Levels of immunoglobulin G (IgG) antibodies and serum tumor necrosis factor levels have been found to discriminate between normal subjects and AD patients [7], and recently Sparks Stein et al. [13] found that elevated antibody levels to periodontal disease bacteria were observed in subjects years before cognitive impairment, suggesting that periodontal disease could potentially contribute to the risk of AD onset or progression. The gene discussed is TNF; the disease is Alzheimer disease.