Twin research : the official journal of the International Society for Twin Studies最新文献

Reports of fatigue preceding cardiac events have recently been confirmed by large prospective studies. To assess for genetic confounding, we investigated prolonged fatigue and cardiovascular disease (CVD) in a cohort of World War II veteran twins. We examined data from a questionnaire mailed to members of the National Academy of Sciences-National Research Council (NAS-NRC) World War II Twins Registry in 1998 and 1999 which included questions on demographics, medical conditions and symptoms of fatigue. Data from twins discordant for prolonged fatigue lasting a month or more were analyzed using conditional logistic regression. Among 1955 twin pairs, 157 monozygotic and 174 dizygotic pairs (mean age 74 years) were discordant for prolonged fatigue. An association was found between prolonged fatigue and a history of myocardial infarction or coronary artery surgery adjusting for age, socioeconomic status, smoking, alcohol use and depression (OR [Odds Ratio]: 2.2; 95% CI: 1.3-4.0). When analyses were performed separately by zygosity, the association was slightly larger for monozygotic (OR: 3.3; 95% CI: 1.2-9.1) than dizygotic twins (OR: 1.9; 95% CI: 0.9-4.0). These data corroborate the association of fatigue with CVD and suggest that it is not influenced by a common genetic factor. Further studies are needed to clarify the relationship and to better understand the biologic mechanisms.

Mothers of multiples who choose to feed their infants breast milk are faced with a seemingly overwhelming set of circumstances. Since mothers of multiples could potentially feed their infants differing proportions of breast milk, current methods of obtaining breastfeeding data for mothers of singletons may not adequately describe the breastfeeding behaviors of mothers of twins and triplets. The goal of our study was to determine the proportion of breast milk each infant of a multiple set was fed over a six-month period and compare the feeding regimens of sibling infants. Results of this retrospective study based on maternal reports indicated that there was almost complete agreement in the proportion of breast milk fed to siblings born from the same pregnancy, regardless of stratification based on gestational age, plurality, or location of the infants (hospital vs. home). The Pearson correlation coefficient for duration of breast-milk feeding between sibling twins was 0.99 (p < .0001); among sibling triplets the values were .97, .98 and .99 (p < .0001). A better understanding of the process by which twins and triplets are fed breast milk sets the stage for future research and can ultimately lead to the development of strategies to increase breast-milk feeding rates for multiple birth children.

It is shown that maximum likelihood estimation of variance components from twin data can be parameterized in the framework of linear mixed models. Standard statistical packages can be used to analyze univariate or multivariate data for simple models such as the ACE and CE models. Furthermore, specialized variance component estimation software that can handle pedigree data and user-defined covariance structures can be used to analyze multivariate data for simple and complex models, including those where dominance and/or QTL effects are fitted. The linear mixed model framework is particularly useful for analyzing multiple traits in extended (twin) families with a large number of random effects.