Depression, Genes, Cytokines, Chronic Fatigue, Physical Illnesses and Quality of Life

Depression is one of the most common psychiatric diseases, with prevalence estimates ranging from 5% to 20%. Depression is now recognized as a brain disease; it can be managed and treated effectively with a wide range of options, but its biological basis is still far from clear. Studies of monozygotic and dizygotic twin pairs suggest polygenic inheritance, with an overall heritability estimate between 40% and 70 %. Gene-environment interaction has been recognized for a long time in the pathophysiology of depression, and its best biological substratum at present is represented by the serotonin transporter (5-HTT) gene. It would be interesting to study association between the novel allelic variants or at least the triallelic 5-HTTLPR polymorphism and depression. Depression is common in patients with end-stage renal disease and to occur in about 20% to 30% of hemodialysis patients. Interferon-induced depression is estimated up to 50% among patients with hepatitis C. Several sets of observations support the supposition that cytokines, and proinflammatory cytokines in particular, are involved in depressive disorders. Depression sufferers have been reported to have elevated blood levels of interleukin 1 (IL-1), IL-6 and tumor necrosis factor α (TNF-α).