Why study genetic susceptibility to infection?

Historical accounts of the plague tell of individuals who survived unscathed in households where almost everyone else died. Each winter, British hospital wards are full of infants requiring oxygen therapy for bronchiolitis, but most infants infected with the same virus have little more than a runny nose. Over a million African children die each year of malaria, but many more remain in relatively good health despite being continually infected with the parasite.

To what extent does our genetic make up determine the different ways that we respond to the same infectious agent? This is difficult to answer because of the many other contributory factors involved, such as previous health, acquired immunity, and variability in the pathogen. Epidemiological analysis of the genetic component is confounded by environmental factors that cause familial clustering and is further complicated by the many different genes that are likely to be involved. Nevertheless, there is compelling evidence for a genetic component, including twin studies of tuberculosis,1 leprosy,2 malaria,3 and Helicobacter pylori infection4 and a large survey that found …