Genetics Plays Important Role in Age at First Sex and Birth

Summary: Researchers have identified 371 genes, eleven of which were sex-specific, linked to the timing of when a person first has sex and the point of life they are most likely to become parents.

Source: Oxford University

An Oxford-led team, working with Cambridge and international scholars, has discovered hundreds of genetic markers driving two of life’s most momentous milestones – the age at which people first have sex and become parents.

In a paper published today in Nature Human Behaviour, the team linked 371 specific areas of our DNA, called genetic variants (known locations on chromosomes), 11 of which were sex-specific, to the timing of first sex and birth. These variants interact with environmental factors, such as socioeconomic status and when you were born, and are predictors of longevity and later life disease.

The researchers conducted a Genome-Wide Association Study (GWAS), a search across the entire human genome, to see if there is a relationship between reproductive behaviour and a particular genetic variant. In the largest genomic study ever conducted to date, they combined multiple data sources to examine age at first sex (N=387,338) and birth (N=542,901) in men and women. They then calculated a genetic score, with all genetic loci combined explaining around 5-6% of the variability in the average age at sexual debut or having a first child.

Professor Melinda Mills, Director of the Leverhulme Centre for Demographic Science at the University of Oxford and Nuffield College, and the study’s first author says, ‘Our study has discovered hundreds additional genetic markers that shape this most fundamental part of our lives and have the potential for deeper understanding of infertility, later life disease and longevity.’

The genetic signals were driven by social factors and the environment but also by reproductive biology, with findings related to follicle-stimulating hormone, implantation, infertility, and spermatid differentiation.

Professor Mills adds ‘We already knew that childhood socioeconomic circumstances or level of education were important predictors of the timing of reproduction. But we were intrigued to find literally not only hundreds of new genetic variants, but also uncover a relationship with substance abuse, personality traits such as openness and self-control, ADHD and even predictive of some diseases and longevity .’

This shows a pregnant woman
Hundreds of genetic drivers affect sexual and reproductive behavior. Image is in the public domain

Professor Mills says, ‘We demonstrated that it is a combination of genetics, social predictors and the environment that drives early or late reproductive onset. It was incredible to see that the genetics underlying early sex and fertility were related to behavioural dis-inhibition, like ADHD, but also addiction and early smoking. Or those genetically prone to postpone sex or first birth had better later life health outcomes and longevity, related to a higher socioeconomic status in during childhood.’

Genetic factors driving reproductive behaviour are strongly related to later life diseases such as Type 2 diabetes and cardiovascular disease.

‘It is exciting that the genetics underlying these reproductive behaviours may help us understand later life disease.’

Professor Mills concludes, ‘Starting your sexual journey early is rooted in childhood inequality but also has links with health problems, such as cervical cancer and depression. We found particularly strong links between early sexual debut, ADHD and substance abuse, such as early age at smoking. We hope our findings lead to better understanding of teenage mental and sexual health, infertility, later life disease and treatments to help.’

Funding: Funding was provided to M.C.M. by the European Research Council, SOCIOGENOME (615603), CHRONO (835079), ESRC/UKRI SOCGEN (ES/N011856/1), Wellcome Trust ISSF, Leverhulme Trust and Leverhulme Centre for Demographic Science, to N.B. by ERC GENPOP (865356), to F.C.T. by LabEx Ecode, French National Research Agency (ANR) Investissements d’Avenir (ANR-11-LABX-0047), to M.d.H. by Swedish Heart-Lung Foundation (20170872, 20200781, 20140543, 20170678, 20180706 and 20200602), Kjell and Märta Beijer Foundation and Swedish Research Council (2015-03657, 2019-01417). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

About this genetics and reproduction research news

Source: Oxford University
Contact: Press Office – Oxford University
Image: The image is in the public domain

Original Research: Closed access.
The study, Identification of 371 genetic variants for age at first sex and birth linked to externalising behaviour” by Melinda C. Mills, Felix C. Tropf, David M. Brazel, Natalie van Zuydam, Ahmad Vaez, eQTLGen Consortium, BIOS Consortium, Human Reproductive Behaviour Consortium, Tune H. Pers, Harold Snieder, John R. B. Perry, Ken K. Ong, Marcel den Hoed, Nicola Barban & Felix R. Day. Nature Human Behavior


The study, Identification of 371 genetic variants for age at first sex and birth linked to externalising behaviour

Age at first sexual intercourse and age at first birth have implications for health and evolutionary fitness.

In this genome-wide association study (age at first sexual intercourse, N = 387,338; age at first birth, N = 542,901), we identify 371 single-nucleotide polymorphisms, 11 sex-specific, with a 5–6% polygenic score prediction. Heritability of age at first birth shifted from 9% [CI = 4–14%] for women born in 1940 to 22% [CI = 19–25%] for those born in 1965. Signals are driven by the genetics of reproductive biology and externalising behaviour, with key genes related to follicle stimulating hormone (FSHB), implantation (ESR1), infertility and spermatid differentiation.

Our findings suggest that polycystic ovarian syndrome may lead to later age at first birth, linking with infertility. Late age at first birth is associated with parental longevity and reduced incidence of type 2 diabetes and cardiovascular disease. Higher childhood socioeconomic circumstances and those in the highest polygenic score decile (90%+) experience markedly later reproductive onset.

Results are relevant for improving teenage and late-life health, understanding longevity and guiding experimentation into mechanisms of infertility.

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