09:19am Tuesday 02 June 2020

Two of a Kind – Why Study Twins?

For more than 30 years, Virginia Commonwealth University researchers have studied twins to understand the causes and contributing factors of health conditions to help shed some light on how much of our susceptibility for a disease or condition is influenced by our genes or the environment.

What’s ideal about studying twins is that they are a natural experiment. With identical twins, researchers have a pair of individuals who are born with identical genetic compositions and a predominantly shared environment. Their environments may begin to change as they begin to make divergent decisions as they get older that come with lifestyle, diet or friends. In contrast, nonidentical twins, also known as fraternal twins, are genetically no more alike than ordinary brothers and sisters, but experience a shared environment during their upbringing, similar to that of identical twins. These varying degrees of genetic and environmental similarities provide scientists with a variety of interactions to learn more about the causes of diseases and conditions.

In the mid-19th century, English scientist Francis Galton was among the first to put forward – in a scientific context – the idea of nature versus nurture, and he believed that any differences within pairs of identical twins had to be due to differences in the environment in which they were raised.

At VCU, researchers have been working with twin populations to gain insight into the genetics of psychiatric illness such as major depression, anxiety disorders, schizophrenia and alcoholism and drug abuse.

More recently, researchers here have begun to study to what extent the composition of the microbiome – the microorganisms we carry around with us – are affected by our genes.

“Studying twins provides a first-hand account whether genes are important for these things – because if genes are important then you would expect nonidentical twins to be less alike for something that you are measuring than identical twins,” said Lindon Eaves, Ph.D., distinguished professor of human genetics and co-director of VCU’s Virginia Institute for Psychiatric and Behavioral Genetics.

Eaves, a behavioral geneticist, is working with a team of cross-disciplinary researchers at VCU to examine how microorganisms found in the vagina influence health and disease in women. Eaves’ extensive research career spans some 40 years and looks at how genes and environment influence human behavior.

According to Eaves, this is not the first time VCU has been involved with a microbiome study. About 25 years ago, the VCU School of Dentistry took samples from twins to examine the composition of the microbiome of the mouth.

Useful Resource: MATR

For the vaginal microbiome project at VCU, the team is in the recruitment process and hopes to include approximately 250-350 twin pairs. These twins are not selected for any particular disease and will come from the VCU Mid-Atlantic Twin Registry, or MATR.

The registry contains a population-based record of twins from Virginia, North Carolina and South Carolina. MATR is an important research resource supported by the VCU Office of Research and can be used by researchers from both within VCU and beyond. Judy Silberg, Ph.D., one of the co-investigators for the vaginal microbiome study, is the scientific director of MATR and associate professor in the Department of Human Genetics in the VCU School of Medicine.

A second source for recruiting female patients is through the clinics at the VCU Medical Center. Female patients who visit the particular clinics here are asked if they are a twin. If they indicate they are, they are invited to enroll in the MATR and to participate in the study. Using this recruitment method, the team will be able to study both a twin who is likely to be diagnosed with a potential health issue, and her co-twin, said Eaves.

Eaves said that the early part of the study would allow for the team to get a sense of the natural variability between identical twins and also characterize similarities within repeated measures of the same person. 

“When you look at behavioral measures, quite a lot of what makes one twin different from the other – the environmental things are actually these very short-term effects. So if you look at personality, for example, most of the differences between identical twins are really short term and depends how the twin feels on the day she fills out the questionnaire or does the interview,” explained Eaves.

While the team is just getting started, Eaves said that the team’s preliminary data suggests that nonidentical twins are less alike in their microbiomes than identical twins and there are large individual differences in just the composition of the microbiome. They have also observed constellations of microorganisms that seem to go together and plan to further investigate how the number of these clusters may be influenced by the genes of the woman carrying them.

VCU is one of eight schools across the country studying the human microbiome and its relevance to disease as part of the National Institutes of Health Human Microbiome Project, a $157 million, five-year effort launched in 2008 as part of the NIH Common Fund’s Roadmap for Medical Research.

In addition to the vaginal microbiome being studied at VCU, other institutions will be studying and collecting data on the gastrointestinal tract, oral cavity, naso-pharyngeal tract and skin.

For more information about the VCU Mid-Atlantic Twin Registry, or to register as a twin, visit http://www.matr.vcu.edu/index.html or call 1-800-URA-TWIN.

Sathya Achia Abraham
VCU Communications and Public Relations
(804) 827-0890
[email protected]

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