**1. Introduction**

The interplay among the immune system, microbiota, and lifestyle habits like smoking, alcoholism, stress, and diet that leads to constant changes in the host is regulated by genes. These genes encode immune receptors and various molecules involved in the signal transduction pathways that play an essential role in up regulation or down regulation of the immune response essentially the inflammatory reaction in response to a stimuli. Genetic research has focused on understanding how these responses work and also how these responses differ between different individuals. In addition to playing a role in health, the genetic factors also plays a major role in disease susceptibility. This review focuses on the genetic aspects of periodontal diseases wherein researchers are currently focusing on genetic evidences to explain the difference in susceptibility to periodontal disease in different individuals.

Although very prevalent, periodontal diseases are not evenly distributed across populations. Few people, who do not have much contributing local factors such as plaque and calculus, still develop severe destruction of bone whereas some do not develop severe forms of periodontal diseases in spite of having a very poor oral hygiene. This differential expression of periodontitis leads researchers to question if genetics and heritability played a major role. The first evidence that genetics played a role in periodontal diseases emerged in the 1990s. Schafer et al. postulated that a key determinant of whether individuals developed periodontitis or not was

#### *Periodontal Disease - Diagnostic and Adjunctive Non-surgical Considerations*

dependent on the way their bodies responded to the microbes [1]. Genetic factors and environmental factors determine the susceptibility to disease.

A biomarker is a substance that could indicate a biologic state and is an objective measure to evaluate the current and future disease activity. The National Institutes of Health Biomarkers Definitions Working Group in 1998 defined a biomarker as "a substance that is measured objectively and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention." These biomarkers could be determined in various biological media like saliva, serum, and gingival crevicular fluid in health as well as disease. Generally, a combination of biomarkers is used in order to predict disease activity.

Genetic susceptibility to multifactorial diseases like periodontitis is usually due to several gene polymorphisms instead of a single, or few, gene mutations. Subtle variations in the genetic code may result in altered expression of the encoded proteins, thereby making individuals with genotypes more susceptible to a given disease.

The genetic link with the etiopathogenesis of periodontitis was started with the initial finding of association of composite genotype (Interleukin-1α and IL-1β) with chronic periodontitis in Caucasian population by Kornman et al. [2]. Following him, lot of studies conducted in different ethnic races linking the association of composite genotype with periodontitis. But the results were contradictory in nature. A variety of single nucleotide polymorphisms of various signaling factors, receptors, connective tissue components, enzymes involved in the host defense against the invading microbes have been reported by several researchers. Use of the genetic risk score could be useful in assessing the susceptibility to periodontitis. However, conflicting results have been reported because of the heterogeneticity of the studies. Different variations in frequency of some alleles in different populations have been observed.
