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Susceptibility to TB is often assumed to have a strong genetic component. The Prophit survey, published in 1963, involved 200 twin pairs in which at least one had developed active TB. The concordance rate for the second twin having active TB was approximately 32% in monozygotic twins and 14% in dizygotic twins. A reanalysis in 1978 showed inherited susceptibility to be a major determinant in the development of active TB. However, no genes have been consistently implicated in human TB susceptibility, and researchers have reanalyzed the survey data again.
In the present reanalysis, among the 87 twin pairs in which neither member was sputum smear–positive, the concordance rates for developing active disease were similar between monozygotic and …