Perio Insight 4 Summer 2017 www.efp.org/perioinsight DEBATE EXPERT VIEW FOCUS RESEARCH Editor: Joanna Kamma What is the extent of the role played by genetic factors in periodontitis? Discover latest JCP research hile genetic factors are known to play a role in In a comprehensive overview of current knowledge, The Journal of Clinical Periodontology Wperiodontitis, a lot of research still needs to be they outline what is known today and discuss the (JCP) is the official scientific publication done to understand the mechanisms that are involved. most promising lines for future inquiry. of the European Federation of Indeed, the limited extent to which the genetic They note that the phenotypes of aggressive Periodontology (EFP). It publishes factors associated with periodontitis have been periodontitis (AgP) and chronic periodontitis (CP) may research relating to periodontal and peri- identified is “somewhat disappointing”, say Bruno not be as distinct as previously assumed because they implant diseases and their treatment. G. Loos and Deon P.M. Chin, from the Academic share genetic and other risk factors. The six JCP articles summarised in this Centre for Dentistry in Amsterdam. More on pages 2-5 edition of Perio Insight cover: (1) how periodontitis changes renal structures by oxidative stress and lipid peroxidation; (2) gingivitis and lifestyle influences on high-sensitivity C-reactive protein and interleukin 6 in adolescents; (3) the long-term efficacy of periodontal Researchers call regenerative therapies; (4) tooth loss in generalised aggressive periodontitis; (5) the association between diabetes for global action mellitus/hyperglycaemia and peri- implant diseases; (6) the efficacy of on periodontal collagen matrix seal and collagen sponge on ridge preservation in disease combination with bone allograft. Edited by Maurizio Tonetti, the JCP is call for global action to reduce the published monthly and has an impact A impact of periodontal diseases on factor of 3.477. health and well-being has been issued More on page 7-8 in a health-policy paper published in the Journal of Clinical Periodontology (JCP), CONTENTS the EFP’s scientific journal. The paper has been endorsed or Role of genetic factors in supported the EFP and 50 other periodontitis Page 2-5 international and national societies of periodontology. Experts call for global action Page 6 More on page 6 Latest JCP research Pages 7-8 Partners Issue 4 - Summer 2017 2 EXPERT VIEW What is the extent of the role played by genetic factors in the aetiology of periodontitis? By Bruno G. Loos and Deon P.M. Chin. While genetic factors are known to play a role in periodontitis, a lot of research still needs to be done to understand the precise mechanisms involved. Indeed, the limited extent to which the genetic factors associated with periodontitis have been identified is somewhat disappointing, although there are some promising lines of inquiry. eriodontitis is a complex chronic Fig. 1. Genetic multi-causality model for periodontitis Pinflammatory disease, in which there are multiple causal components1 that play their aetiological roles simultaneously and interact with each other. At least five domains of causal risk factors can be distinguished for periodontitis (see Fig. 1): 1. Environmental factors (a dysbiotic subgingival bacterial biofilm); 2. Genetic risk factors; 3. Lifestyle factors such as smoking, poor diet, and stress; 4. Systemic diseases, such as diabetes; 5. Other factors, as yet unknown but most likely also including tooth-related, occlusal, and iatrogenic factors. Within the domain of genetic risk factors for periodontitis, not only do certain genetic variations play a role, epigenetic changes in DNA are also involved. For the last 20 years, the periodontal community has followed the classification of two distinct phenotypes of periodontitis: aggressive Note: The multicausality model for periodontitis. Causal factors are ordered in five domains and periodontitis (AgP) and chronic periodontitis (CP). they play a role simultaneously, as well as interact with each other. Importantly, the relative AgP occurs most often at a younger age (up contribution of each causal factor varies among patients, therefore the size of each “piece” of to 35 years old) and these cases involve more the pie chart should be estimated per individual patient. genetic risk factors than CP cases (see Fig.2). See: Loos, B. G., Papantonopoulos, G., Jepsen, S. & Laine, M.L. (2015). What is the contribution of genetics to However, the phenotypes AgP and CP may not periodontal risk? Dental Clinics of North America, 59, 761-780. be as distinct as previously assumed and thus may not really be separate entities, because they do share genetic and other risk factors. It has been long recognised that cases of AgP can As in other complex chronic diseases, it is important The most common genetic variation between occur also in people aged over 35 and that cases to realise that a multitude of genetic variations individuals is called a single nucleotide of CP can occur in those below this age. (probably more than a hundred) are involved, so polymorphism (SNP). The frequency of a SNP is periodontal disease is called polygenic. on average one per 300 nucleotides. Nonetheless, almost all current studies on genetics use the defined disease entities: Taking this into account, it is somewhat Therefore, it is estimated that there are over 10 either AgP or CP. This has helped researchers to disappointing that, in the case of periodontitis, million SNPs in the human genome. These are focus on well-described case-control studies, the genetic factors associated with or annotated in the haplotype map (HapMap). something that is much needed in the search for contributing to the pathogenesis have been There are different types of SNPs: noncoding, identified only to a very limited extent and have genetic risk factors.2 coding, and regulatory polymorphisms. In been poorly validated. addition, there are other genetic variations such Genetic basis of periodontitis It is also possible that genetic variants as variable number tandem repeats (VNTR), On the basis of epidemiological studies of twins associated with periodontitis in, for example, nucleotide insertions and nucleotide deletions. and families with a higher rate of AgP, it can Caucasians may not be associated with other Variants in 38 genes have been associated with be concluded that in the younger patients the ethnic populations such as Asians, Brazilians, periodontitis, identified by using either the genetic contribution may account for as much and Africans. While a considerable overlap of candidate-gene approach or by genome-wide as 50% of causal factors, while in the older genetic variants between different ethnicities is association studies (GWAS) (see Table 1). patients a genetic contribution of at most 25% expected, it is important to realise that there will has been estimated.3 also be population-specific variants of risk genes. Issue 4 - Summer 2017 3 EXPERT VIEW Fig. 2. Genetic contribution to the aetiology of periodontitis to the discovery of novel candidate genes that have not been known or previously hypothesised – which yields not only new genetic risk factors but also the genetic variants found in GWAS can point to hitherto unknown genes and proteins. This enables the investigation of possible roles in biological pathways, especially in diseases such as periodontitis in which the pathophysiology is not well understood. The results of an initial GWAS need to be replicated (validated) in an independent case-control cohort with the candidate-gene approach. Until now five GWAS related to periodontitis have been performed. Genetic variants A total of 38 genes have been identified, in which one or several genetic variants have been associated with periodontitis, based on either the candidate-gene approach or GWAS (see Table 1). Only original genetic studies in which at least 100 cases and at least 100 controls were enrolled were considered in this brief review; however, Note: The genetic contribution to the aetiology of periodontitis in relatively younger individuals this low cut-off level may still yield false positive 3 with aggressive periodontitis has been considered higher than in older individuals with chronic results (type I error). periodontitis. In older individuals, environmental factors (a dysbiotic subgingival bacterial The table presents a global compilation, biofilm), lifestyle factors, systemic disease, age (immune senescence) contribute more to summarising the results from studies that have periodontitis development, whereas genetic factors play a smaller role. included different ethnicities. The genes which See: Loos, B. G., Papantonopoulos, G., Jepsen, S. & Laine, M.L. (2015). What is the contribution of have variant alleles (minor alleles) associated genetics to periodontal risk? Dental Clinics of North America, 59, 761-780. with both AgP and CP, with AgP only, with CP only, or just with periodontitis (PD) are listed in the table in sequence of the number of independent studies available. A given gene Candidate-gene approach be excluded.3Findings of negative associations with an SNP association with the disease in at for one selected SNP cannot rule out a potential Most often, the genetic loci, and the genetic least two independent studies provides greater disease association of the gene in question. polymorphisms that are positioned within these certainty about the validity. loci, have been chosen for candidate-gene studies Therefore,