Image Caption: Sisters Kathleen Byrne and Barbara Setterfield are involved in the Older Australian Twins Study. Photo: Pat Scala
Identical twins Kathleen Byrne and Barbara Setterfield are prized scientific test subjects.
That is because, by sharing 100 per cent of their genes, the sisters provide unique living clues to answering a hotly-debated question.
Do genetics or lifestyle choices have the greatest impact on people's health?
Although most of their experiences have been enjoyable, the professed junk-food lovers still complain about the week they were put on a salt-free diet.Throughout their adult lives Kathleen and Barbara have been measured, tested and integrated by a great line-up of researchers. They estimate they have been part of about 50 twin studies over the past three decades.
"The only lollies you could have were Cherry Ripes," Barbara said. "That was a horrible one."
Now aged 70, the Melbourne twins are taking part in a special study investigating healthy brain ageing – the largest and most comprehensive project of its kind ever undertaken in Australia.
The Older Australian Twins Study has involved 623 twins, triplets and siblings aged 65 and older, including 220 people from Victoria.
Researchers at the Centre for Healthy Brain Ageing say since the study begin in 2007 they have used the data to make a number of important findings, which point to a combination of genetic and environmental causes of age-related disease.
Chief investigator Perminder Sachdev said they have found strong "genetic influences" on whether someone would develop small vessel disease in the brain, a condition which has been linked to dementia, depression and cognitive decline.
He said they also found some of the chemicals in the brain were influenced by genetics, although there was still uncertainty on what genes were involved.
"Of course, the twin studies also suggest that there are significant environmental influences on all these features, which means that the brain can be modified in both structure and function through environmental intervention," Professor Sachdev said.
And in many cases it is not possible to separate the environmental and genetic causes of age-related disease, he said, as small genetic dispositions could be triggered by environmental factors such as smoking and obesity
Meanwhile, the study has also resulted in some unexpected personal findings, due to volunteers undergoing rigorous medical testing, including MRI scans, DNA extraction and psychiatric assessments.
Three cases of dementia have been diagnosed in Victorian twins and in 2009 a scan revealed a fast-growing brain tumour in volunteer Brian Hay, who had previously showed no symptoms of ill health. Doctors later told Mr Hay if the tumour had not been discovered as part of the study testing it would have been "too late".
Christel Lemmon, from the National Ageing Research Institute, has been visiting twins across Victoria for seven years to collect the data for the study. She said identical twins often shared a very strong connection, with some claiming they could sense when their sibling was sick or injured.
However she still believes individuals have the power to control much of their own health. "Not everything is genetic," Ms Lemmon said.
"There was one lady who has always been sporty and her sister was getting dementia and she wasn't," Ms Lemmon said. "I just said to her 'keep doing everything you've been doing'."
Kathleen and Barbara have a similar theory on the power of genetics. Kathleen – a smoker of 55 years - recently had a heart attack, while her Barbara sister who has never regularly smoked did not.
"I'm me and she's her," Kathleen said. "I have had three kids, she's had two. I had a lot of operations, she's had none."
"We're similar but when your environment changes you process everything differently."
Published in theage.com.au