- Researchers examine several large twin cohort studies for trends in DNA
- They found that identical twin DNA had consistent signatures
- While 12 percent of pregnancies begin as multiples, only 2 percent end up being
- It can be used to identify whether someone was an identical twin in the womb, even if their sibling was never born or developed in the womb
It’s a mystery that has puzzled scientists for years – why are some twins born identical and others not?
Although it was long believed that identical twins occur at random, a new study suggests that is not actually the case.
Instead, researchers from the Vrije Universitt in Amsterdam claim it to be a ‘signature’ in their DNA, which persists from conception to adulthood.
About 12 per cent of pregnancies begin as a multiple, but only two per cent of both babies end up with – a condition known as ‘vanishing twin syndrome’.
Until now it was believed that the appearance of identical twins, which rarely run in the family, was completely random, but the team says it depends on their DNA.
The authors say this DNA signature allows them to identify whether a person was conceived as an identical twin, even though they are known to be twins.
They cannot yet say when these signatures appear, and therefore need to investigate further whether they are inherited from a parent or appear randomly when the egg hatches.
Scientists may be closer to finding a solution to the long-standing mystery of why some twins are born alike, and it is down to a ‘signature’ in their DNA. stock image
Twins are two individuals that are formed in the same uterus.
Fraternal Twins (Non-identical)
Two eggs are fertilized by two sperm and both are implanted into the walls of the uterus at the same time.
These eggs are produced in separate, separate sacs adjacent to each other and share 50 percent of their DNA in the same way as non-twin siblings.
They can be of different sexes, although most are same-sex twins and they tend to run in families.
A single egg is fertilized by a single sperm and becomes embedded in the wall of the uterus, but at some point, it splits into two from a zygote.
Most identical twins separate within eight days of conception.
They rarely run in families and there is evidence for common markers found in identical twin genomes.
Jenny van Dongen, Doret Boomsma and their colleagues studied large international twin groups to identify signatures in DNA that were specific to identical twins.
Researchers discovered 834 points in the genome of identical twins, who were born after a fertilized egg split into two embryos.
They say this measurement of DNA can be used to determine whether someone was an identical twin with 80 percent accuracy.
This would help them identify those who had lost twins in the womb, or were separated from twins at birth.
The team can’t yet say whether there are DNA markers as to why someone is an identical twin, or whether they occur after the random splitting of a fertilized egg.
However, evidence of genetic markers specific to identical twins may help treat congenital disorders that disproportionately affect that group, including spina bifida.
To find the markers, the team scanned the DNA of more than 3,000 identical twins using blood and cheek cell samples, and compared them to the twins.
Altogether they examined 400,000 locations in each individual’s genome.
This allowed them to find 800 locations that had differences in methylation.
It is an important process involved in protecting and repairing DNA as well as generating energy and preventing cancer.
Researchers explain that finding differences in so many places is what separates identical twins from all others.
Van Dongen explained, ‘It is possible that something is established very early, which propagates to later cells. Science.
Some of the changes made sense to the researchers, as they confer tags on genes involved in cell adhesion that can affect the division of an egg into two.
Other changes, including some at the ends of chromosomes, don’t make sense, as they are linked to aging – but identical twins have the same lifespan as non-twins.
Identical twins have a unique DNA signature that persists from conception to adulthood, said experts from Vrije Universitt in Amsterdam, Netherlands. stock image
More extensive research will be needed to determine whether these changes are caused by the splitting of the egg, or are from the beginning.
Nancy Pedersen of the Karolinska Institutet, not involved in the study, told Science that the findings ‘offer fascinating insights into possible mechanisms [identical] ‘Twining’ which may shed light on rare disorders associated with genetic alterations.
Another use of this would be in determining whether there was ever a twin – eg, in some cases a ‘fading twin’ will appear on an ultra sound, but in many cases it is absorbed without leaving a trace.
The findings have been published in the journal nature communication.
Looking double? One in every 42 babies born is now twins due to the rise in IVF and artificial insemination
According to a new and comprehensive global study, more human twins are being born than ever before.
Since the 1980s, the rate of twins per 1,000 deliveries has increased by a third from 9 to 12, meaning that there are approximately 1.6 million twins born each year worldwide and one out of every 42 babies born. There is a twin.
A major reason for this growth is the increase in medically assisted reproduction (MAR) including in vitro fertilization (IVF), ovarian stimulation and artificial insemination.
Another reason for the increase is the delay in pregnancy for women in many countries over the past decades – the chances of having twins increase with age.
Women near menopause experience hormonal changes, which can encourage their bodies to release more than one egg during ovulation.
About 80 percent of all twins…