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Twins Studies & Epigenetics

Introduction:

I have friends who are non-identical twin brothers and I am pretty sure that most people who have socialised with twins will agree to how intriguing their behaviour and mannerisms often are.  Like many people I am fascinated by their physical similarity in appearance, but moreover by what intriguing similarities or differences may lie beneath the superficiality.  These very factors are at the core of scientific research involving twin’s studies and have led to important discoveries in terms of the role of genetics and heritability of disorder and disease. 

What about the Science?

Twin studies have provided the scientific community the opportunity to dissect and scrutinise the nature versus nurture debate. Research has involved the comparison of monozygotic or identical twins who share 100 % of their genes, to Dyzygotic or fraternal twins who share only 50% of their genes.  This type of comparative research has enabled the exploration of the roles that genes play compared to the environment and the balance of such factors involved in shaping individuals personality, behaviour and susceptibility. 

What have Twins Studies revealed to date?

Scientists have investigated rates of concordance for disease such as Schizophrenia and disorder such as Autism.  Research has revealed higher rates of incidence for those who share greater genetic similarity.  Evidence from this research supports the claim that genes and heritability are more influential to development of disease or disorder as opposed to the environment. 

Twins Studies & Epigenetic Research…the missing link!

Most recently, a new field of investigation has entered the realm of the nature versus nature debate.  Whereas past research involving twins has focused on their similarities, the new field of Epigenetics considers the likely cause of difference between twins.  The field of Epigenetics has extended previous research and it claims to offer a third factor that may be the key to unlocking the nature versus nurture debate. 

So what is Epigenetics?  Epigenetics investigates how factors such as stress and nutrition can affect gene performance.  Research suggests that Epigenetic tags or chemical mechanisms are attached to genes that can mutate in cases where individuals are exposed to environmental factors such as stress or poor nutrition.  

Epigenetics provides a feasible explanation then, for why in certain cases of monozygotic or identical twins, who despite sharing 100% of their genes, present with dramatic differences in the degree to which they are affected by disorders such as Autism.   

Epigenetics is an exciting new area of research that is receiving wider acknowledgement and acceptance as an additional intrinsic factor in the shaping individual’s behaviour.  Consequently it is receiving greater access to funding from within the global scientific community. 

The twin brothers with whom I am friends both have sons who have been diagnosed with Autism and I too have a son diagnosed with Autism, we have also had subsequent children who do not have the disorder.  A common thread that seems to run through our stories is that all of our children with the disorder suffered trauma either in-utero or during the first year of their lives.  Our stories and I’m sure many others provide evidence that corroborates the claims of Epigenetic research.  

http://www.youtube.com/watch?v=uW3x9rpXz5c

http://www.youtube.com/watch?v=nyck4rdP_Bc&feature=related

The Take Home Message!

This field of research is further demonstrating that nature and nurture are complex inter-twined causal explanations for the shaping of individuals behaviour rather than separate alternative explanations.  By understanding how gene mutations occur as a consequence of environmental factors, we may in future be able to prevent disease and disorder or at least have greater understanding and awareness of the causal factors.

Other Twins Studies & More Scientific Advances:

Once a year a festival takes place in the town of Twinsburg Ohio, aptly named so by its founders who were twin brothers.  During the festival period the town is besieged by many hundreds of twins.  Each year the festival has exhibitors of relevance to all matters pertaining to twins. 

Most recently exhibitors have included Patrick Flynn and colleagues, Computer Scientists from University of Notre Dame who have pioneered the latest in face-recognition software.  Flynn and his team took twin volunteers to participate in being photographed, finger printed and providing retinal scans.  Flynn’s objective is to establish whether this innovation in technology has the precision to distinguish between identical twins. 

Other exhibitors include the Monell Chemical Senses Centre of Philadelphia who can test and compare twins taste responses to alcohol.  Medical Doctors from Cleveland University hospitals whom are investigating women’s heath issues and Dermatologists from Proctor and Gamble whom are investigating the effects of skin damage.

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Categories: Uncategorized
  1. February 7, 2012 at 10:17 am

    It is clear that twin studies remain a vibrant component of psychology in that they have not only been used to examine the genetic etiology of illnesses, but also as you have stated, the interplay in genetic liability and environmental risk factors (Thapar & Rice, 2006). In addition to the investigation of schizophrenia they have facilitated in the investigation of depression and anorexia. McGuffin et al. (1996) found that if one monozygotic twin had major depressive disorder then in 46% of cases the other twin was also diagnosed with it. Whereas in dizygotic twins the concordance for major depressive disorder was only 20%. Gorwood, Bouvard, Mouren-Siméoni, Kipman and Adès (1998) investigated the incidence of anorexia in 34 twin pairs. Again they found a higher concordance rate in monozygotic twins (55%) in comparison to dizygotic twins. Nonetheless as 100% concordance among monozygotic twins has not been uncovered in these investigations there must also be an environmental link. Isolating the effects of genes and the environment is perhaps one of the fundamental issues with regard to twin studies. In relation to epigenetics Haque, Gottesman and Wong (2009) found monozygotic twins to have significant differences in obvious phenotypes like disease and epigenetic DNA modification patterns, strengthening your argument that despite monozygotic twins sharing 100% genes they may have varying degrees of a particular disorder.

    References
    Gorwood, P., Bouvard, M., Mouren-Siméoni, M., Kipman, A., & Adès, J. (1998). Genetics and anorexia nervosa: a review of candidate genes: Psychiatric Genetics, 8, 1-2.

    Haque, F., Gottesman, I., & Wong, A. (2009). Not really identical: Epigenetic differences in monozygotic twins and implications for twin studies in psychiatry. American Journal of Medical Genetics, 151, 136-144.

    McGuffin, P., Rijsdijk, F., Andrew, M., Sham, P., Katz, R., & Cardno, A. (2003). The heritability of bipolar disorder and the genetic relationship to unipolar disorder. Archives of general psychiatry, 60, 497-502.
    Thapar, A., & Rice, F. (2006). Twin studies in paediatric depression. Child and Adolescent Psychiatry, 15, 869-88.

    • September 11, 2012 at 7:36 pm

      i got your message really sorry but I cannot supply references as they were not supplied at source.:(

  2. February 10, 2012 at 6:19 pm

    Twins studies are excellent sources of information in terms of trying to establish a genetic link with a psychological disorder, for example schizophrenia, (MZ’s 40.4% concordance, DZ’s 7.4% concordance; Joseph, 2004). However this is not always possible as many twins share the same or very similar environmental setting from birth, which could have an equal influence over their behaviours/development of a disorder. For example being brought up by the same parents in the same house with the same toys etc etc, this is even more significant for identical twins who are often dressed and treated in exactly the same way especially in their young childhood. Another limiting factor is that twins share the same pre-natal environment, which means that if they both develop a hereditary disorder, this may stem from the relationship between mother and child in the womb and not necessarily their genetics, (although this would still show a biological link).
    In terms of epigenetics, suggesting that a parent’s experiences can be passed on to their offspring through ‘tags’ would explain some of the strange patterns in inheritance, however there is little quantitative evidence to support this theory in animals.
    Great blog, my only criticism is they’re supposed to be around 500 words max and this post is over 750 so try cutting down a bit next time 🙂

    References

    Joseph, J. (2004). The Fruitless Search for Schizophrenia Genes. Ethical Human Psychology and Psychiatry, 6,167-181.

    http://learn.genetics.utah.edu/content/epigenetics/inheritance/

  3. February 10, 2012 at 11:28 pm

    Although twins studies are very useful as you can compare concordance rate they are not always able to establish causality. This is a problem because you immediately get dragged into a nature vs. nurture debate, of which there are endless arguments and counter-arguments and inconsistencies. The most complex questions about humans are yet to be answered and although twin studies can allow important and interesting insight they are not enough on their own to make direct inferences.

  4. February 10, 2012 at 11:43 pm

    Twins, in all relevant matters, are mystifying. As they become the pioneers of matters arising in the study of psychology, concerning primarily the relationship between mental health and monozygotic or dizygotic twins, one’s interest simply cannot resist thickening. Epigenetics, in encountering the aforementioned factors of personality, behaviour and susceptibility, it is of my inclination to elaborate upon the third in order to consider it’s use: Susceptibility concerns many facades (influences, to peer pressure, the environment, behaviours, etc). Yet, susceptibility to what is societally ostracised, obesity, may be the fuel to a cycle that one issue that epigenetics drives; Franks and Ling (2010) found genes and the environment interact, forming the basis of the disorder of obestity. Genetically diverse subpopulations, the American Indians for example, were discovered to be more susceptible to becoming obese despite living in the same or comparable environment as those with less chances of developing obesity and it’s affiliated health issues. Hence, araising the issue that if even within subpopulations, when a higher chance of genetic predisposition exists, it is facilitated by monozygotic/dizygotic twins and therefore the two aspects (environment and twins) feed onto one another in a cycle. The cycle thereby produces a weakness in epigenetic studies, as the root is difficult to trace. For independent learning, it is preferred if the entry additionally supplemented the research and, at the least, skimmed evidence underneath the headline of ‘What about the science’.

    An additional note: In regards to the nurture façade of the nature vs nurture debate: what one must acknowledge, in regards to environment is their contributions, yet ‘deny their agency’ (Gesell, 1992).

    Anastasia

    References

    Franks, P., & Ling, C. (2010) BMC Medicine 8:88

    Gesell, A., L. (1992) The paradox of nature and nurture.

    • February 10, 2012 at 11:44 pm

      (Discount the remark near the bottom regarding moderation)

  5. Rachel
    September 7, 2012 at 3:14 pm

    IHMSL- can you please provide us with the references you used to compile the above graph in your blog post? Thanks.

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