The uniqueness of twins is important when it comes to finding out about our health
Written by Jenny Boadle from the Twins Research Australia and published in the AMBA Magazine
It is often the similarities of twins that draw attention and interest from people. But for health and medical experts it is the differences between twins in a pair that are the most fascinating. This is because they offer important clues about how our genes and environment contribute to our health and wellbeing.
Genes versus lifestyle
Twins share so many things − same parents, same time of conception, same environment before and after birth and, for identical twins, the same genes. Therefore, when one twin develops a disease but the other doesn’t, or one twin experiences a lifestyle or event that is completely different to the other, researchers can learn valuable information about how the environment shapes us. They can do this by matching for genes and all those other things shared by twins. The uniqueness of each twin individual tells us that our genes are not our destiny. Our genetics are not ‘blueprints’ but rough guides about what makes us human. It also tells us that the environments shared by twins − the womb, family life, school life − are also not their destiny.
Power to identical and non-identical
Although differences between identical twins provide very important clues for our health and wellbeing, non-identical twins are just as important. The most powerful twin studies gather information from both identical and non-identical twin pairs and compare similarities between twins in a pair, and across different twin pairs, to find out if there is evidence for genetic factors in disease development.
So in what research areas have twins made a difference?
You may be surprised to learn of the incredible diversity of twin research and the many health discoveries made possible thanks to twins.
The genetics of epilepsy
Epilepsy is not one disease, but a large number of different conditions that can be categorised into groups. By looking at the similarities and differences of identical and non-identical twins, epilepsy researchers over the past 30 years − led by Prof Sam Berkovic and Prof Ingrid Scheffer at the University of Melbourne – have discovered which groups of epilepsy conditions are likely to have a genetic basis.
This research was the first step in identifying more than 20 different epilepsy genes which, when altered (otherwise known as mutated), can result in an inherited form of epilepsy. Understanding these genes gives insights into the biological mechanisms underlying hereditary epilepsy, which in turn helps to understand causes, diagnosis and appropriate treatment. The uniqueness of twins as individuals is also contributing to current knowledge in the areas of speech and language, autism and education.
Speech and language disorders
Speech and language disorders have a significant impact on children’s development, self-esteem and learning. There is strong evidence from studies of twins that over 90% of speech and language disorders have a contribution from defective genes. These defective genes can be passed on in families, and sometimes they are present in twins. Little is known about the genes contributing to speech production apart from one gene discovered in a large family with very severe speech impairment. The researchers believe most defective genes newly arise in individuals with speech and language disorders, and twins can help them find these genes.
This research is recruiting rare identical twins where only one twin of each pair has a speech and language disorder. The research team aims to find out more about the defective gene by looking at the differences between the twin with a speech and language disorder and the one without. The researchers also aim to take detailed pictures of the brains of the twins to try and understand how our brains develop speech and language, and how defective genes can damage these processes.
Discoveries in this relatively new area are likely to provide huge advances and fill major knowledge gaps in our understanding of speech and language. Understanding the causes is the essential first step towards targeted therapies and improved treatment for children with these disorders.
Twins and autism
The aim of the study is to look at the similarities and differences in brain structure and function in identical twins where one has been diagnosed with an Autism Spectrum Disorder (ASD) and one has not, and also where both twins in a pair have a diagnosis.
ASDs are a cluster of neurodevelopmental conditions associated with core differences in social communication, social interaction, and restricted and repetitive behaviours. Although it is known that differences in brain structure and function play a role in the development of ASD, there are many questions around how and also what parts of the brain are involved. Information gathered in this study will provide new knowledge to better understand the diverse nature of ASD.
Influences on a child’s education
In this longitudinal study, researchers aim to identify the influence of genes, family and school environment on how well a child performs in the National Assessment Program: Literacy and Numeracy (NAPLAN) tests. Twins, higher older multiples and siblings have participated by giving permission for their NAPLAN scores to be accessed by the researchers and also through the completion of a questionnaire. Identical twins who have differing educational outcomes have contributed significantly to this study as they have enabled the researchers to identify the role played by non shared environments (such as different teachers, different classmates and different friendship groups).
Through this work the researchers hope to learn about the best ways to foster academic development in the crucial mid-school years. They also hope to contribute to public debate about the role of teachers and schools in a child’s academic progress, and to public policy development.
When one twin smokes, the other usually does too. But there are some twin pairs who differ substantially in their smoking habits. In the 1990s, Prof Ego Seeman and Prof John Hopper identified 20 female pairs in which one twin had never smoked and the other had smoked for more than 20 years. They found that the bones of the smoking twin were less dense than those of their twin, with the difference being significant enough to double their risk of an osteoporotic fracture in later life. This provided compelling evidence that smoking causes osteoporosis.
If you are interested in any of the studies from this article, please email firstname.lastname@example.org or freecall 1800 037 021. To find out more about how twins contribute to research visit the Twins Research Australia website.