Finding genetic risk factors for periodontal diseases: is the climb worth the view?

The promise and challenges of genomics-informed periodontal disease diagnoses

Recent advances in human genomics and the advent of molecular medicine have catapulted our ability to characterize human and health and disease. Scientists and healthcare practitioners can now leverage information on genetic variation and gene expression at the tissue or even individual cell level, and an enormous potential exists to refine diagnostic categories, assess risk in unaffected individuals, and optimize disease management among those affected. This review investigates the progress made in the domains of molecular medicine and genomics as they relate to periodontology. The review summarizes the current evidence of association between genomics and periodontal diseases, including the current state of knowledge that approximately a third of the population variance of periodontitis may be attributable to genetic variation and the management of several monogenic forms of the disease can be augmented by knowledge of the underlying genetic cause. Finally, the paper discusses the potential utility of polygenic risk scores and genetic testing for periodontitis diagnosis now and in the future, in light of applications that currently exist in other areas of medicine and healthcare.

Effect of Tumor Necrosis Factor Alpha (TNF-α) -308 and -1031 Gene Polymorphisms on Periodontitis among Saudi Subjects

Objectives

Materials and methods

Results

Conclusion

The association of tumor necrosis factor alpha, lymphotoxin alpha, tumor necrosis factor receptor 1 and tumor necrosis factor receptor 2 gene polymorphisms and serum levels with periodontitis and type 2 diabetes in Serbian population

OBJECTIVES

Aiming to show that periodontitis (PD) and type 2 diabetes (T2D) are bidirectionally related and potentially linked by inflammatory cytokines, we searched for association between -308 G/A Tumor necrosis factor-alpha (TNFα), +252A/G Lymphotoxin-alpha (LTα), +36A/G Tumor necrosis factor receptor 1 (TNFR1) and +676 T/G tumor necrosis factor receptor 2 (TNFR2) single nucleotide polymorphisms (SNPs) and: risk of PD or PD + T2D; periodontitis parameters in PD and PD + T2D; serum levels of cytokines/their receptors. Relationship between periodontal inflammation and serum cytokine/receptor levels was also assessed.

DESIGN

Subjects were stratified as: 57 healthy controls (HC); 58 PD; 65 PD + T2D. Sociodemographic, environmental, behavioral and periodontal clinical data were recorded. SNPs were genotyped using polymerase chain reaction-restriction fragment length polymorphism, while cytokines/receptors levels were quantified by enzyme-linked immunosorbent assay. Impact of periodontal inflammation was measured using periodontal inflamed surface area (PISA).

RESULTS

TNFα AA genotype showed protective effect in T2D + PD compared to PD, even adjusted for behavioral/environmental factors (OR 0.18; 95 %CI 0.037-0.886; p = 0.035). LTα AG heterozygotes had increased risk of PD (OR 3.27; 95 %CI 1.35-7.96; p = 0.016), while TNFR2 TG genotype had protective effect (OR = 0.44; 95 %CI 0.954-0.9794; p = 0.043). TNFR1 AA was predictor of periodontal pocket depth and clinical attachment loss in PD. Correlation between TNFR2 concentration and PISA was negative in PD, positive in PD + T2D.

CONCLUSIONS

None of the SNPs showed cross-susceptibility between PD and T2D. + 252A/G LTα and +676 T/G TNFR2 SNPs are associated with PD risk. Periodontal destruction in healthy individuals is influenced by TNFR1 genotype. Impact of periodontal on systemic inflammation is masked by T2D.

Interleukin-1 Genotype in Periodontitis

This paper presents the current knowledge concerning the role of polymorphisms of IL1A and IL1B genes in periodontitis. Attention has been paid to the role of IL-1 in the pathogenesis of the disease, and to the significance of a genetic test, investigating the presence of composite two polymorphisms of IL-1 gene, as a risk factor for severe periodontitis. The significance of this test for prevention of periodontitis and its therapy has been discussed. IL-1 polymorphisms have been presented and described according to the reference single nucleotide polymorphism (SNP) identification number (rsID), established to eradicate the redundancy of reported polymorphisms in the SNP database processed by the National Center for Biotechnology Information. The prevalence of these genotypes in different populations and ethnic groups and its effect on periodontal health have been discussed. The presented data show inconsistent results. It seems that at least two polymorphisms, rs1800587 and rs1143634, are associated with periodontal inflammation. Therefore, they can be regarded as candidate genes involved in further periodontitis risk assessment. It seems that geographical and ethnical factors can play a great role, as the prevalence of specific polymorphisms varies greatly depending on the population studied.

Association of human leukocyte antigens Class I and Class II antigens with chronic periodontitis in East India

CONTEXT

Human leukocyte antigens (HLAs) have an important role in the determination of susceptibility and resistance to periodontal diseases in humans, which may vary from population to population.

AIMS

The aim of this study was to find out the association of HLA Classes I and II genes with chronic periodontitis in East Indian population.

MATERIALS AND METHODS

In a cross-sectional study design, a total of sixty participants of chronic periodontitis (CP) (mean age: 44.12 ± 5.85) and sixty subjects of periodontal disease-free controls (NP) Periodontitis free controls (mean age 41.85 ± 7.71) were analyzed for their various HLA combinations using serologic (microlymphocytotoxicity test) method. The results are further compared with the HLA profile of 100 samples of blood donors for which periodontal status was unknown. All the data were statistically analyzed by applying Chi-square test.

RESULTS

HLA-B7 (P = 0.003), DR7 (P = 0.001), DR53 (P = 0.001), and DQ3 (P = 0.001) were identified as susceptible phenotypes to CP, whereas HLA-A1 (P = 0.010), A3 (P = 0.001), and Cw4 (P = 0.001) phenotypes were identified to be associated with disease resistance.

CONCLUSION

The HLA-B7, DR7, DR53, and DQ3 alleles may represent as risk factors for CP in Eastern Population of India, whereas HLA-A1, A3, and Cw4 may indicate to protective factors for CP of the same.

Toll-like receptor 9 gene polymorphism in chronic and aggressive periodontitis patients

AIM

Periodontitis is a multifactorial disease, with microbial dental plaque as the primary etiological factor. However, the manifestation and progression of periodontitis is influenced by a wide variety of other determinants and factors such as social and behavioral factors, systemic factors, microbial composition of dental plaque, genetic, and many other emerging risk factors. The aim of this study was to analyze genetic polymorphisms in the toll-like receptor 9 (TLR9) gene at - 1237C/T and its association with chronic and generalized aggressive periodontitis (GAgP) in an Indian population.

MATERIALS AND METHODS

This study was carried out on 90 subjects, which included 30 GAgP and 30 chronic periodontitis patients and 30 healthy controls. Within the limitations of our study, only 30 subjects were included in each group due to the low prevalence of GAgP patients. Blood samples were drawn from the subjects and analyzed for TLR9 genetic polymorphism at - 1237C/T by using polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

No significant difference was found in genotype and allele frequency of TLR9 genetic polymorphism (- 1237C/T) in generalized aggressive and chronic periodontitis patients and healthy controls.

CONCLUSION

Toll-like receptor 9 genetic polymorphism at - 1237C/T may not be associated with GAgP and chronic periodontitis patients in Indian population.

Clinical and subclinical effects of power brushing following experimental induction of biofilm overgrowth in subjects representing a spectrum of periodontal disease

AIM

Investigate short-term effects of power brushing following experimental induction of biofilm overgrowth in periodontal disease states.

MATERIALS AND METHODS

Overall, 175 subjects representing each of five biofilm-gingival interface (BGI) periodontal groups were enrolled in a single-blind, randomized study. After stent-induced biofilm overgrowth for 21 days subjects received either a manual or a power toothbrush to use during a 4 weeks resolution phase. At baseline and during induction and resolution, standard clinical parameters were measured. Subclinical parameters included multikine analysis of 13 salivary biomarkers and 16s Human Oral Microbe Identification Microarray (HOMIM) probe analysis of subgingival plaque samples.

RESULTS

All groups exhibited significantly greater reductions in bleeding on probing (BOP) (p = 0.002), gingival index (GI) (p = 0.0007), pocket depth (PD) (p = 0.04) and plaque index (p = 0.001) with power brushing compared to manual. When BGI groups were combined to form a shallow PD (PD ≤ 3 mm) and a deep PD group (PD > 4 mm) power brushing reduced BOP and GI in subjects with both pocket depths. Power brushing significantly reduced IL-1β levels at resolution while changes in bacterial levels showed non-significant trends between both brushing modalities.

CONCLUSIONS

Short-term changes in select clinical parameters and subclinical salivary biomarkers may be useful in assessing efficacy of power brushing interventions in a spectrum of periodontal disease states.

Expression, polymorphism and methylation pattern of interleukin-6 in periodontal tissues

Periodontitis is considered an inflammatory disorder of bacterial etiology that results in periodontal tissue destruction, as a result of complex interactions between periodontal pathogens, host and immune response. Genetic and epigenetic mechanisms may modulate the individual response since it is able to influence the gene expression. The aim of this study was to evaluate the impact of -174 G/C polymorphism and the methylation status of the promoter region of IL-6 gene on the expression of IL-6 in gingival samples from individuals with chronic periodontitis. Gingival biopsies were collected from 21 patients with chronic periodontitis and 21 controls. Histologic sections stained by hematoxylin-eosin were used for histopathological evaluation. The IL-6 gene expression was assessed by quantitative real-time PCR. The polymorphism IL-6 -174 C/G was studied by polymerase chain reaction (PCR) amplification and restriction endonuclease digestion (HspII). Methylation-specific polymerase chain reaction was used to verify the DNA methylation pattern. The number of inflammatory cells in tissue fragments from individuals with chronic periodontitis was higher than in the control group and the inflammatory infiltrate was predominantly mononuclear. The expression of IL-6 was higher in the group with periodontitis. In polymorphism assay, no statistical difference in the distribution of genotypes and alleles in both groups were observed. The most of samples were partially methylated. No difference was observed in methylation pattern from two different regions of the IL-6 gene among groups. The high expression of IL-6 is an important factor related to chronic periodontitis, but was not associated with methylation status or the -174 (G/C) genetic polymorphism, suggesting that other mechanisms are involved in this gene transcription regulation.

The oral-systemic personalized medicine model at Marshfield Clinic

Periodontal disease and diabetes, two diseases that have achieved epidemic status, share a bidirectional relationship driven by micro-inflammatory processes. The present review frames the current understanding of the pathological processes that appear to link these diseases and advances the hypothesis that reversal of the epidemic is possible through application of interdisciplinary intervention and advancement of oral-systemic personalized medicine. An overview of how Marshfield Clinic's unique clinical, informatics and bio-repository resources and infrastructures are being aligned to advance oral-systemic personalized medicine is presented as an interventional model with the potential to reverse the epidemic trends seen for these two chronic diseases over the past several decades. The overall vision is to engineer a transformational shift in paradigm from 'personalized medicine' to 'personalized health'.

Generalized aggressive periodontitis and its treatment options: case reports and review of the literature

Generalized aggressive periodontitis results in rapid destruction of the periodontium and can lead to early tooth loss in the affected individuals if not diagnosed early and treated appropriately. The diagnostic features of the disease are characteristic, but the clinical presentation and patterns of destructions may vary between patients. Successful management of the disease is challenging especially if diagnosed at advanced stages of the disease, but not impossible with the current therapeutic choices for the disease. A vast array of treatment modalities is available which can be employed in the treatment of generalized aggressive periodontitis with varying success rates, but a definite guideline for the management is yet to be formulated. However, with the exponential rate of developments in periodontal research, regenerative therapy, tissue engineering, and genetic technologies, the future seems promising in regard to options at managing the disease. This paper attempts to describe the clinical and radiographic diagnostic features and the current treatment options along with a suggested protocol for comprehensive management of generalized aggressive periodontitis patients with case reports and a brief review.

Epigenetic regulation of human β-defensin 2 and CC chemokine ligand 20 expression in gingival epithelial cells in response to oral bacteria

Gingival epithelia utilize multiple signaling pathways to regulate innate immune responses to various oral bacteria, but little is understood about how these bacteria alter epithelial epigenetic status. In this study we report that DNA methyltransferase (DNMT1) and histone deacetylase expression were decreased in gingival epithelial cells treated with oral pathogen Porphyromonas gingivalis and nonpathogen Fusobacterium nucleatum. Pretreatment with trichostatin A and sodium butyrate, which increase acetylation of chromatin histones, significantly enhanced the gene expression of antimicrobial proteins human β-defensin 2 (hBD2) and CC chemokine ligand 20 (CCL20) in response to both bacterial challenges. Pretreatment with DNMT inhibitor 5'-azacytidine increased hBD2 and CCL20 expression in response to F. nucleatum, but not to P. gingivalis. Furthermore, we observed a differential pattern of protein levels of H3K4me3, which has been associated with chromatin remodeling and activation of gene transcription, in response to P. gingivalis vs. F. nucleatum. This study provides a new insight into the bacteria-specific innate immune responses via epigenetic regulation.

Single nucleotide polymorphisms of pattern recognition receptors and chronic periodontitis

BACKGROUND AND OBJECTIVE

Periodontitis is a multifactorial disease influenced partly by genetics. Activation of pattern recognition receptors (PRRs) can lead to the up-regulation of inflammatory pathways, resulting in periodontal tissue destruction. Hence, functional polymorphisms located in PRRs can explain differences in host susceptibility to periodontitis. This study investigated single nucleotide polymorphisms of PRRs including toll-like receptor (TLR)2 (G2408A), TLR4 (A896G), TLR9 (T1486C), TLR9 (T1237C) and CD14 (C260T) in patients with chronic periodontitis and in periodontally healthy subjects.

METHODS

One-hundred and fourteen patients with chronic periodontitis and 77 periodontally healthy subjects were genotyped using TaqMan® allelic discrimination assays. Fisher's exact test and chi-square analyses were performed to compare genotype and allele frequencies.

RESULTS

The frequency of subjects with the CC genotype of CD14 (C260T) (24.6% in the chronic periodontitis group vs. 13% in the periodontally healthy group) and those expressing the T allele of CD14 (C260T) (CT and TT) (75.4% in the chronic periodontitis group vs. 87% in the periodontally healthy group) was statistically different among groups (p = 0.04). Homozygocity for the C allele of the CD14 (C260T) polymorphism (CC) was associated with a two--fold increased susceptibility to periodontitis (p = 0.04; odds ratio, 2.49; 95% confidence interval, 1.06-6.26). Individuals with the CC genotype of TLR9 (T1486C) (14.9% in the chronic periodontitis group vs. 28.6% in the periodontally healthy group) and those expressing the T allele of TLR9 (T1486C) (CT and TT) (85.1% in the chronic periodontitis group vs. 71.4% in the periodontally healthy group) were also significantly differently distributed between groups without adjustment (p = 0.03). Further analysis of nonsmokers revealed a significant difference in the distribution of genotypes between groups for TLR9 (T1486C; p = 0.017) and CD14 (C260T; p = 0.03), polymorphisms again without adjustment.

CONCLUSION

The CC genotype of CD14 (C260T) is related to susceptibility to chronic periodontitis in Caucasians. In addition, differences observed in the distribution of TLR9 (T1486C) genotypes between groups warrant further investigation.

Interleukin-8 gene promoter polymorphism (rs4073) may contribute to chronic periodontitis

BACKGROUND

The proinflammatory chemokine interleukin (IL)-8 is important in the regulation of the inflammatory response. Analyses of the single nucleotide polymorphism (SNP) reference sequence (rs) 4073 showed that the A allele upregulated IL-8 levels after stimulation with lipopolysaccharides. We investigated the association of the SNP rs4073 with chronic periodontitis.

METHODS

Genotyping was performed by a standard polymerase chain reaction-restriction fragment length polymorphism assay in 289 genomic DNA samples of healthy control subjects and patients with chronic periodontitis; analyses were adjusted by multivariate logistic regression modeling. A real-time polymerase chain reaction performance was used to detect levels of the IL-8 mRNA.

RESULTS

The analysis pointed to a statistically significant association of chronic periodontitis with the heterozygous TA genotype (P = 0.001); the results showed an increase in the frequency of the A allele in the diseased group (36% in the control group versus 48% in the periodontitis group). The higher levels of the IL-8 mRNA were found in the periodontitis group, mainly in individuals who presented the TA genotype (P = 0.03).

CONCLUSION

The SNP rs4073 was associated with chronic periodontitis in non-smoker Brazilian subjects because the frequency of the A allele was higher in the disease group than in the control group, and the TA genotype was associated with increased levels of IL-8 mRNA transcripts.

Genetic and Environmental Factors in Oral Health among Twins

To date, studies on the contributions of genetic factors to oral health have been inconclusive. We hypothesized that major dental diseases show a significant genetic component. The study was based on self-reported oral health among young adult twins. The data were derived from the fourth wave of the longitudinal FinnTwin16 study, in which participants completed a questionnaire in 2000-2002 enquiring about the number of filled teeth and the prevalence of gingival bleeding. We used quantitative genetic modeling, based on the genetic similarity of identical and non-identical twins, to calculate the most probable model for both filled teeth and gingival bleeding. The models revealed a strong genetic component behind the number of filled teeth, differing between males (49%) and females (68%), and a weaker genetic component affecting gingival bleeding, being similar for males and females (32%). Genetic factors contribute to inter-individual differences in oral health among young adults.

Orofacial findings in chronic granulomatous disease: report of twelve patients and review of the literature

BACKGROUND

Chronic granulomatous disease is an extremely rare primary immunodeficiency syndrome that can be associated with various oral complications. This can affect high number of patients. However, data on oral complications is sparse. Here we will review the literature and describe the orofacial findings in 12 patients.

FINDINGS

The age range was 5-31 years. Oral findings were variable, and reflected a low level of oral hygiene. They included periodontitis, rampant caries, gingivitis, aphthous-like ulcers, and geographic tongue. One patient had white patches on the buccal mucosa similar to lichen planus. Another patient had a nodular dorsum of the tongue associated with fissured and geographic tongue. Biopsies from the latter two lesions revealed chronic non-specific mucositis. Panoramic radiographs showed extensive periodontitis in one patient and periapical lesions in another patient.

CONCLUSION

Patients with chronic granulomatous disease may develop oral lesions reflecting susceptibility to infections and inflammation. It is also possible that social and genetic factors may influence the development of this complication. Therefore, oral hygiene must be kept at an optimum level to prevent infections that can be difficult to manage.

Genetic Risk Factors for Periodontitis in a Japanese Population

Genetic variants at multiple loci have been shown to be associated with susceptibility to periodontitis. To better assess the genetic risk factors for periodontitis, we performed a case-control study in 319 Japanese individuals with periodontitis (172 aggressive and 147 chronic disease) and 303 race-matched healthy control individuals. Thirty-five functional gene polymorphisms that had been previously associated with immune responses were genotyped. For all gene polymorphisms tested, no significant differences were observed in the allele frequencies of persons with aggressive, chronic, and combined (aggressive and chronic) periodontitis, compared with control individuals. Multiple logistic regression analysis revealed a significant association of the vitamin D receptor +1056 T/C polymorphism with susceptibility to chronic periodontitis, after adjustment for age, gender, and smoking status (P = 0.002). These results suggest that none of the polymorphisms tested was strongly associated with periodontitis in a Japanese population. However, the vitamin D receptor +1056 polymorphism may be related to chronic periodontitis.

Rethinking periodontal inflammation

Clinical signs and symptoms, as well as medical and dental history, are all considered in the clinical determination of gingival inflammation and periodontal disease severity. However, the "biologic systems model" highlights that the clinical presentation of periodontal disease is closely tied to the underlying biologic phenotype. We propose that the determination and integration of subject-level factors, microbial composition, systemic immune response, and gingival tissue inflammatory mediator responses will better reflect the biology of the biofilm-gingival interface in a specific patient and may provide insights on clinical management. Disease classifications and multivariable models further refine the biologic basis for the increasing severity of periodontal disease expression. As such, new classifications may better identify disease-susceptible and treatment-non-responsive individuals than current classifications that are heavily influenced by probing and attachment level measurements alone. New data also suggest that the clinical characteristics of some complex diseases, such as periodontal disease, are influenced by the genetic and epigenetic contributions to clinical phenotype. Although the genetic basis for periodontal disease is considered imperative for setting an inflammatory capacity for an individual and, thus, a threshold for severity, there is evidence to suggest an epigenetic component is involved as well. Many factors long associated with periodontitis, including bacterial accumulations, smoking, and diabetes, are known to produce strong epigenetic changes in tissue behavior. We propose that we are now able to rethink periodontal disease in terms of a biologic systems model that may help to establish more homogeneous diagnostic categories and can provide insight into the expected response to treatment.

Complement and c4 null alleles in severe chronic adult periodontitis

Severe forms of chronic periodontitis affect up to 10% of adults. Tumour necrosis factor and lymphotoxin-alpha genes in the major histocompatibility complex are associated with severe periodontitis. Complement factor C4 is a nearby, polymorphic, functionally relevant gene region. Although associated with chronic mucosal infections, C4 deficiencies have not been assessed in adult periodontitis patients. We tested whether complement levels are systemically altered and C4 deficiencies associated with severe chronic periodontitis. In a case-control study, we analysed levels of plasma C3, and C4, serum classical pathway haemolytic activity, C4 allotypes and C4 gene numbers in 37 patients with severe chronic periodontitis and in 150 voluntary controls. Plasma levels of C3 were higher, and classical pathway haemolytic activity was lower in patients than in controls. Partial C4 gene deficiencies were more frequent in patients than in controls (odds ratio 2.4, 95% confidence interval 1.1-5.5, P = 0.032). Changes in complement levels may reflect chronic, recurring inflammation. C4 gene deficiencies are associated with predisposition to chronic periodontitis.

A case-control study on the association of human leukocyte antigen-A*9 and -B*15 alleles with generalized aggressive periodontitis in an Indian population

BACKGROUND

The genes encoding the human leukocyte antigens (HLAs; major histocompatibility complex [MHC]) have been considered candidate markers for periodontitis because they are involved in regulating immune responses. Several studies have examined this association, and despite the inconclusive results, the antigens HLA-A9 and HLA-B15 have been found to be consistently associated with the destructive forms of periodontitis in many populations. Ethnic factors are considered to be a major variable for evaluating the predisposition to the disease. The purpose of the present study was to: 1) assess the association of HLA-A*9 and HLA-B*15 with generalized aggressive periodontitis (GAgP) and 2) evaluate the role of these genetic risk factors in influencing the severity of GAgP in a South Indian population.

METHODS

Forty GAgP patients (cases) and 80 periodontally and systemically healthy subjects (controls) participated in this study. HLA-A*9 and HLA-B*15 typing was carried out using the polymerase chain reaction with sequence specific primers (PCR-SSP)-based molecular method.

RESULTS

HLA-B*15 was a significant risk factor for GAgP and was positively correlated with the disease severity, whereas HLA-A*9 had no association with the disease. The haplotype of HLA-A*9:B*15 did not impart any additional risk for GAgP compared to that imparted by HLA-B*15 alone.

CONCLUSIONS

To our knowledge, this is the first report on HLA-B*15 association with GAgP in an Indian population. The finding of HLA-B*15 as a risk factor may have potential use in the future management of GAgP. The precise disease-causing mechanism of this HLA disease association and whether this association is "causal" or "casual" need to be evaluated further.

Evaluation of RANK/RANKL/OPG gene polymorphisms in aggressive periodontitis

BACKGROUND AND OBJECTIVE

Aggressive periodontitis (AgP) is a specific type of periodontal disease that is characterized by rapid attachment loss and bone destruction. While attempting to identify genetic polymorphisms associated with AgP, previous research has focused on candidate genes that may be involved in immune responses to microbial infections. In this study, the focus was on single nucleotide polymorphisms (SNPs) in the key mediators of osteoclast differentiation and activation, which involve receptor activator of nuclear factor-kappaB (RANK), RANK ligand (RANKL) and osteoprotegrin (OPG), in the Japanese population. The aim of this study was to evaluate the association of RANK/RANKL/OPG gene polymorphisms with AgP in the Japanese population.

MATERIAL AND METHODS

We examined 99 patients with AgP and 89 controls from the Japanese population to explore the possibility of RANK/RANKL/OPG loci as candidate regions associated with the disease. All exons and relevant exon-intron boundaries of these three candidate genes were amplified by polymerase chain reaction (PCR) using 19 primers, followed by direct sequencing. The polymorphisms were identified by comparing the sequences obtained from 48 subjects.

RESULTS

We identified 27 SNPs in RANK, including 10 novel SNPs and seven SNPs each in both RANKL and OPG. A pairwise linkage disequilibrium analysis using the r2 statistic showed that some SNP pairs from the three loci are in tight linkage disequilibrium.

CONCLUSION

An association analysis with allelotypes showed that SNPs identified in the RANK/RANKL/OPG genes have no significant association with AgP in the Japanese population.

CSF1 gene associated with aggressive periodontitis in the Japanese population

Aggressive periodontitis (AgP) is characterized by the early onset of the rapid and progressive destruction of the alveolar bone. We investigated the correlation of single nucleotide polymorphisms (SNPs) in candidate genes with AgP in the Japanese population in order to determine the genetic risk factors for this complex disease. Among 11 genes related to bone formation and resorption, 43 known SNPs were tested in 98 case and 88 control samples for association with AgP by using SNP genotyping techniques. Among these, three polymorphisms located in the colony stimulating factor 1 (CSF1) gene showed a positive association with AgP. This is the first case of an association between a CSF1 polymorphism and a human disease.

Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis subgingival presence, species-specific serum immunoglobulin G antibody levels, and periodontitis disease recurrence

BACKGROUND AND OBJECTIVE

The biological and clinical effects of antibody against periodontal pathogenic bacteria are incompletely understood. This study evaluated the inter-relationships among periodontal levels of cultivable Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis, species-specific serum immunoglobulin G (IgG) antibody levels, and periodontitis disease activity.

MATERIAL AND METHODS

Forty-three adults who had previously been treated for periodontitis and who also harbored cultivable A. actinomycetemcomitans or P. gingivalis were evaluated semiannually for clinical disease recurrence over a 36-month period. Each patient provided subgingival microbial samples, for the recovery of A. actinomycetemcomitans and P. gingivalis, from the two deepest pockets in each dentition sextant. A. actinomycetemcomitans and P. gingivalis serum IgG antibody levels were assessed using enzyme-linked immunosorbent assay (ELISA), together with whole-cell sonicate extracts from A. actinomycetemcomitans serotypes a-c and P. gingivalis ATCC 33277. Data were analyzed using the Mantel-Haenszel chi-square and Fisher exact two-tailed tests.

RESULTS

Eighteen (60.0%) of 30 A. actinomycetemcomitans-positive subjects, and 10 (76.9%) of 13 P. gingivalis-positive subjects, exhibited recurrent periodontal breakdown within 36 months of periodontal therapy. Nineteen (67.9%) of the 28 patients with active periodontitis had A. actinomycetemcomitans or P. gingivalis serum antibody levels below designated threshold values. In comparison, 10 (66.7%) of 15 culture-positive clinically stable subjects showed A. actinomycetemcomitans or P. gingivalis serum antibody levels above threshold values. The difference between specific antibody levels in periodontitis-active and periodontitis-stable patients was statistically significant (p = 0.032).

CONCLUSIONS

Serum levels of IgG antibodies against A. actinomycetemcomitans or P. gingivalis in periodontitis-stable patients were higher than those in patients with active periodontitis. The results suggest that elevated levels of IgG antibody against A. actinomycetemcomitans and P. gingivalis have a detectable protective effect against periodontal infections with these microorganisms.

Analytical epidemiology of periodontitis

AIMS

To review the literature related to the analytical epidemiology of periodontitis generated over the past decade. This review does not deal with descriptive epidemiologic studies of the prevalence, extent and severity of periodontitis with respect to global geography, but focuses exclusively on analytical epidemiology issues, including the challenges posed by the use of different case definitions across studies, current theories and models of disease progression, and risk factors associated with the onset and progression of periodontitis.

METHODS

Relevant publications in the English language were identified after Medline and PubMed database searches.

FINDINGS AND CONCLUSIONS

There is a conspicuous lack of uniformity in the definition of periodontitis used in epidemiologic studies, and findings from different research groups are not readily interpretable. There is a lack of studies that specifically address the distinction between factors responsible for the onset of periodontitis versus those affecting its progression. Colonization by specific bacteria at high levels, smoking, and poorly controlled diabetes have been established as risk factors for periodontitis, while a number of putative factors, including specific gene polymorphisms, have been identified in association studies. There is a clear need for longitudinal prospective studies that address hypotheses emerging from the cross-sectional data and include established risk factors as covariates along with new exposures of interest. Intervention studies, fulfilling the "targeting" step of the risk assessment process, are particularly warranted. Obvious candidates in this context are studies of the efficacy of elimination of specific bacterial species and of smoking cessation interventions as an alternative to the traditional broad anti-plaque approach in the prevention and control of periodontitis. Ideally, such studies should have a randomized-controlled trial design.

Linkage disequilibrium analysis of case-control data: an application to generalized aggressive periodontitis

Several studies have shown a role for the involvement of interleukin (IL)-1 gene cluster polymorphisms in the risk of periodontal diseases. In the present study, we tested polymorphisms, derived from genes of the IL-1 cluster, for association with generalized aggressive periodontitis (GAP) through both allelic association and by constructing a linkage disequilibrium (LD) map of the 2q13-14 disease candidate region. The IL-1RN (VNTR) genotype distribution observed was significantly different in GAP and control subjects (P=0.019). We also observed some evidence for an association between GAP and the IL-1B(+3953) polymorphism (P=0.039). The pattern of association in the region, represented as an LD map, identifies a recombination hot area between the IL-1B(+3953) and IL-1B(-511) polymorphisms. Multilocus modelling of association with disease gives a location for the peak association at the IL-1B(+3953) marker, although support for the peak is not significant. Haplotype analysis identifies a IL-1B(+3953)-IL-1B(-511) haplotype as having the lowest P-value in the region. Recognition of the presence of a recombination hot area between the IL-1B(+3953) and IL-1B(-511) polymorphisms will have an important bearing on future efforts to develop higher resolution SNP analysis in this region for both this and other diseases for which this cluster is implicated.

Real-time polymerase chain reaction quantification of human cytomegalovirus and Epstein-Barr virus in periodontal pockets and the adjacent gingiva of periodontitis lesions

BACKGROUND

Genomic sequences of human cytomegalovirus (HCMV) and Epstein-Barr virus (EBV), two herpesviruses, can frequently be detected in periodontal pockets of progressive periodontitis lesions, but the prevalence and load of the two viruses in gingival tissue are unknown. This study determined levels of HCMV and EBV DNA in the periodontal pocket and in the adjacent gingiva of periodontitis lesions using a real-time polymerase chain reaction (PCR) assay.

MATERIAL AND METHODS

A total of 20 systemically healthy periodontitis patients participated in the study. Nine patients below 35 years of age were tentatively diagnosed as having aggressive (early onset) periodontitis, and 11 patients 36-56 years of age as having chronic (adult) periodontitis. Clinical parameters were evaluated using established methods. Using periodontal curettes, specimens were harvested from 6-10 mm periodontal pockets and from the adjacent inflamed periodontal pocket wall. A 5'-nuclease (TaqMan) real-time PCR assay was used to identify and quantify genomic copies of periodontal HCMV and EBV.

RESULTS

HCMV DNA was detected in 78% of subgingival and 33% of gingival tissue samples from aggressive periodontitis lesions, but only in 46% of subgingival and 9% of gingival tissue samples from chronic periodontitis lesions. In aggressive periodontitis, HCMV subgingival and gingival tissue counts were positively correlated with periodontal pocket depth and probing attachment loss at sample sites (p<or=0.03; Spearman's rank correlation coefficient test). EBV DNA was identified in 89% of subgingival and 78% of gingival tissue samples from aggressive periodontitis lesions, but only in 46% of both subgingival and gingival tissue samples from chronic periodontitis lesions. In aggressive periodontitis, positive correlations were found for EBV subgingival counts and periodontal pocket depth at sample sites (p=0.04; Spearman's correlation) and for EBV gingival tissue counts and whole mouth mean gingival index (p=0.04; Spearman's correlation). In chronic periodontitis, statistical significance was only found between EBV subgingival counts and periodontal pocket depth at sample sites (p=0.04; Spearman's correlation). HCMV-EBV coinfection was revealed in 78% of aggressive periodontitis lesions but only 27% of chronic periodontitis lesions (p=0.03; chi-squared test). Also, seven of nine aggressive periodontitis patients but only three of 11 chronic periodontitis patients revealed more than 10,000 copies of HCMV or EBV in subgingival or gingival tissue samples (p=0.03; chi-squared test). Four of six patients having mean periodontal pocket depth at sample teeth (four study sites per tooth)>6 mm, but none of 14 patients having mean pocket depth at sample teeth<or=6 mm revealed more than 100,000 copies of HCMV or EBV in subgingival or gingival samples (p=0.001; chi-squared test). In periodontitis lesions demonstrating herpesviruses in paired subgingival and gingival tissue samples, the tissue samples showed the higher HCMV copy counts in three of four patients and the higher EBV copy counts in six of eight patients.

CONCLUSIONS

The elevated occurrence of HCMV and EBV DNA copies in periodontal pockets and in the gingival tissue of aggressive periodontitis lesions relative to chronic periodontitis lesions, and the increase in herpesvirus counts with increasing severity of periodontitis lend substantial support to a periodontopathic role of the two viruses. Real-time PCR determination of herpesvirus DNA in periodontal sites may become a promising marker to monitor the course of destructive periodontal disease. Herpesviruses and bacteria, now mostly studied in isolation, may cooperate synergistically in the development of periodontitis, and should probably be considered as a pathogenetic consortium in future investigations of periodontal infections.

Quantitative Measures of Aggressive Periodontitis Show Substantial Heritability and Consistency With Traditional Diagnoses

BACKGROUND

Aggressive periodontitis (AgP) research nearly always classifies subjects into traditional discrete categories of localized or generalized, based upon degree of attachment loss (AL) and types of affected teeth. Since AL is continuous and quantitative, however, useful information is lost. We developed quantitative measures of AgP, compared these to traditional methods, and estimated heritabilities in families.

METHODS

We examined 237 healthy, 169 localized AgP, and 204 generalized AgP subjects. We used the site of maximum AL of each tooth to calculate means for each subject for different groups of teeth. We also applied principal components analysis (PCA) to condense variation among 28 teeth into three orthogonal (uncorrelated) variables. We used discriminant function analysis (DFA) to evaluate how well the quantitative measures match with traditional classifications. Quantitative trait heritabilities were estimated by variance components.

RESULTS

PCA clustered first molars, incisors, and the other teeth into three groups. DFA showed that quantitative measures classified subjects consistent with traditional methods (87% to 94% agreement). Heritabilities ranged from 13.7% (P = 0.10) to 30.0% (P = 0.008) for quantitative measures, with highest values obtained for first molars. A combination of the principal component variables most heavily weighted on first molars and incisors gave the best model of disease susceptibility, with good separation of healthy versus diseased subjects, independent of disease extent or severity.

CONCLUSIONS

Quantitative measures may provide improved precision and power for many kinds of periodontal research. Our finding of significant heritability supports their use in gene mapping studies of AgP susceptibility.

Interleukin-6 (IL-6) − 373 A9T11 allele is associated with reduced susceptibility to chronic periodontitis in Japanese subjects and decreased serum IL-6 level

We investigated whether interleukin-6 (IL-6) gene polymorphisms could be associated with chronic periodontitis (CP) and serum IL-6 level. One hundred and twelve CP and 77 non-CP Japanese subjects were analyzed for IL-6 -597 (G/A), -572 (C/G), -373 (A(n)T(m)), -190 (C/T), and -174 (G/C) polymorphisms. We could only detect -572 and -373 polymorphisms and found that the frequency and carriage rate of the -373 A9T11 allele were significantly higher in non-CP subjects. Enzyme-linked immunosorbent assay confirmed that the -572 and -373 G[A9T11] haplotypes were associated with lower serum IL-6 level. These findings suggest that IL-6 -373 A9T11 allele could be associated with reduced susceptibility to CP among Japanese subjects and decreased serum IL-6 level.

Periodontal epidemiology: towards social science or molecular biology?

Terms such as 'molecular epidemiology' and 'genetic epidemiology' have been coined to depict the change from 'traditional epidemiology', concerned with disease determinants at the community or society level, over to 'modern epidemiology', which is concerned with determinants operating at the individual level or even below, i.e. at the organ, tissue, cell, or molecular level. In this commentary, we point out to the limitations of this development and suggest that more emphasis is placed on making the presumed causal disease models explicit, when investigating the relationship between putative determinants and disease. Understanding the disease processes at the micro-level is insufficient for understanding disease at the individual level; and disease patterns at the population level cannot be understood unless it is realized that individuals exist in a variety of contexts that cannot be reduced to individual attributes.

Association of tumor necrosis factor receptor type 2 +587 gene polymorphism with severe chronic periodontitis

BACKGROUND

Genetic polymorphisms for cytokines and their receptors have been proposed as potential markers for periodontal disease. Tumor necrosis factor receptor 2 (TNFR2) is one of the cell surface receptors for TNF-alpha. Recent studies have suggested that TNFR2 gene polymorphism is involved in autoimmune and other diseases.

OBJECTIVES

The aim of the present study is to evaluate whether TNFR2(+587T/G) gene polymorphism is associated with chronic periodontitis (CP).

METHODS

One hundred and ninety-six unrelated subjects (age 40-65 years) with different levels of CP were identified according to established criteria, including measurements of probing pocket depth (PPD), clinical attachment level (CAL), and alveolar bone loss (BL). All subjects were of Japanese descent and non-smokers. Single nucleotide polymorphism at position +587(T/G) in the TNFR2 gene was detected by a polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) method.

RESULTS

The frequency and the positivity of the +587G allele were significantly higher in severe CP patients than in controls (p=0.0097; odds ratio=2.61, p=0.0075; odds ratio=3.06). In addition, mean values of PPD, CAL, and BL were significantly higher in the +587G allele positive than in the negative subjects (p=0.035, 0.022, and 0.018, respectively).

CONCLUSIONS

These findings suggest that the TNFR2(+587G) polymorphic allele could be associated with severe CP in Japanese.

Evidence of a substantial genetic basis for IgG2 levels in families with aggressive periodontitis

IgG2 is elevated in localized but not in generalized aggressive periodontitis (AgP). Exposure to pathogenic bacteria is essential for disease. Immune responses are dominated by IgG2 reactive with bacterial surface carbohydrates. We used variance component analyses to assess IgG2 heritability and determine whether genes that influence IgG2 are the same genes that influence disease susceptibility. We studied 17 Caucasian and 43 African American families with two or more localized or generalized AgP-affected members (274 subjects with IgG2 measurements). Only 16% of the variance in IgG2 was attributable to age, race, and smoking. Even with the addition of localized AgP, the model still explained only 19% of IgG2 variance. By contrast, heritability of IgG2 levels was estimated to be 38% and highly significant (P = 0.0006), demonstrating a substantial genetic basis. Bi-trait variance component analyses of IgG2 and quantitative measures of AgP indicate that different genes appear to control IgG2 levels and disease susceptibility.