In a cross-sectional survey of California twins born between 1957 and 1982, self-reported lifetime asthma prevalence has been increasing significantly from older to younger twins, and corresponds to the high level self-reported in the U.S. as a whole, where millions of cases contribute significantly to the total healthcare burden. Earlier research has revealed inconclusive evidence of an association between family composition in early childhood and asthma risk. Any approach to prevention depends on knowing more about this link.
Based on a retrospective case-control study, the data provided by twin pairs was used in this thesis to examine by multivariate analyses differences in family size and birth order between pairs with no reported asthma and separate case groups of asthma-discordant and asthma-concordant pairs that represent asthma of sporadic and familial origin, respectively.
Results: (1) First and second born twins have a higher risk of asthma than twins third born or later. (2) Risk seems to be unaffected by sibship size alone. (3) Twins who were either last born with only one non-twin sibling or twins who were not last born had a higher risk of asthma compared to those who were last born with at least two older non-twin siblings. (4) The effects of birth order were generally greater among asthma-concordant compared to asthma-discordant twin pairs. (5) The effects of birth order were greater in pairs whose asthma was diagnosed prior to 8 years old (although limited power produced results that were borderline significance). Conclusions: Birth order appears to affect the risk of asthma, especially when acquired before 8 years old, and there is there is evidence that the effect is stronger among concordant pairs, suggesting a genetic environmental interaction.
|Commitee:||Gauderman, William J., Hamilton, Ann S., Mack, Thomas M., McConnell, Rob|
|School:||University of Southern California|
|Department:||Applied Biostatistics and Epidemiology|
|School Location:||United States -- California|
|Source:||MAI 48/05M, Masters Abstracts International|
|Subjects:||Public health, Epidemiology|
|Keywords:||Asthma, Birth order, Family size, Twin studies|
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