Systemic factors, such as diabetes mellitus (6) and smoking (7), can contribute as modifying factors to the progression of periodontitis by increasing the release of pro-inflammatory mediators, such as interleukins (IL-1α, IL-1β and IL-6), tumor necrosis factor-alpha (TNF-α) and prostaglandins (8, 9). The gene discussed is TNF; the disease is diabetes mellitus.