IL9 and schizophrenia: Periodontal disease and its progression may be negatively impacted by changes in inflammatory-related genes, genetic polymorphism of cytokines, and proinflammatory cytokine dysregulation in schizophrenia patients, which includes an elevation in levels of IL-1, IL-6, IL-9, TNF α, TNF β, PGE2, and CRP [21,22].