TUBERCULIN REACTIVITY AFTER NEWBORN BCG IMMUNIZATION IN MONOZYGOTIC AND DIZYGOTIC TWINS

Setting: Studies showing significantly higher concordance of tuberculo sis among monozygotic twins than dizygotic twins have provided support for genetically determined susceptibility to tuberculosis. Objective: We wished to explore whether the development of delayed type hypersen sitivity to tuberculin after newborn BCG immunization of twins suggest ed genetic regulation of the response to BCG in humans. Design: Our st udy population consisted of 17 monozygotic twin pairs, 18 dizygotic tw in pairs, and 64 single infants 3-34 months of age from Santiago, Chil e. All had a BCG scar and were tuberculin tested by one trained nurse. Results: The mean birth weight of both groups of twins was significan tly lower than that of singletons and the percentage of individuals wh o failed to respond to tuberculin was approximately twice as high in t wins as in singletons. After adjustment for birth weight and age by re gression analysis, it was found that the distribution of tuberculin re activity in both monozygotic and dizygotic twins was not significantly different from that of singletons. Both twin pair correlations in adj usted tuberculin reactivity were significantly greater than zero (P < 0.01) and led to a heritability estimate of 0.28. However, the monozyg otic twin correlation was not significantly larger than the dizygotic twin correlation so that heritability is poorly estimated. Conclusion: These results are consistent with a genetic regulation of the respons e to newborn BCG immunization in humans by a mechanism capable of prod ucing similar responses in identical and nonidentical twins alike.