Jane Hansen
The Daily Telegraph
April 16, 2022
New research into the genetic secrets of how and why non-identical twins are conceived may unlock clues on fertility and offer future treatments for infertility.
But they need help from mothers of non-identical twins.
Identical twins occur when one egg and sperm form an embryo that splits into two identical embryos. It is thought to be sporadic and not genetic.
Non-identical twins happen when the mother releases two eggs in a single cycle and both are fertilised by separate sperm.
This is thought to have a genetic component, according to Professor Nick Martin from QIMR Berghofer Medical Research Institute. He is leading a new study into non-identical twins, also known as fraternal and dizygotic twins.
“The rate for identical twinning is about four per 1000 births and that is the same across all ancestry groups,” he said.
“Whereas non identical twinning is different. In Europeans it is about eight per 1000, so double the identical rate but in Africans it is about 20 per 1000 and in Asians about 2 per thousand.”
This led researchers to think there was a genetic component.
Prof Martin set up the Australian twin register in 1970 and noted families with lots of twins were always non-identical.
“You get families that are riddled with twins and it is always non-identical twins that run in families. Knowing that non-identical twins run in families, we’ve long wanted to find out what those genes are that are causing that,” Prof Martin said.
“We found two genes; the first one of those is in a gene called follicle stimulating hormone B and that has to be right, that is the gene we would expect.”
But there are plenty more genes he suspects play a role and the research needs a bigger sample of mothers of non-identical twins to discover more.
“We are after a much more detailed understanding of what controls ovulation in women and we think it will have implications for better contraception strategies and, in particular, better treatments for infertility,” he said.
“We strongly suspect in many cases in infertility in women, they are at the other end of the scale.
“My hypothesis is we will find women who are infertile, for female causes, not male causes, but women having trouble conceiving, are at the other end of the spectrum.
“We hope by having a detailed biological understanding of the pathway we might be able to prescribe better treatments, because IVF is only about a 20 per cent success rate for ovulation.”
Sarah Sufrin, 40, from Bondi Junction, gave birth to twin boys 17 years ago. Three more sons later, again fell pregnant with what she hoped would be a little girl – and she got double her wish.
“My twin boys were my first pregnancy and now I have twin girls who are now three,” she said.
“Because my twins are fraternal, non-identical, the genetic cause for that is on the mum’s side, it’s two eggs.
“All the twins in my husband’s family, including my mother-in-law who is an identical twin, has zero connection to my having twins because that is not how the biology works. It amuses me they all want to take credit for it.
“I do think there is a genetic link and I’d like to do my bit to contribute to it.”
To enrol go to: qimrberghofer.edu.au/nonidenticaltwinning.
