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The singular world of twins and twin studies

International Twin Congress and More

Highlights from the 2012 Twin Congress and new research on fraternal twins.

 

The 14th Congress of the International Society for Twin Studies

The 2012 Congress of the International Society for Twin Studies was held in Florence, Italy, April 1-4, 2012. The official opening of the meeting was a viewing of a photography exhibit, “Twins, Art and Science,” by Dr. David Teplica. It was held at the Instituto degli Innocenti, in the Piazza Santissima Annunziata. Photographs of identical twins revealed a number of remarkable physical asymmetries and resemblances. The Instituto degli Innocenti was designed by Filippo Brunelleschi, and served as an orphanage in the 15th and 16th centuries.

This congress is one of my favorite professional events because it is an opportunity to hear the latest, cutting-edge research on many biological and psychological features of twinship. Several pre-meeting sessions included discussion of how assisted reproductive technologies are affecting identical and fraternal twinning rates; the monitoring of multiple birth pregnancies; and epigenetic twin analyses (studies concerned with how differential gene expression may underlie differences between identical twins). Later that evening the membership attended an opening ceremony held at the Salone dei Cinquecento, Palazzo Vecchio, followed by a reception.

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Panels and presentations lasted three days, covering topics such as twinning rates, epidemiology, obstetrical issues and complex diseases. In addition, representatives of national organizations of parents of twins meet regularly at the ISTS. This group, called ICOMBO (International Council of Multiple Birth Organizations), is largely concerned with gathering and disseminating information regarding the rearing and educating of twins.

The ISTS scheduled the viewing of a documentary film, The Lone Twin, directed by Belgian filmmaker, Anna van der Wee. The film captures Anna’s tragic loss of her twin brother, Dirk, when the two were 20. Twin loss leaves survivors grappling with many different kinds of questions regarding the sense of oneself as a twin. The Lone Twin also probes the meaning of twinship through the reflections of a series of different twin pairs who are mostly fraternal. This is important and to the credit of the director—most media on twins focuses on identical pairs, owing to their visual interest. However, fraternal twins occur far more frequently among western populations, and comprise a vital comparison group in any twin study. It should also be noted that The Lone Twin includes the only filmed footage of a Yoruba ceremony involving the loss of a twin. The Yoruba, located in western Nigeria, have an unusually high twinning rate. Until this past year, that region was acknowledged as having the highest twinning rate in the world, but more recent study places Benin in first place.

The journal of the ISTS, Twin Research and Human Genetics, publishes six yearly issues devoted exclusively to twin studies. It has recently been taken over by Cambridge University Press. More about the twin congress can be found in a forthcoming issue,

 

Diagnosing Twin Type: Rare Fraternal Twin Pairs

Chorions and amnions are the outer and inner membranes, respectively, that surround the developing embryo. About one-third of identical twins have separate chorions, amnions and placentas, while most of the other two-thirds have a shared chorion and placenta, but separate amnions. A very rare group of identical twins shares the chorion, amnion and placenta. In contrast, fraternal twins typically have separate chorions, amnions and placentas. Now, however, it is recognized that a very small number of fraternal twins share a chorion. The most recent case occurred in Australia to a couple who spontaneously conceived twin boys, diagnosed as identical on the basis of their shared chorion. However, the twins looked different physically, causing their parents to question the diagnosis. Further medical study confirmed that the twins were fraternal, although the processes by which they developed a shared chorion continue to be debated. Families with twins whose observations strongly conflict with the twin type provided to them are advised to request additional information and testing.

 

Sources for Further Reading:

 

Smits, J., and Monden, C., (2011). Twinning across the developing world. http://www.plosoneorg/article/info%3Ado%2F10.1371%2Fjournal.pone.....

Umstad, M.P., Short, R. V., Wilson, M., & Craig, J. (2012). Chimaeric twins: Why monochorionicity does not guarantee monozygosity. Australian and New Zealand Journal of Obstetrics and Gynaecology, DOI: 10.1111/j.1479-828X.2012.01445.x.

 

 

 

 

 

 

 

 

 

Nancy L. Segal, Ph.D., is a Professor of Psychology and Director of the Twin Studies Center, at California State University, Fullerton.

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