Tasmanian twins don't just have a special bond with one another, but the chance to make a special contribution to medical research.
Identical twins, with their matching genes, have helped extricate the environmental influences from the genetic in Australian medical research for decades.
Subjects for the vital research are sourced through the Australian Twin Registry, established in 1981 with support from the National Health and Medical Research Council.
Registry director John Hopper said identical and non-identical twins gave researchers a perfect set of test subjects, with closer matching variables that would otherwise be sourced through the general public.
He said longitudinal studies that follow twins for life helped better inform medical research.
``Twin studies are providing insights on what it is to be human, insights into the environment and how genes influence our health and our behaviour,'' Professor Hopper said.
``When you have identical twins, they share all their genes so you have a chance to see similarities in their health, blood pressure, bone strength and risk factors in disease.
``Looking at the differences and similarities between genetically identical and fraternal twins gives insights into the roles that genes play and explains why humans differ on all sorts of characteristics and diseases.''
He said twins gave medical researchers ``double the value''.
``The twin design is very powerful scientifically and it gives clearer answers,'' Professor Hopper said.
``It also makes medical studies much cheaper as you are focusing on the key people that can give information.''
Professor Hopper has published more than 480 papers that analyse twin and family data.
His twin research has involved investigating breast, colorectal prostate and childhood cancers, melanoma and asthma.
He said another study linked bone density depletion with smoking, where researchers found a twin who had smoked over 20 years had 5 per cent weaker bone density than the non-smoking twin, making them twice as susceptible to osteoporotic fracture.
Twins worldwide have long claimed an ability to telepathically communicate with the other or have other physic connections, such as the ability to feel the other's pain.
Professor Hopper said while the National Health and Medical Research Council facilitates research specific to only twins, no research has been conducted to scientifically validate either claims. ``We only know what they tell us,'' he said.
``Last year, we did have a pair of twins in a study which involved a scan of the brain.
``One of the twins had headaches but we found that the twin that didn't have headaches actually had a brain cancer. ``As a result, he was operated on and his life was saved.''
Tasmanian twins are needed this year for studies involving epilepsy, atrial fibrillation and the National Assessment Program for Literacy and Numeracy.
To place your name on the Australian Twin Registry, call 1800 037 021 or visit www.twins.org.au
FACTS ABOUT TWINS:
Identical twins share 100 per cent of their genes while fraternal twins, or non-identical twins, share 50 per cent of their genes.
Identical twins occur when one female egg is fertilised by one sperm and then separates. Fraternal twins occur when two eggs are fertilised.
The Australian Twin Registry has about 37,000 identical and fraternal twins of all ages on its register. Professor Hopper said this represented one-in-six twin pairs in Australia.
Twins represented 16.7 of 1000 Australian births in 2010. This was up by 1.5 births from 2001.