Although heightened risk of hepatitis among HBsAg+ patients receiving anti-TNF agents has been reported in individual cases and small clinic-based cohorts, the risk estimates provided by such studies are imprecise [1, 6–11]; for example, the risk may be influenced by sex, age, type of immune-mediated disease and, especially, concomitant hepatotoxic agents [12]. The gene discussed is TNF; the disease is hepatitis A virus infection.