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Familial Aggregation of Chronic Obstructive Pulmonary Disease
Published in Stephen D. Litwin, Genetic Determinants of Pulmonary Disease, 2020
Bernice H. Cohen, Gary A. Chase
One variation of the twin-study approach has been very infrequently applied. That is the study of monozygotic twins who are discordant with regard to the disease under consideration for the purpose of identifying extrinsic factors that may have led to the difference in disease manifestation in two presumptively genetically identical individuals. This has been used by Cederlöf and co-workers [93,100] with some very interesting results (see Table 1 and section II above), although, as noted, caution is required in view of the potential pitfalls [104], This method, however, clearly deserves the consideration of researchers, particularly in conditions such as COPD where the importance of extrinsic agents as well as genetic factors is well recognized.
Twin Studies of Human Obesity
Published in Claude Bouchard, The Genetics of Obesity, 2020
Joanne M. Meyer, Albert J. Stunkard
The basic principle underlying the twin study is straightforward. MZ twins share all of their genes and part of their rearing environment, while fraternal (dizygotic [DZ]) twins share all of their rearing environment, but, on average, only one half of their genes. Consequently, the difference in similarity between the members of MZ pairs vs. those of DZ pairs reflects the extent to which a trait is genetically determined. If there is no difference in similarity between MZ and DZ pairs, it suggests that the trait arises solely from environmental effects. On the other hand, any MZ/DZ difference strongly suggests that the trait is heritable within the population under study.
The Microbiome in Multiple Sclerosis
Published in David Perlmutter, The Microbiome and the Brain, 2019
Helen Tremlett, Emmanuelle Waubant
The vast majority of studies in multiple sclerosis have been of a case–control design (Table 9.1). This is a very cost-effective way to study a given disease, especially if it is relatively “rare.” However, case-control studies are also very prone to selection bias; if the controls are not sourced from the same “at-risk” population as the cases, then differences between cases and controls might have very little to do with the actual disease being studied.53 Unfortunately, from where cases and controls are sourced and how they were selected could either not be determined in some studies, or were quite different (e.g., cases from a hospital setting vs. controls being University staff members, and/or from different cities, Table 9.1). The monozygotic twin study largely by-passes many of these shortcomings, as presumably most twins were raised together in a similar environment.29 Nonetheless, all of the studies are modest in terms of the number of multiple sclerosis cases and controls enrolled.
Resting heart rate and relation to disease and longevity: past, present and future
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 2019
Several genome-wide association scans of genetic loci associated with RHR have been performed, and so far, 64 loci have been found [32,33]. However, only a few percent of the variation in RHR has been explained by genetic factors. Another method for assessing genetic heritability is through twin studies [34,35]. Using the classic twin study methodology, a higher correlation in RHR between MZ twin pairs as compared with DZ twin pairs reflects genetic influences. Using information from the Danish Twin Study [24] almost 4300 twins were included to investigate the heritability of RHR. Here, there was a significant heritability of RHR, which was estimated to explain 23% (95% CI 15–30%) of the variation in RHR. A significant proportion of the variance in RHR is therefore attributable to heritable factors.
Pathophysiology of eosinophilic esophagitis: recent advances and their clinical implications
Published in Expert Review of Clinical Immunology, 2019
Melanie A Ruffner, Katie Kennedy, Antonella Cianferoni
Small and large studies have shown that genetic determinants are far greater than other atopic diseases such as asthma [27]. In a study of 4423 EoE cases and 24,322 controls from the Utah population database, it was demonstrated that risks of EoE were significantly increased among first-degree relatives (odds ratio [OR], 7.19; 95% confidence intervel [CI], 5.65–9.14) [40], especially those diagnosed by 18 years of age (OR, 16.3; 95% CI, 9.4–28.3) [40]. Similar results have been shown in twin studies, in which monozygotic twins have 41% disease concordance while the non-twin siblings of patients with EoE have a 2.4% disease concordance and the non-related population of 0.05% [28]. Therefore, the sibling risk ratio in EoE is estimated to be over 40 and only 2 for example for atopy [41]. However, the aforementioned studies shows also a great influence of the environment. Interestingly the Utah study found an increased risk of EoE in the spouses of EoE probands, which suggests either nonrandom mating or potential shared environmental contribution to development of EoE [40]. Similarly in the twin study, the dizygotic twins had a disease concordance of 22% much higher than the siblings’ concordance, indicating that both genetics and early life factors play important roles in the development of EoE [28].
An in-depth look into the association between morningness–eveningness and well-being: evidence for mediating and moderating effects of personality
Published in Chronobiology International, 2019
Magdalena Drezno, Maciej Stolarski, Gerald Matthews
There may be several mechanisms contributing to the affective correlates of morningness–eveningness. Behavior genetic studies suggest a biological basis for the trait; a recent twin study found that it shares a significant amount of underlying genetic variance with depression (Toomey et al. 2015). There may be a reciprocal relationship between neural circadian pacemakers and depression (Hidalgo et al. 2009). That is, the pacemaker may influence depression, but depressive symptoms such as sleep disturbance may feed back to further impair pacemaker functioning. Therefore, vulnerability to emotional disorder may in part be intrinsic to eveningness. Second, as we mentioned above, “owls” struggle with “social jet lag” and may experience greater social stress in consequence. Social jet lag refers to the discrepancy between circadian and social clocks resulting from variation in the sleep-wake cycle across weekdays and weekends (Wittman et al. 2006). It is linked to various symptoms of poor mental and physical health (e.g., Takahashi et al. 2018). E-types, who may be prone to a forward phase-shift in sleep at the weekends, are more likely to experience social jet lag (Díaz-Morales and Escribano 2015).