A Twin Protection Effect? Explaining Twin Survival Advantages with a Two-Process Mortality Model

Simultaneous ST-elevation myocardial infarction in monozygotic twins: a case report of entangled twins

Background

The development of coronary artery disease (CAD) is strongly influenced by genetic and environmental factors. Monozygotic twins represent a unique population that provides insights into the interaction of genetic, environmental, and social factors and their effects on the development of CAD.

Case summary

Two 54-year-old identical twins presented to an outside hospital with acute chest pain. Twin B developed chest pain after witnessing Twin A in distress from an acute chest pain episode. Electrocardiogram performed on each of them was diagnostic of ST-elevation myocardial infarction. Upon arrival at the angioplasty centre, Twin A was taken for emergency coronary angiography yet his pain subsided on the way to the catheterization lab hence, Twin B was taken for angiography instead. Twin B angiography demonstrated acute occlusion of the proximal left anterior descending coronary artery and was treated with percutaneous coronary intervention. Twin A coronary angiogram demonstrated 60% ostial first diagonal branch stenosis with a normal distal flow. He was diagnosed with possible coronary vasospasm.

Conclusion

This is the first report of a simultaneous presentation of monozygotic twins with ST-elevation acute coronary syndrome. While genetic and environmental contributions to the development of CAD have been described, this case highlights the strong social bond that exists between monozygotic twins. Once CAD is diagnosed in one twin, aggressive risk factor modification and screening should be implemented in the other.

Lifespans of Twins: Does Zygosity Matter?

Studies with twins provide fundamental insights to lifespans of humans. We aim to clarify if monozygotic and dizygotic twin individuals differ in lifespan, that is, if zygosity matters. We investigate whether a possible difference in mortality after infancy between zygosities is stable in different age cohorts, and whether the difference remains when twins with unknown zygosity are taken into account. Further, we compare the distribution of long-livers, that is, the upper-tail of the lifespan distribution, between monozygotic and same-sex dizygotic twin individuals. The Danish Twin Registry provides a nationwide cohort of 109,303 twins born during 1870 to 1990 with valid vital status. Standard survival analysis is used to compare mortality in monozygotic and dizygotic twin individuals and twin individuals with unknown zygosity. The mortality of monozygotic and dizygotic twin individuals differs slightly after taking into consideration effects of birth- and age-cohorts, gender differences, and that twins are paired. However, no substantial nor systematic differences remain when taking twins with unknown zygosity into account. Further, the distribution of long-livers is very similar by zygosity, suggesting the same mortality process. The population-based and oldest twin cohort ever studied suggests that monozygotic and dizygotic twins have similar lifespans.

Human Dizygotic Twinning: Evolutionary-Based Explanations/Twin Research Reviews: Conjoined Twins in a Triplet Pregnancy; Double Embryo Transfer; Health Anxiety; Delayed Delivery of the Second Twin/In the Media: Digital Marketing Twins; Bereaved Twin at March for Our Lives; Exchange of Places; Football Players Reunite as Patriots

Human twinning poses a conundrum for researchers, given that the female uterus is optimally designed to carry a single fetus. Evolutionary explanations of dizygotic (DZ or fraternal) twinning provide insight and understanding of this reproductive event. This review is followed by summaries of recent twin research and reports concerning twins in a triplet pregnancy, double embryo transfer; a twin study of health anxiety, and delayed delivery of the second twin. Twin events reported in the media include a pair of digital marketing twins, a speech by a bereaved twin at the March for Our Lives in Washington, D.C., twins who exchanged places, and a same-team reunion of twin football players.

Correction: A Twin Protection Effect? Explaining Twin Survival Advantages with a Two-Process Mortality Model

[This corrects the article DOI: 10.1371/journal.pone.0154774.].

Insights into mortality patterns and causes of death through a process point of view model

Process point of view (POV) models of mortality, such as the Strehler-Mildvan and stochastic vitality models, represent death in terms of the loss of survival capacity through challenges and dissipation. Drawing on hallmarks of aging, we link these concepts to candidate biological mechanisms through a framework that defines death as challenges to vitality where distal factors defined the age-evolution of vitality and proximal factors define the probability distribution of challenges. To illustrate the process POV, we hypothesize that the immune system is a mortality nexus, characterized by two vitality streams: increasing vitality representing immune system development and immunosenescence representing vitality dissipation. Proximal challenges define three mortality partitions: juvenile and adult extrinsic mortalities and intrinsic adult mortality. Model parameters, generated from Swedish mortality data (1751-2010), exhibit biologically meaningful correspondences to economic, health and cause-of-death patterns. The model characterizes the twentieth century epidemiological transition mainly as a reduction in extrinsic mortality resulting from a shift from high magnitude disease challenges on individuals at all vitality levels to low magnitude stress challenges on low vitality individuals. Of secondary importance, intrinsic mortality was described by a gradual reduction in the rate of loss of vitality presumably resulting from reduction in the rate of immunosenescence. Extensions and limitations of a distal/proximal framework for characterizing more explicit causes of death, e.g. the young adult mortality hump or cancer in old age are discussed.