The power of two: epigenetics and twins

THG epigenetics blog post

This blog post was written by Jeff Craig

Special Epigenetics issue of Twin Research and Human Genetics

Twins are at the forefront of research into human health and disease. Twin Research and Human Genetics has published a Special Section highlighting how researchers have learned how epigenetics, the molecules that play the symphony of life on our genes, can influence our future health. Never before have such a group of papers been brought together in a single issue.

Papers highlight the power of sampling the same twins over time as their health changes and others detail the ways in which researchers scour the human genome for evidence of epigenetic associations with disease.

Four of the papers focus on the discordant identical twins in which only one twin has an illness. Topics span a wide age range of subjects, from birth weight to hormone replacement therapy (HRT). One even focuses on whether twins are “morning” or “evening” people.

Three papers from the Netherlands Twin Registry highlight the power of collecting biological samples from many hundreds, even thousands, of twin pairs. These are studies of aggressive behaviour, tic disorders and wellbeing and pinpoint specific epigenetic differences linked with each.

The final paper looks at the influences, both genetic and environmental, on how we age epigenetically.

In summary this special section is a clear snapshot of cutting edge twin research that is relevant for our hunt for the genes that influence all of our health.

You can read the articles included in this Special Section free of charge for a limited time here, or using the individual articles linked below.

See below for more details about the papers included in this special issue:

Read the full editorial from Jeff Craig and Richard Saffery, The Power of Two: Epigenetics and Twins

Chiarella et al: “This paper reviews the literature showing how monozygotic twin designs can be used to study epigenetic mechanisms that may explain the impact of early in utero and postnatal environmental factors on the development of psychopathology. “

Tsai et al: “this study of adult identical twins born with different weights found a biological legacy in a gene involved in fetal growth. This suggests that the environment we encounter in the womb can influence us for many year after.”

Bahl et al: “using twins discordant for hormone replacement therapy (HRT) the authors showed that HRT can change the activity of genes in the blood and that many of these genes were associated with sense of smell. This makes sense as HRT is known to improve a woman’s sense of smell.”

Wong et al: “believe it or not, some identical twins are more “day people” while their twin brither or sister are “night people. This study showed that our preference for day or night could be programmed in ‘epigenetic’ factors that stick to our genes and change their activity”

Du et al found an ingenious way to tell which of a pair of identical twins a sample found at a crime scene came from. Identical Twins cannot be distinguished because of their identical DNA but these researchers used “epigenetics”, factors that sit on top of the DNA”.

Bui et al: “identical teenage twins that had separate placentas in the womb may have a greater difference in the activity of their genes than those who shared a placenta. This shows that the environment we encounter in the womb can have long lasting effects”

Zilhao et al and van Dongen et al: “These twin studies of both tic disorders and aggressive behaviour identified changes to gene activity in the blood in genes related to brain function, suggesting that looking at the blood may reveal information about how such disorders are caused.”

Baselmans et al: “study showed that wellbeing in twins is associated with factors that control gene activity.“

Li et al: “study suggests that the variation in methylation acceleration due to unmeasured genetic factors is likely to be even lower that the 40% estimated in previous studies”

Explore the online archive of AGMG

AGMG cover-1
Cambridge University Press and Twin Research and Human Genetics (TRHG) are proud to announce the release of the online archive of AGMG, the predecessor journal to TRHG. AGMG was the official journal of the International Society for Twin Studies (ISTS) from 1952-1998 when TRHG took over this role. However, both journals have always had a wider interest in the field of human genetics.

Twins can provide unique and powerful opportunities to study genetic and environmental factors that make people differ in how they look, behave and how healthy they are. Monozygotic [identical] twins share all their genetic variation and dizygotic [non-identical] twin pairs, on average, share about 50% of their genetic variation. Both types of twin pairs often but not always share similar pre- and post-natal environments as well. Having twins participate in these studies helps to continue important research for common human conditions such as diseases, health, and behaviors, leading to advances in science, medicine and future potential therapies.

Much effort has gone into creating this digitised archive and making it available online to the research community because we believe that many of the classic papers published in AGMG reveal the academic foundations of the subject and still have relevance today. Below is a link to the 20 most cited papers from the AGMG archive to demonstrate the wide scope of interest. We encourage you to explore and enjoy this fascinating resource.

View the 20 most-cited papers from the AGMG archive here .

The papers cover a wide spectrum of topics and include the following articles:

  • Population-Based Twin Registries: Illustrative Applications in Genetic Epidemiology and Behavioral Genetics from the Finnish Twin Cohort Study (1990)
  • Resting Metabolic Rate in Monozygotic and Dizygotic Twins (1985)
  • Causes of Variation in Drinking Habits in a Large Twin Sample (1984)
  • The Vanishing Twin (1982)


Toddlers’ aggression found to be associated with genetic factors

Kids fighting

The development of physical aggression in toddlers is strongly associated with genetic factors and to a lesser degree with the environment, according to a new study led by Eric Lacourse of the University of Montreal and its affiliated CHU Sainte-Justine Hospital. Lacourse’s team worked with the parents of identical and non-identical twins to evaluate and compare their behaviour, environment and genetics.

“The gene-environment analyses revealed that early genetic factors were pervasive in accounting for developmental trends, explaining most of the stability and change in physical aggression, ” Lacourse said. “However, it should be emphasized that these genetic associations do not imply that the early trajectories of physical aggression are set and unchangeable. Genetic factors can always interact with other factors from the environment in the causal chain explaining any behaviour.”

Over the past 25 years, research on early development of physical aggression has been highly influenced by social learning theories that suggest the onset and development of physical aggression is mainly determined by accumulated exposure to aggressive role models in the social environment and the media. However, the results of studies on early childhood physical aggression, initiated by the University of Montreal team, indicate that physical aggression starts during infancy and peaks between the ages of 2 and 4. Although for most children the use of physical aggression peaks during early childhood, these studies also show that there are substantial differences in both frequency at onset and rate of change of physical aggression due to the interplay of genetic and environmental factors over time. Genetically informed studies of disruptive behavior and different forms of aggression across the lifespan generally conclude that genetic factors account for approximately 50% of the variance in the population.

Lacourse and his colleagues posited and tested three general patterns regarding the developmental roles of genetic and environmental factors in physical aggression. First, the most consensual and general point of view is that both sources of influence are ubiquitous and involved in the stability of physical aggression. Second, a “genetic set point” model suggests a single set of genetic factors could account for the level of physical aggression across time. A third pattern labeled ‘genetic maturation’ postulates new sources of genetic and environmental influences with age.

“According to the genetic maturation hypothesis, new environmental contributions to physical aggression could be of short duration in contrast to genetic factors,” Lacourse explained.

Read the full article here.

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