A joint study by the Australian Twin Registry at the University of Melbourne, and the Murdoch Childrens Research Institute has found that 32% of parents of identical junior twins were unsure or incorrect about their twins' genetic identity or zygosity.
When it came to non-identical pairs, 29% of parents were incorrect or unsure, the paper Why Accurate Knowledge of Zygosity is Important to Twins published in Twin Research and Human Genetics said. When combining adult twin responses with junior twins, 27% of all twins in the study were incorrect or unsure of their zygosity.
"We found a substantial proportion of parents and twins had been misinformed by their own parents or medical professionals," Associate Professor Jeff Craig of the University of Melbourne's Australian Twin Registry and Senior Research Fellow, Early Life Epigenetics Research Group at the Murdoch Childrens Research Institute said.
The study investigated the accuracy of genetic identity of junior and adult twins, and whether knowing zygosity was important to twins. The study provided such strong evidence that twins knowing their true genetic identity provided with peace of mind and positive emotions. In fact so much so that Associate Professor Craig suggested that medical professionals universally recommend genetic testing of same-sex twins as early in life as possible.
He also believes that medical professionals, twins and their families should receive increased education about zygosity issues. He said such knowledge can have implications for the bonding of twins, including tissue compatibility in organ transplantation, assessing disease risk, the personal right to know one's identity, and estimating the likelihood of the mother or close relatives giving birth to further sets of twins.
The human story: Sue Sukkel of Melbourne, Australia, who was incorrectly told her twins were non-identical
"Are you identical or not?" is a question constantly faced by many twins throughout their lives and can cause considerable angst, according to a new study.
While it may seem a benign question to non-twins, for twins who are not sure if they are identical or not, or have been misled - and surprisingly there are many - it can have considerable significance for their physical and mental wellbeing.
Mother of eight-year-old twins Sue Sukkel participated in the study and has first-hand experience of the impact of twin identity confusion. She had always believed her twins, Lilly and Abbie, were non-identical after being told so at their birth in hospital by the doctor and midwife - although a lingering doubt persisted because the girls looked so similar.It wasn't until she attended a twins' festival many years later where free genetic testing was on offer that she decided it was time to address the uncertainty.
"When the results arrived in the mail advising they were identical, I was so overwhelmed that I burst into tears," Sue said. "I was so pleased to have my real 'inner gut' feelings confirmed and pleased that the girls will grow up with this knowledge. As an adopted child myself, I know what it is like to be unsure about your genetic heritage and how that can affect you."
Associate Professor Jeff Craig of the University of Melbourne's Australian Twin Registry and Senior Research Fellow, Early Life Epigenetics Research Group at the Murdoch Childrens Research Institute said the confusion often arose due to wrong assumptions that identical twins always share a placenta in the womb and always look and behave identically. But nearly one-third of identical twins (as in the case of the Sukkel twins) and all same-sex non-identical twins have separate placentas.
To add to the confusion, twins with separate placentas can be implanted so closely together in the womb that the placentas appear to 'fuse'. To the naked eye it looks as if there is a single placenta.
Identical twins can also look and behave differently, particularly as they age. The only way to know for sure whether same-sex twins are identical or fraternal is to have a DNA fingerprint (zygosity) test done. Genetic testing is usually done by collecting a mailed kit with a cheek swab.
"It is interesting how that initial wrong advice played out in our lives," Sue Sukkel said. "I used to tell my family and friends, 'you are crazy to think the girls are identical', as I was so convinced they weren't. The girls were teased and embarrassed at school because they would argue they weren't identical and their class mates didn't believe them," Sue said. "In the end, I think it is important to know the truth and to have certainty for the girls and our family. As they say, knowledge is power," she said.