*4.2.7 Vitamin D receptor (VDR) polymorphisms*

Vitamin D receptor gene polymorphism has influence on bone mineral density and turnover. Studies proved vitamin D receptor (VDR) gene is localised in chromosome 12 with a group of polymorphisms: BsmI, ApaI and TaqI and relationship between TaqI VDR gene polymorphisms and periodontitis.

### **4.3 Antigen–antibody gene polymorphism**

#### *4.3.1 HLA genetics*

The MHC genes are the most polymorphic genes present in the genome of every living organism. Research implied that patients with HLA-DRB1\*1501- DQB1\*0602 genotype may have accelerated T cell response and are thereby prone to periodontitis.

#### *4.3.2 Immunoglobulin g2 variations*

IgG molecules constitute genetically strong variants in the gamma heavy chains, termed Gm allotypes. Patients with rapidly progressing periodontitis with positive Gm shows higher antibodies [54].

#### **4.4 Polymorphism in genes encoding enzymes**

#### *4.4.1 Cathepsin C gene polymorphism*

Cathepsin C is a lysosomal protease in neutrophils and macrophages identified in chromosome 11, responsible for periodontal disease in young children termed as prepubertal periodontitis [51, 52].

#### *4.4.2 Matrix metalloproteinases(MMP) polymorphisms*

MMP-1 is an important mediator of connective tissue destruction in periodontal disease. A single nucleotide polymorphism in the promoter position of - 1607 bp of MMP-1 gene a, 5′-GGA-3′, instead of 5′-GAT-3′ has been identified to be linked with higher threat of generalised aggressive periodontitis [58].

#### *4.4.3 Polymorphisms in cyclogenase* −*2 gene*

PGE2 is a significant mediator of tissue destruction, catalysed by COX-2. A SNP of COX-2 in the chromosome 9q32–33. This modifies the expression of the COX-2 gene and polymorphism of -765G to C is linked with lesser risk for periodontitis.

*4.4.4 Polymorphisms in genes encoding myeloperoxidase (MPO) and N-acetyl transferase (NAT-2)*

A SNP in the promoter position of −1607 bp of MMP-1 gene a, 5′-GGA-3′, instead of 5′-GAT-3′ has been learned to be connected with increased risk of generalised aggressive periodontitis. A link between bone density loss in periodontal disease and polymorphism of NAT2 have been reported [59].

#### *4.4.5 Polymorphisms in genes encoding vasoactive enzymes*

The study of genotypes between affected and healthy showed the presence of lymphotoxin-á (TNF-â), angiotensin- converting enzyme and endothelin-1(ET-1) polymorphism with link to three-locus combination [41, 60].
