Having fraternal twins is in your genes!

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Researchers have found evidence that the reason behind having fraternal twins could be a bunch of genes.

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Twins, Credit: Pixabay

Any parent of fraternal twins who does not have a history of twins in their family often wonders why they had twins! Of course, the happiness is double as are their bundles of joy but this question does nag them initially. And if you are someone who is curious and knows a little about genetics, it’s highly likely that you have given this a thought too.

Turns out it’s in the genes of the mother. While there has been a lot of research happening to find out the similarities and differences between identical and fraternal twins, there isn’t much going on around fraternal twins alone since they are not genetically identical as the identical twins. But there has been rising speculations amongst the researchers since the US saw an increase in twin births increase by a factor of 1.9 between 1971 and 2009. The general observations were that mothers who were older or conceived through fertility treatments gave birth to fraternal twins. But the exact scientific basis for why this happened was unknown.

So, a group of molecular geneticists from Vrije Universiteit led by Hamdi Mbarek carried out a genome-wide association study in mothers of fraternal twins to check if there are any genetic familiarities and test their significance across a broad range of female fertility and reproductive traits. They used three twin registers from Netherlands, Austria and Minnesota (US) which had detailed information about the mothers of fraternal twins and their genotype data and compared it with the other mothers’ data. They specifically looked for Single Nucleotide Polymorphisms (SNPs) that were present in mothers of fraternal twins only.

Surprisingly, they found two such SNPs. One is associated with the follicle stimulating hormone (FSH) the other is associated with how ovaries respond to FSH. FSH plays a crucial role in the production and maturation of eggs in ovaries. If the FSH levels remain high for a prolonged period of time, multiple eggs are released which increases the chances of conceiving fraternal twins. As for the other SNP, at least in mice, it influences how ovaries respond to FSH thereby shedding more light on why women who go for in-vitro fertilization have higher chances of having fraternal twins.

Apart from catering to the general curiosity, this study has opened a new world of possibilities in reproductive medicine. Having twins is associated with morbidities such as preterm birth, discordant twin growth, preeclampsia, postpartum haemorrhage, etc. leading to further complications in the mothers.

By defining the genetic basis of fraternal twinning in the general population it has opened doors to improved outcome prediction and novel fertility treatments which could be a boon for the mothers’ health worldwide.

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To download the original paper, click here