Association of a missense mutation of the laminin alpha2 gene with tuberculoid type of leprosy in Indonesian patients

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.

[Leprosy, a pillar of human genetics of infectious diseases]

Despite a natural reservoir of Mycobacterium leprae limited to humans and free availability of an effective antibiotic treatment, more than 200,000 people develop leprosy each year. This disease remains a major cause of disability and social stigma worldwide. The cause of this constant incidence is currently unknown and indicates that important aspects of the complex relationship between the pathogen and its human host remain to be discovered. An important contribution of host genetics to susceptibility to leprosy has long been suggested to account for the considerable variability between individuals sustainably exposed to M. leprae. Given the inability to cultivate M. leprae in vitro and in the absence of relevant animal model, genetic epidemiology is the main strategy used to identify the genes and, consequently, the immunological pathways involved in protective immunity to M. leprae. Recent genome-wide studies have identified new pathophysiological pathways which importance is only beginning to be understood. In addition, the prism of human genetics placed leprosy at the crossroads of other common diseases such as Crohn's disease, asthma or myocardial infarction. Therefore, novel lights on the pathogenesis of many common diseases could eventually emerge from the detailed understanding of a disease of the shadows.

Leprous neuropathy

Leprous neuropathy, which is due to infection of nerve cells by Mycobacterium leprae, still affects millions of people in many developing countries. The clinical and pathological manifestations are determined by the natural resistance of the host to invasion of M. Leprae. Failure of early detection of leprosy often leads to severe disability in spite of eradication of mycobacterium at a later date. In the lepromatous type, bacilli are easily found in the skin and in nerve cells including Schwann cells, endothelial cells, and macrophages. In the tuberculoid type, a strong cell-mediated immune reaction leads to formation of granulomas and destruction of cells harboring bacilli and neighboring nerve fibers. In many cases, treatment of patients with the multibacillary leprosy is complicated by reversal reaction and further nerve damage. Nerve lesions lead to a symmetrical, pseudo-polyneuritic pattern in most cases of lepromatous leprosy, which is usually associated with typical skin lesions, but pure neuritic forms occur in up to 10% of patients with lepromatous leprosy. In the pure neuropathic cases, only nerve biopsy permits diagnosis. The multifocal pattern is more common in tuberculoid leprosy. Treatment is currently based on multidrug therapy with dapsone, rifampicin, and clofazimine. The use of corticosteroids can reduce or prevent nerve damage in reversal reactions. It is important to remember that sequelae, especially sensory loss, are extremely common, which can lead to secondary trophic changes due to repeated trauma in painless areas.

LAMC1 gene is associated with premature ovarian failure

OBJECTIVES

Common variations with modest effect in complex and polygenic disease such as premature ovarian failure (POF) can be detected by a genome wide association study. We performed a genome wide association study to identify predisposing genes associated with an increased risk of POF.

STUDY DESIGN

In stage I, genome wide association study was performed using 24 POF patients and 24 matched controls. A strongly associated region was re-tested to confirm the association with POF in stage II using 98 patients and 218 matched controls.

RESULTS

In the stage I, we found a strongly associated region that was located on chromosome 1q31 and encoded the laminin gamma 1 (LAMC1) gene. All 22 single nucleotide polymorphisms (SNPs) in the LAMC1 formed a linkage disequilibrium block and two haplotypes were significantly associated with POF. In the stage II, 14 SNPs, the majority of which were SNPs located in coding region and tagging SNPs, were genotyped. Distributions of 9 SNPs of them including one nonsynonymous SNP (rs20558) and one haplotype (HT1, C-C-T-G-C-C-A-T-T-C) were significantly higher in POF patients than in control group (86.6% and 74.5%, respectively, OR=2.209, CI: 1.139-4.284, P=0.017).

CONCLUSIONS

We showed for the first time that LAMC1 is significantly associated with POF, and specifically, possession of at least one HT1 was associated with susceptibility to POF. This result means that HT1 may co-exist with causative variant for susceptibility to POF in linkage disequilibrium and that the LAMC1 may be involved in POF pathogenesis.

Leprosy and the human genome

Despite the availability of effective treatment for several decades, leprosy remains an important medical problem in many regions of the world. Infection with Mycobacterium leprae can produce paucibacillary disease, characterized by well-formed granulomas and a Th1 T-cell response, or multibacillary disease, characterized by poorly organized cellular infiltrates and Th2 cytokines. These diametric immune responses confer states of relative resistance or susceptibility to leprosy, respectively, and have well-defined clinical manifestations. As a result, leprosy provides a unique opportunity to dissect the genetic basis of human in vivo immunity. A series of studies over the past 40 years suggests that host genes influence the risk of leprosy acquisition and the predilection for different clinical forms of the disease. However, a comprehensive, cellular, and molecular view of the genes and variants involved is still being assembled. In this article, we review several decades of human genetic studies of leprosy, including a number of recent investigations. We emphasize genetic analyses that are validated by the replication of the same phenotype in independent studies or supported by functional experiments demonstrating biological mechanisms of action for specific polymorphisms. Identifying and functionally exploring the genetic and immunological factors that underlie human susceptibility to leprosy have yielded important insights into M. leprae pathogenesis and are likely to advance our understanding of the immune response to other pathogenic mycobacteria. This knowledge may inform new treatment or vaccine strategies for leprosy or tuberculosis.

Human TLR1 deficiency is associated with impaired mycobacterial signaling and protection from leprosy reversal reaction

Toll-like receptors (TLRs) are important regulators of the innate immune response to pathogens, including Mycobacterium leprae, which is recognized by TLR1/2 heterodimers. We previously identified a transmembrane domain polymorphism, TLR1_T1805G, that encodes an isoleucine to serine substitution and is associated with impaired signaling. We hypothesized that this TLR1 SNP regulates the innate immune response and susceptibility to leprosy. In HEK293 cells transfected with the 1805T or 1805G variant and stimulated with extracts of M. leprae, NF-kappaB activity was impaired in cells with the 1805G polymorphism. We next stimulated PBMCs from individuals with different genotypes for this SNP and found that 1805GG individuals had significantly reduced cytokine responses to both whole irradiated M. leprae and cell wall extracts. To investigate whether TLR1 variation is associated with clinical presentations of leprosy or leprosy immune reactions, we examined 933 Nepalese leprosy patients, including 238 with reversal reaction (RR), an immune reaction characterized by a Th1 T cell cytokine response. We found that the 1805G allele was associated with protection from RR with an odds ratio (OR) of 0.51 (95% CI 0.29-0.87, p = 0.01). Individuals with 1805 genotypes GG or TG also had a reduced risk of RR in comparison to genotype TT with an OR of 0.55 (95% CI 0.31-0.97, p = 0.04). To our knowledge, this is the first association of TLR1 with a Th1-mediated immune response. Our findings suggest that TLR1 deficiency influences adaptive immunity during leprosy infection to affect clinical manifestations such as nerve damage and disability.

Control of human host immunity to mycobacteria

Infection with Mycobacterium tuberculosis results in disease in 5-10% of exposed individuals, whereas the remainder controls infection effectively. Similar inter-individual differences in disease susceptibility are characteristic features of leprosy, typhoid fever, leishmaniasis and other chronic infectious diseases, including viral infections. Although the outcome of infection is influenced by many factors, it is clear that genetic host factors play an important role in controlling disease susceptibility to intracellular pathogens. Knowledge of the genes involved and their downstream cellular pathways will provide new insights for the design of improved and rationalized strategies to enhance host-resistance, e.g. by vaccination. In addition, this knowledge will aid in identifying better biomarkers of protection and disease, which are essential tools for the monitoring of vaccination and other intervention trials. The recent identification of patients with deleterious mutations in genes that encode major proteins in the type-1 cytokine (IL-12/IL23-IFN-gamma) axis, that suffered from severe infections due to otherwise poorly pathogenic mycobacteria (non-tuberculous mycobacteria (NTM) or M. bovis Bacille Calmette-Guerin (BCG)) or Salmonella species has revealed the major role of this system in innate and adaptive immunity to mycobacteria and salmonellae. Clinical tuberculosis has now been described in a number of patients with IL-12/IL23-IFN-gamma system defects. Moreover, unusual mycobacterial infections were reported in several patients with genetic defects in NEMO, a key regulatory molecule in the NFkappaB pathway. These new findings will be discussed since they provide further insights into the role of type-1 cytokines in immunity to mycobacteria, including M. tuberculosis.

Missense mutations of the interleukin-12 receptor beta 1(IL12RB1) and interferon-gamma receptor 1 (IFNGR1) genes are not associated with susceptibility to lepromatous leprosy in Korea

Interleukin-12 receptor beta 1 ( IL12RB1), interleukin-12 receptor beta 2 ( IL12RB2), and interferon gamma receptor 1 ( IFNGR1) perform important roles in the host defense against intracellular pathogens such as Mycobacteria. Several mutations within their genes have been confirmed as associated with increased susceptibility to mycobacterial infection. However, the association between mutations of the IL12RB1, IL12RB2, and IFNGR1 encoding genes and lepromatous leprosy has not been studied. This study screened for polymorphisms within IL12RB1, IL12RB2, and IFNGR1 encoding genes in the Korean populations using polymerase chain reaction (PCR)/single-strand conformation polymorphism (SSCP) DNA sequencing assay, and an association study was performed using the missense mutations of 705 A/G (Q214R), 1196 G/C (G378R), 1637 G/A (A525T), and 1664 C/T (P534S) of the IL12RB1, 83 G/A (V14M), and 1443 T/C (L467P) for the IFNGR1 encoding genes. There were no differences in the genotype and allele frequencies of IL12RB1 and IFNGR1 genes between 93 lepromatous leprosy patients and 94 control subjects. In conclusion, missense mutations of 705 A/G (Q214R), 1196 G/C (G378R), 1637 G/A (A525T), 1664 C/T (P534S) of the IL12RB1, 83 G/A (V14 M), and 1443 T/C (L467P) of the IFNGR1 encoding genes have no association with the susceptibility to lepromatous leprosy in the Korean population.

Defective glycosylation in muscular dystrophy

CONTEXT

Over the past 15 years the causative genes of several inherited muscular dystrophies have been identified. These genes encode sarcolemmal, extracellular matrix, sarcomeric, and nuclear envelope proteins. Although the post-translational processing of muscle proteins has a significant role in their correct assembly and function, these processes have not been shown to be primarily involved in the pathogenesis of muscular dystrophies until recently. In the past 18 months, four different forms of inherited muscular dystrophy in human beings have been associated with mutations in genes encoding for putative glycosyltransferases. Aberrant glycosylation of alpha-dystroglycan, an external membrane protein expressed in muscle, brain, and other tissues, is a common feature in these disorders. alpha-dystroglycan is highly glycosylated, its sugar components varying in different tissues and controlling its interaction with extracellular matrix partners. Disrupted glycosylation of alpha-dystroglycan results in a loss of these interactions, giving rise to both progressive muscle degeneration and abnormal neuronal migration in the brain.

STARTING POINT

Kevin Campbell and colleagues have recently demonstrated that patients with muscle-eye-brain disease (MEB) and Fukuyama congenital muscular dystrophy (FCMD), as well as the myodystrophy (myd) mouse, have an abnormally glycosyated form of alpha-dystroglycan (Nature 2002; 418: 417-22 and 422-25). The abnormally glycosylated protein did not bind to three of its extracellular matrix ligands, laminin alpha2 chain, agrin, and neurexin. The investigators also showed that a neuronal migration disorder occurs in both the myd mouse and in a brain-restricted alpha-dystroglycan knock-out mouse that is similar to that seen in patients with MEB and FCMD. These results identify alpha-dystroglycan as having an essential role in both muscle and brain development and function.

WHERE NEXT

Emphasis is moving away from identifying the protein components of the muscle fibre that are involved in muscular dystrophies towards the post-translational processing of proteins and the enzymes involved in these modifications. This opens up new avenues of research. Abnormal glycosylation of alpha-dystroglycan may underlie other as yet uncharacterised forms of muscular dystrophy and neuronal migration disorders.