**4. Genetic polymorphisms and periodontal disease**

A polymorphism is a form of genetic variant that appears in at least 1% of a population and evolves from mutation. 90% of polymorphisms come from Single Nucleotide Polymorphisms (SNPs) where a single base of one nucleotide is replaced with another. In majority of SNP that occur in genes, the protein produced remains unaffected, but have an effect on the gene product. Since all forms of periodontal disorders are linked with bacterial infections, outlining the relative roles of genes and environmental factors in these complex disorders is a challenge [47]. In case of chronic periodontitis, studies on twin adults imply that a sizable proportion of the population variance for periodontal measures such as pocket depth, attachment loss, and bone loss might be endorsed to genetics. Early onset periodontitis is often genetic, and the likelihood of inheriting periodontitis is high, as indicated by genetic studies [48].

A large part of in vitro and in vivo analyses [49] of human tissues as well as studies in animals strongly confirms that cytokines play a key role at all stages of the immune response in periodontal disorder. The various genetic polymorphisms associated with periodontal diseases are shown in (**Figure 1**).

#### **4.1 Inflammatory and anti-inflammatory cytokines**

#### *4.1.1 Interleukin-1*

IL-1 gene polymorphisms were the first described genetic markers related to periodontal disease in 1997 [10]. The three cytokines originally defined as the members of the IL-1 family were IL-1α and IL-1β, are the major agonistic molecules, whereas IL-1Ra, a biological antagonist. These functionally similar molecules are encoded on separate genes in the same region of chromosome 2. SNP's were found in IL-1 gene cluster, a C to T transition at nucleotide: 889 in the IL-1α and the second at +3954 of IL-1β gene. Occurrence of allele 2 of the IL-1B +3953 SNP was significantly increased in patients with advanced periodontal disorder [50–54].

*Dental Implants:* Investigations in individuals with polymorphisms of IL-1α and IL-1β genes with IL-1β – 511 2/2 genotype showed evidence of a substantially higher incidents of marginal bone loss [55].

*Intrabony defects*: Impact of IL-1 gene polymorphism on clinical and radiographic healing results in patients treated with Guided Tissue Regeneration (GTR) therapy [56] did not reveal any statistical variations between IL-1 + and IL-1 – patients.

#### *4.1.2 Interleukin-2*

It is established that – 330 (T → G) polymorphism in IL-2 gene is related to acute and vital role in pathogenesis of periodontitis [57].

#### *4.1.3 Interleukin-4*

Study of IL-4 gene polymorphisms in the intron 2 and in the promoter positions (PP+ and IP+) showed no link with periodontal disease exposure.

#### *4.1.4 Interleukin 6*

IL-6 in intron 2 and in the promoter positions (PP- and IP) gene polymorphisms in chronic periodontitis suggested that −572 G/C polymorphisms of IL-6 gene may be one of the protecting factors connected with lower susceptibility to chronic periodontal disease [50–53].

*Genetics and Periodontal Disease: An Explicit Insight DOI: http://dx.doi.org/10.5772/intechopen.99266*

**Figure 1.**

*Flowchart showing the various genetic polymorphisms associated with periodontal disease.*
