Genetics and Periodontal Disease: An Explicit Insight

*Santo Grace Umesh, Lakshmi Ramachandran, Janani Karthikeyan and Anitha Mani*

#### **Abstract**

A branch of Biology which deals with the science of hereditary influences on living organisms is termed as Genetics. There has been a broad study related to hereditary influence on human tissue linking to health and disease conditions. A vital role is played by genetics in the proper functioning, adaptive repair, regeneration and remodelling of hard and soft tissue. A major segment of genes are related to periodontal disease. Periodontal disease, being multifactorial in origin is directly or indirectly known to be caused by genetic factors also. A study on human and animals validates the concept that genetics could have influenced periodontal disorders and also plays a key role in the predisposition and progressiveness of the condition. The role played by genetics to damage the inflammatory and immune response system of the host tissues during periodontal conditions has been proved and this section will give a clear insight on the influence of genetics in this condition.

**Keywords:** Genetics, Periodontal disease, Hereditary influence, Polymorphism, Syndromes, Genetic study design

#### **1. Introduction**

A distinct approach is required for periodontal pathologies that produces lesions within the tooth- supporting tissues, once associated with risk factors which are complementary to systemic diseases [1]. Bacterial plaque is the prime aetiology of periodontal diseases, accelerating tissue damage. However, the role of plaque is debated when the vulnerability to periodontal diseases persist despite regular conditions. According to the majority of researchers' perspective, periodontal disease cannot occur in the absence of plaque and tartar, and also suggests that a systematic predisposition merely progresses the tissue destruction caused by microbial flora. On the other hand, few authors claim that there is no concrete evidence establishing cause-effect relationship between the nonspecific bacterial plaque and severity of tooth supporting tissue injury [2].

The host immune response system, the integrity of the tissues, humoral and cellular immunity, and certain endocrine and nutritional factors are the major factors for the development and progression of periodontal disease. Multitude of other factors are also related to periodontal diseases including age, intraoral sites that are more prone to infection and specific microbial agents such as Captosinofaga, Actinomyces naeslundi and Actinobacillus actinomycetemcomitans [2]. Apart from the host immune response system, these factors also add on to the vulnerability to periodontal disease, presenting simple to complex signs. Furthermore, the presence of associated metabolic disorders would also lead to periodontal damage [2].

Genetic elements play a vital role in influencing the inflammatory and immune response of the periodontal disease. Due to the key role played by the immune system in the pathophysiology of the disease, research is directed to identify the genetic mutation or polymorphism related to the various aspect of immunity. The result of these genetic variations might be minor or unimportant or very important and severe based on its effect and infectivity [3]. Genetic diseases are broadly classified into two entities: Simple Mendelian Disorders and Complex Genetics Disorders. Simple Mendelian Disorders are otherwise known as monogenic or single-gene disorders since they are caused by alterations of a single gene, acquired through autosomal recessive or dominant type of inheritance. Several monogenic gene disorders with biochemical defects present with severe periodontitis as one of their clinical manifestations. In these conditions, genetic alteration occurs at a single locus, producing the clinical phenotype which is responsible to cause the disease. Such a genetic alteration, that is associated with a disease phenotype in all families and there is no alternative mechanism to overcome the impact of the genetic defect, is termed as mutation [4].

Complex genetic diseases prevail in more than 1% of the population and are known to be more dominant than Simple Mendelian disorders. Being affected by environmental and lifestyle factors, complex genetic diseases occur as a result of genetic variations at multiple areas of the genes. Alterations in multiple genes, with each contributing a little to these complex genetic diseases, are called polymorphisms. Specific allele occurring in at least 1% of the population is known as genetic polymorphism. Single base mutation that replaces one nucleotide for another is said to be the simplest type of polymorphism and is termed as a single nucleotide polymorphism (SNP). Restriction fragment length polymorphism (RFLP) and simple tandem repeats (STRs), comprising of nucleotide or allele repetition are other types of polymorphism [5]. These genetic polymorphisms are not directly associated with the disease as in monogenetic disorders, however, specific alleles are found with greater incidence in the affected individuals than healthy individuals. The results prove to be true only when two different genetic variations coexist. Complex periodontal disorders are chronic, slowly progressive and are mostly of mild phenotype [5].

Variations in numerous genes encoding different proteins result in a genetic predisposition to a clinical phenotype. Environment and lifestyle play a significant role in impacting the development of complex diseases. Host response influenced by the genetic makeup is responsible for the progression of periodontal disease. Genetic defects or alterations can raise the incidence of periodontal disease. If the physiological process elicited by the gene is related to the occurrence and severity of disease, that specific gene is considered as a contributory element in periodontal disease [6]. Literature evidence reports that the genetic variants play a major role in the aetiology of syndromic and non-syndromic periodontitis.

#### **1.1 Terminologies**

#### *1.1.1 Allele*

One of two or more alternate forms of a gene or marker at a particular locus on a chromosome. (A glossary of relevant genetic terms –Dialogues in clinical neuroscience) [7].
