IFNG and periodontitis: The genetic polymorphism in some situations may cause a change in protein that leads to a change in innate and adaptive immunity.27Some single nucleotide polymorphisms were associated with severe chronic periodontitis.11Meta-analysis study about periodontitis and IFNg +874A/T showed the inconsistency of the results of +874A/T polymorphism and periodontitis risk that may be attributed to several factors such as race, type of periodontitis, study design, and environmental factors.