Page URL:

Two genes linked to higher chance of having twins

3 May 2016
Appeared in BioNews 849

A study has identified two gene variants that increase the likelihood of a woman having twins and could explain why twins appears to run in families. 

Using data contained in twins databases from the Netherlands, Australia and the USA, researchers at the Vrije Universiteit in Amsterdam compared DNA from over 2000 women who'd had twins with genetic information from 13,000 women who had not, and they identified a set of gene variants that might be associated with twinning.

They then sent their findings to a team in Iceland, which compared the results with their own dataset of 3500 mothers with twins and almost 300,000 controls to look for similarities.  

Two SNPs (single nucleotide polymorphisms) on the FSHB and SMAD3 genes emerged, which showed that if a mother had one copy of each the chances of having fraternal, or dizygotic, twins increased by 29 percent.

FSHB is the gene responsible for the production of follicle-stimulating hormone (FSH), which is involved in the menstrual cycle and which peaks just before ovulation. If FSH remains at high levels, it can result in more than one egg being released and an increased chance of twinning.

While the role of SMAD3 is more elusive, it seems likely that the gene affects ovarian response to FSH. If a woman's levels of FSH are normal, but her ovaries are more responsive to FSH because of a variant of SMAD3, this could also increase the likelihood of twinning. 

A genetic basis for twins has been assumed for some time from the patterns of twins that appear in families, but this research is the first to identify specific gene variants responsible.

'There's an enormous interest in twins, and in why some women have twins while others don't,' said Professor Dorret Boomsma, a biological psychologist at Vrije Universiteit and co-author of the paper. 'The question is very simple, and our research shows for the first time that we can identify genetic variants that contribute to this likelihood.'

The findings, published in the American Journal of Human Genetics, may offer some insight into the variance in implantation rates following IVF and into how multiple births, which are more common following IVF than natural conception, may be reduced in the future. Multiple pregnancies and birth present health risks for both the mother and child.

Currently, there is no way of knowing if a woman's ovaries will overproduce in response to the FSH hormone injected into the ovaries prior to IVF in order to stimulate egg production, but the researchers are now hoping to develop a genetic test to identify those women at risk of ovarian hyperstimulation, which is a dangerous side effect of IVF treatment.

Genetic Variations Help Make Fraternal Twins More Likely
npr |  28 April 2016
Having fraternal twins is in your genes—and in your hormones
Science (AAAS) |  28 April 2016
Identification of Common Genetic Variants Influencing Spontaneous Dizygotic Twinning and Female Fertility
American Journal of Human Genetics |  28 April 2016
Why Do Twins Run In Families? Two Genes Increase Mother’s Chance Of Giving Birth To Fraternal Twins
Medical Daily |  28 April 2016
Why fraternal twins run in families
Eurekalert (press release) |  28 April 2016
15 October 2018 - by Jamie Rickman 
The reasons why IVF treatment sometimes results in twin or triplet births – even though only one embryo is used – have been found by the largest study to date on single embryo transfer and multiple pregnancy...
25 April 2016 - by Dr Katie Howe 
Women with a mutation in the breast-cancer susceptibility gene BRCA1 may have reduced numbers of eggs left in their ovaries, according to a study led by Australian scientists...
15 February 2016 - by Dr Victoria Burchell 
The combination of increased use of fertility treatments and rising maternal age has caused a doubling in the rate of twin births in developed countries over the last 40 years...
17 August 2015 - by Kirsty Oswald 
Changes to the activity of cells in the ovary may contribute to poorer IVF success rates among women in their 40s...
8 June 2015 - by Ceri Durham 
Analysis of the genomes of thousands of women suggests that a woman's genes influence the age at which she first becomes a mother and the number of children she will have...
19 March 2012 - by Dr Lamiya Mohiyiddeen and Luciano Nardo 
IVF is a complex treatment for infertility requiring costly drugs and carrying significant risk of complications. Part of the procedure aims to stimulate the ovaries to produce more eggs, and conventional methods include a combination of hormones to induce follicle growth, from which eggs are collected...
to add a Comment.

By posting a comment you agree to abide by the BioNews terms and conditions

Syndicate this story - click here to enquire about using this story.