) for linkage. At stage 2, 58 markers from positive regions were typed in a second set of 22 (176 individuals) tuberculosis families, with 22 additional markers typed in all families; 42 positive markers in 50 (192 individuals) new leprosy families, and 30 additional markers in all families. Three regions (10q26.13, 11q12.3, 20p12.1) retained suggestive evidence (peak LOD scores 1.31, 1.85, 1.78; P=0.007, 0.0018, 0.0021) for linkage to tuberculosis, 3 regions (6p21.32, 17q22, 20p13) to leprosy (HLA-DQA, 3.23, P=5.8 x 10(-5); D17S1868, 2.38, P=0.0005; D20S889, 1.51, P=0.004). The peak at D20S889 for leprosy is 3.5 Mb distal to that reported at D20S115 for leprosy in India. (151 words).