RESUMO
SETTING: Studies showing significantly higher concordance of tuberculosis 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 hypersensitivity to tuberculin after newborn BCG immunization of twins suggested genetic regulation of the response to BCG in humans. DESIGN: Our study population consisted of 17 monozygotic twin pairs, 18 dizygotic twin pairs, and 64 single infants 3-34 months of age from Santiago, Chile. All had a BCG scar and were tuberculin tested by one trained nurse. RESULTS: The mean birth weight of both groups of twins was significantly lower than that of singletons and the percentage of individuals who failed to respond to tuberculin was approximately twice as high in twins as in singletons. After adjustment for birth weight and age by regression analysis, it was found that the distribution of tuberculin reactivity in both monozygotic and dizygotic twins was not significantly different from that of singletons. Both twin pair correlations is adjusted tuberculin reactivity were significantly greater than zero (P < 0.01) and led to a heritability estimate of 0.28. However, the monozygotic 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 response to newborn BCG immunization in humans by a mechanism capable of producing similar responses in identical and nonidentical twins alike.
Assuntos
Doenças em Gêmeos/genética , Hipersensibilidade Tardia/genética , Teste Tuberculínico , Tuberculose/imunologia , Gêmeos Dizigóticos , Gêmeos Monozigóticos , Vacina BCG , Pré-Escolar , Suscetibilidade a Doenças , Feminino , Humanos , Lactente , Recém-Nascido , Masculino , Tuberculose/prevenção & controleRESUMO
Scientific evidence has accumulated to show that chronic atrophic gastritis (CAG) is a precursor of gastric carcinoma, especially its intestinal histologic type; thus the etiology of CAG is of interest. Data on 110 families (557 individuals) collected as part of a large cohort from the Narino region of Colombia, South America, are analyzed to determine the familiality of CAG as a risk factor, and the possible involvement of a major gene in its etiology. We found that age and having an affected mother are important risk factors. In the sample, 45% are affected; 56% of individuals above 30 are affected, whereas only 28% of those 30 and under are affected; 48% of those with affected mothers are affected, but only 7% of those with unaffected mothers are affected. A positive spouse association was confounded with age. Sex and an affected father are not significant risk factors. The genetic (segregation) analysis showed Mendelian transmission of a recessive autosomal gene with penetrance dependent on age and mother's CAG status. Homozygous recessives account for an estimated 61% of the sampled population and have penetrance reaching 72% at age 30 if the mother is affected, and 41% if the mother is not affected. Carriers and non-carriers, who make up an estimated 39% of the sampled population, have an appreciable estimated risk after age 50. The environment, particularly diet, as the sole determinant of CAG needs reevaluation; some combined action of genes and environment seems more plausible.