A large genome-wide association study of more than 560,000 people has identified 10 new genetic regions associated with the number of children we have during the course of our life, and the age at which we have our first child.
Nicola Barban et al identified ten new areas of the DNA sequence that are related with the age at first birth and the number of children ever born. Image credit: Vania Raposo.
Until now, human reproductive behavior was thought to be mainly linked to personal choices or social circumstances and environmental factors.
However, the new study shows that genetic variants can be isolated and that there is also a biological basis for reproductive behavior.
“For the first time, we now know where to find the DNA areas linked to reproductive behavior,” said study lead author Prof. Melinda Mills, from the University of Oxford’s Department of Sociology and Nuffield College.
“For example, we found that women with DNA variants for postponing parenthood also have bits of DNA code associated with later onset of menstruation and later menopause.”
“One day it may be possible to use this information so doctors can answer the important question: ‘How late can you wait?’ based on the DNA variants.”
“It is important to put this into perspective, however, as having a child still strongly depends on many social and environmental factors that will always play a bigger role in whether or when we have babies.”
The research shows that DNA variants linked with the age at first birth are also associated with other characteristics reflecting reproduction and sexual development, such as the age at which girls have their first period, when the voice breaks in boys, and at what stage women experience their menopause.
“Our genes do not determine our behavior, but for the first time, we have identified parts of the DNA code that influence it,” said study co-author Nicola Barban, also from the University of Oxford’s Department of Sociology and Nuffield College.
“This is another small piece to understanding this very large jigsaw puzzle.”
The authors calculated that variants in 12 DNA areas — 10 of which are new and 2 were previously identified in a study on age at first sexual intercourse — together predict less than 1% of the timing at which men and women have their first child and of the number of children they have in the course of their lifetime.
While these numbers seem ‘extremely small,’ their modeling shows that in some cases when the variants are combined, they can be used to predict the probability of women remaining childless.
Importantly, by examining the function of the DNA regions and the genes in these regions in detail, the team has identified 24 genes that are likely to be responsible for the effects of the 12 DNA variants on reproductive behavior.
Some of these genes were already known to influence infertility, while others have not yet been studied.
“An improved understanding of the function of these genes may provide new insights for infertility treatments,” said study co-authors Prof. Harold Snieder from the University of Groningen and Dr. Marcel den Hoed from Uppsala University.
The findings were published online this week in the journal Nature Genetics.
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Nicola Barban et al. Genome-wide analysis identifies 12 loci influencing human reproductive behavior. Nature Genetics, published online October 31, 2016; doi: 10.1038/ng.3698
