A common functional polymorphism (C → A substitution at position - 863) in the promoter region of the tumour necrosis factor-alpha (TNF-alpha) gene associated with reduced circulating levels of TNF-alpha. - Skoog,T.; van't Hooft,F.M.; Kallin,B.; Jovinge,S.; Boquist,S.; Nilsson,J. (Hum Mol Genet, 1999)