Marcelo Távora Mira

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 Parkinsons 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.

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-α (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.

A critical review: an overview of genetic influence on dental caries

Dental decay is a complex, chronic disease and one of the most common illnesses in dentistry today. Several dental decay risk factors have been identified during the last years; however, these variables alone may not entirely explain the disease development. Genetic research applied to dental decay began in the 1930s with experimental reports in animals and human observational research. Only recently, have some studies begun to search for genetic polymorphisms in humans and apply linkage analysis. However, due to the complex characteristics of the disease, the strong influence from several biological and environmental factors, and the small number of genetic studies related to dental caries, the genetic basis still requires further study. Therefore, the aim of this review is to provide a brief description of the current methodology for genetic analysis of complex traits, followed by a comprehensive evaluation of the literature related to genetic susceptibility/resistance to dental decay and a discussion of different aspects of the applied methodology. Advances towards the elucidation of the dental decay genetic basis may contribute to the understanding of the disease etiopathogenesis and to the identification of high risk groups, thus providing potential targets for effective screening, prevention and treatment.

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.

Association between Vitamin D Receptor Gene Polymorphisms and Susceptibility to Chronic Kidney Disease and Periodontitis

Background/Aims: Chronic kidney disease (CKD) and periodontitis (PD) are serious public-health concerns. Vitamin D is a fat-soluble steroid hormone that interacts with its nuclear receptor (VDR) to regulate a variety of biological processes, such as bone metabolism, immune response modulation and transcription of several genes involved in CKD and PD disease mechanisms. The aim of this work was to investigate the association between polymorphisms in the VDR gene and end-stage renal disease (ESRD) and PD. Methods: 222 subjects with and without ESRD (in hemodialysis) were divided into groups with and without PD. Polymorphisms TaqI and BsmI in the VDR gene were analyzed by PCR restriction fragment length polymorphism. The significance of differences in allele, genotype and haplotype frequencies between groups was assessed by the χ2 test (p value <0.05) and odds ratio (OR). Results: Allele G was associated with protection against ESRD: groups without versus with ESRD (GG) × (GA+AA): OR = 2.5, 95% CI = 1.4–4.6, p = 0.00; (G × A): OR = 1.5, 95% CI = 1.0–2.3, p = 0.02; (TG + CG) × (TA + CA): OR = 1.5, 95% CI = 1.0–2.3, p = 0.02. No association was observed between the study polymorphisms and susceptibility to or protection against PD. Conclusion: Allele G of the VDR BsmI polymorphism was associated with protection against ESRD.

Toll-like Receptor 1 N248S Single-Nucleotide Polymorphism Is Associated With Leprosy Risk and Regulates Immune Activation During Mycobacterial Infection

Conflicting findings about the association between leprosy and TLR1 variants N248S and I602S have been reported. Here, we performed case-control and family based studies, followed by replication in 2 case-control populations from Brazil, involving 3162 individuals. Results indicated an association between TLR1 248S and leprosy in the case-control study (SS genotype odds ratio [OR], 1.81; P = .004) and the family based study (z = 2.02; P = .05). This association was consistently replicated in other populations (combined OR, 1.51; P < .001), corroborating the finding that 248S is a susceptibility factor for leprosy. Additionally, we demonstrated that peripheral blood mononuclear cells (PBMCs) carrying 248S produce a lower tumor necrosis factor/interleukin-10 ratio when stimulated with Mycobacterium leprae but not with lipopolysaccharide or PAM3cysK4. The same effect was observed after infection of PBMCs with the Moreau strain of bacillus Calmette-Guerin but not after infection with other strains. Finally, molecular dynamics simulations indicated that the Toll-like receptor 1 structure containing 248S amino acid is different from the structure containing 248N. Our results suggest that TLR1 248S is associated with an increased risk for leprosy, consistent with its hypoimmune regulatory function.

Genetic and immunological evidence implicates interleukin 6 as a susceptibility gene for leprosy type 2 reaction.

In leprosy, type 1 reaction (T1R) and type 2 reaction (T2R) are major causes of nerve injury and permanent disabilities. A previous study on plasma levels of 27 cytokines in patients with T1R or T2R and controls with nonreactional leprosy identified the gene for interleukin 6 (IL-6) as a candidate for genetic analysis. Two nested case-control studies were built from a cohort of 409 patients with leprosy from central Brazil, monitored for T1R and T2R. There was evidence for association between T2R and IL-6 tag single-nucleotide polymorphisms rs2069832 (P = .002), rs2069840 (P = .03), and rs2069845 (P = .04), with information on the entire IL-6 locus, as well as functional IL-6 variant rs1800795 (P = .005). Moreover, IL-6 plasma levels in patients with T2R correlated with IL-6 genotypes (P = .04). No association was found between IL-6 variants and T1R. Identifying genetic predictive factors for leprosy reactions may have a major impact on preventive strategies.

A Major Gene Controls Leprosy Susceptibility in a Hyperendemic Isolated Population from North of Brazil

BACKGROUND Leprosy is a chronic infectious disease that affects 250,000 new individuals/year worldwide. Genetic analysis has been successfully applied to the identification of host genetic factors affecting susceptibility to leprosy; however, a consensus regarding its mode of inheritance is yet to be achieved. METHODS We conducted a complex segregation analysis (CSA) on leprosy using data from the Prata Colony, an isolated, highly endemic former leprosy community located at the outskirts of the Brazilian Amazon. The colony offers large multiplex, multigenerational pedigrees composed mainly by descendents of a small number of original leprosy-affected families. Our enrollment strategy was complete ascertainment leading to the inclusion of the whole colony (2005 individuals, 225 of whom were affected) distributed in 112 pedigrees. CSA was performed using REGRESS software. RESULTS CSA identified a best-fit codominant model, with a major gene accounting for the entire familial effect observed. The frequency of predisposing allele was estimated at 0.22. Penetrance for homozygous individuals for the predisposing allele >30 years old ranged from 56% to 85%, depending on sex. CONCLUSIONS A strong major gene effect in the isolated, hyperendemic Prata Colony indicates enrichment of genetic risk factors, suggesting a population particularly suitable for leprosy gene identification studies.

Leprosy and HIV Coinfection: A Clinical, Pathological, Immunological, and Therapeutic Study of a Cohort from a Brazilian Referral Center for Infectious Diseases

BACKGROUND Although awareness of the relevance of leprosy and human immunodeficiency virus (HIV) coinfection is increasing worldwide, several aspects of this co-occurrence are not fully understood. METHODS We describe clinical, pathological, immunological, and therapeutic long-term follow-up of a cohort of 25 individuals with leprosy and HIV infection from Manaus, Amazonas. RESULTS Careful description of our cohort indicates a higher prevalence of leprosy in an HIV-positive population than that in the general population. We also observed upgrading shifting of leprosy clinical forms after initiation of highly active antiretroviral therapy and multidrug therapy and an impact of HIV infection on leprosy granuloma formation, among other features. CONCLUSION Taken together, these new insights allow the proposition of a classification system that includes (1) leprosy and HIV true coinfection, (2) opportunistic leprosy disease, and (3) leprosy related to highly active antiretroviral therapy.

Genetic Variants of the DDR1 Gene Are Associated with Vitiligo in Two Independent Brazilian Population Samples

Vitiligo is a chronic disease characterized by macules devoid of melanin and identifiable melanocytes. Adhesion of melanocytes to the basement membrane by integrin CCN3 is mediated through collagen IV receptor DDR1. We hypothesize that genetic variants of the DDR1 gene are associated with the occurrence of vitiligo. To test this hypothesis, we genotyped 10 DDR1 tag single-nucleotide polymorphisms (SNPs) in 212 trios composed of an affected child and both parents. Associated markers were then genotyped in 134 independent, unrelated individuals with vitiligo and 134 unrelated controls. Allele T of tag SNP rs4618569 was associated with an increased risk for vitiligo in the family trios (P=0.002, odds ratio (OR)=5.27; 95% confidence interval (CI)=1.59-17.40), whereas allele C of tag SNP rs2267641 was associated with an increased risk for vitiligo in both family-based and case-control populations (P=0.01, OR=3.47; 95% CI=1.22-9.17; P=0.04, OR=6.00; 95% CI=1.73-52.33, respectively). The best evidence for association in the trios was obtained for a haplotype composed of risk alleles of markers rs4618569 and rs2267641 (P=0.0006). There was an age-dependent enrichment of rs4618569 T allele and rs2267641 C allele in early-onset affected individuals. In conclusion, we propose DDR1 as a susceptibility gene for vitiligo, possibly implicating a defective cell adhesion in vitiligo pathogenesis.