Overview

PETS is a research project being conducted by the Murdoch Children's Research Institute at The Royal Children's Hospital, Melbourne.

PETS is a study of twins, from when they were in the womb through to childhood and beyond. We aim to work out what makes us all who we are; our health, development, and wellbeing. We have started our research with twins, who share the same mother, but are usually in their own 'sac' during pregnancy, then share the same home environment as children. Despite this, even 'identical' twins can have different personalities, physical characteristics and illnesses. We want to know why these differences exist and what they can tell us about the first years of life.

It would be of great value to us if you have any suggestions or comments you would like to make about our research and what research questions interests you. Your comments could even inspire us to research something we hadn’t previously thought of.

There were 250 mothers of twin pairs who were recruited before their twins were born. Of these, 221 families agreed to take part again as their twin children reached six years of age. This is a remarkable 88% and a credit to all our families for the time and effort that is put into this research. Besides this, we also had some families who could not take part in this phase of the study because of work and family commitments, but who would like to continue in the study. We look forward to being able to discover more about the health and development of twins in these families in the future.

We are thrilled to report that over 90% of our participating families completed all three questionnaires about their twins’ health and development, dietary habits and preferences, their oral health and their families. Again, the time and effort that goes into responding to these questionnaires is very much appreciated. The information you can provide helps us to know more about twins, their families and to better understand any findings in the biological samples you provide. It also assists us in tracking the children from birth. 

More resources

• Twins Research Australia
• Essays on health: microbes aren’t the enemy, they’re a big part of who we are
• Fat or thin: can the bacteria in our gut affect our eating habits and weight?
• Breastfeeding and Growth of Children in the Peri/postnatal Epigenetic Twins Study (PETS): Theoretical Epigenetic Mechanisms

Information for participants

Access to birth records 

We are currently contacting all our families to ask whether we can access the hospital records about the birth of the twins. Some of you will have already received this request.

We hope to collect information from these records from as many families as possible. This is because, since you were recruited to the project, our understanding of how early life can predict future health and disease has improved.

It is now clear that we could gain a much better insight if we could clarify some of the information collected from you during your pregnancy and the delivery of your twins.

To ensure the information collected is accurate, we would like to access the pregnancy and birth medical records for you and your twins. Sometimes, we will seek to confirm information already collected from you through questionnaires. In others, we will seek information about new factors that we did not ask previously that are related to those we have already collected. An example of how this information could be used is to learn more about:   

• developmental anomalies of the teeth
• the relationship between genes, the environment in the womb, and tooth decay
• whether there are early predictors of autism
• the relationship between growth in the womb and later body weight
• the relationship between growth in infancy and blood pressure at age six.

And as with all our previous study waves, your consent is optional.

Research team

Principal Investigators

• A/Prof. Jeff Craig
• Prof. Richard Saffery

Associate researchers

• A/Prof. Marc Seal
• A/Prof. Tim Silk
• Dr. Alice Burnett
• Dr. Katrina Scurrah
• A/Prof. Christiane Theda

Project staff

• Dr. Jane Loke
• Dr. Pamela Leong
• Dr. Elisha Josev
• Ms. Kristal Lau
• Ms. Alicia Clifton
• Ms. Lada Staskova
• Ms. Anna Czajko
• Mr. Declan Bourke
• Mr. Matt Bisset
• Ms. Dinisha Parmar

Research postdoc

• Dr. Mihiri Silva 

Research students

• Ms. Deborah Ashley (PhD candidate)
• Ms. Taylor King (MD candidate)

Our research

Brain development study in twins

Brain development and thinking skills begin before birth and maturation occurs mainly between the ages of 7 to 11. Both genetics and environment influence it. With the data that we have collected during your pregnancy, it will allow us an important opportunity to examine the relationship between early life factors and mid-childhood brain development.

We have secured funding from the National Health and Medical Research Council (NHMRC) to invite all our twins who are turning 11 years old for a session of cognitive assessment.

An experience clinical neuropsychologist and families administered these assessments. For twins that are of the same sex, they are being invited for a brain scan using Magnetic Resonance Imaging (MRI).

Recruitment is scheduled to go on for 2.5 years (July 2018 till December 2020) and so far we have seen close to 40 families. If your twins have turned 11 and have not heard from us, please contact us as soon as possible, so that you do not miss out on this opportunity to take part in this exciting phase of the study.

Teeth and tooth decay

An important part of the previous phase of the study (6 years old) was examining the children’s teeth. We did this to not only see whether there was any tooth decay (holes in teeth), but also to see how the teeth were developing compared to the child’s age, by looking at what teeth had become wobbly or fallen out and how many permanent (adult) teeth had grown.

We also looked for any developmental anomalies (marks) on the teeth that may have occurred before the teeth came into the mouth or soon after. In addition, we examined the health of the gums and collected biological samples (dental plaque) from along the gum line. We are also interested in finding out more about healthy mouths and how this affects other parts of the body and lifestyles.

We found the prevalence of tooth decay was like that of the broader population. Of the twins who had their teeth examined, there were 57% of twin pairs who had no signs of tooth decay. There were 23% who both had tooth decay. In 18% of twin pairs, only one twin had tooth decay.

This is of particular interest as these twins have the same parents, were in the womb at the same time and are generally exposed to similar environmental influences such as maternal diet and lifestyle. Studying twins enables us to look at the potential strength of genetic influences (comparing fraternal and identical twins with and without tooth decay) and environmental influences, such as diet and tooth brushing. We already know there are many factors that can contribute to the risk of tooth decay.

These are mostly environmental influences such as diet and tooth brushing. Frequent snacking, particularly of sugary foods, brushing less than twice a day can all have an adverse effect on oral health.

What is not really understood is why two individuals who may have similar environmental influences result in one having tooth decay and not the other. In addition, there are a range of other influences that we don’t know a lot about, such as genetics and general health.

Tooth plaque

To better understand these influences, we collected and sent just over 940 dental plaque samples to our collaborators in the USA along with some fairly general information such as whether the twins were identical or fraternal, the children’s ages at the time of the sample collection, whether there was any tooth decay, how often the children cleaned their teeth and consumed sweetened foods or liquids.

From these samples, we sought to establish whether there is an association between tooth decay and distinct plaque microbial communities in both MZ and DZ twins and how this might change with the severity of tooth decay. We were also interested in to what extent genetic background could explain the microbiome patterns that are associated with tooth decay (comparing DZ twin pairs and MZ twin pairs) or environmental influences (tooth brushing, diet, general health).

What we have found so far

Although dental plaque microbial communities are partly controlled by host genetic factors, the genetic contribution seems to be more related to a healthy state than a diseased one (tooth decay). Our data also shows that factors specific to individual twins have a strong influence on oral health. This could mean that it is important to focus on individuals to prevent tooth decay. We are all different and so are twins! However, further research is planned using these samples to learn more about the genetic and environmental influences on oral health and disease.

Dental anomalies on tooth enamel

Many parents asked about the white or yellow marks on their children’s teeth that did not disappear with tooth brushing. These dental anomalies have occurred when the outer layer (enamel) of the tooth is developing, usually well before the tooth appears in the mouth. In some circumstances, affected teeth may be more sensitive or more susceptible to tooth decay. There are lots of theories about how this may have occurred (illnesses and infections of either the mother or infant during tooth development). We are also very interested in these anomalies and learning more about why they occur. By studying twins, and using the information we have already collected from before the children were born up to the present time, we can look more closely at influences.

From the dental examinations, we could discover that anomalies on the second primary molar (the very back baby tooth) were experienced by 68 children. Of these, there were 16 twin pairs where both children were affected and 36 pairs where only one was affected. More than half of all children had over one tooth with these anomalies. Of the children with these marks, 48 were fraternal and 17 were identical. There were three children affected whose zygosity is unknown.

​Publications