Starting one’s sex life and having children at a young age can run in the family. But can pregnancy have beneficial health effects and do the partner’s genes contribute to them?
- Text Ulla Kaltiala | Pictures Bettiina Lievonen, Jaakko Heiskanen and Mostphotos
“We are just beginning to understand how pregnancy affects health later in life,” says Associate Professor Taru Tukiainen.
Tukiainen is a researcher in the field of genetic epidemiology. One of her interests is studying what significance biological sex and reproductive history have for a person’s health.
Some people have genes that steer them more strongly towards reproduction: They may have early puberty, begin their sex life at a young age, and have children from an early age and in large numbers. “There are various reasons behind this, including genetic factors related to personality traits such as risk-taking and willingness to experiment, as well as other biological mechanisms related to brain and hormonal functions,” Tukiainen explains.
The same factors may partly explain the connections discovered between early sexual experiences and issues such as later mental health problems. Meanwhile, early puberty and giving birth at a young age have been linked to a heightened risk of cardiovascular diseases and type 2 diabetes.
“On the other hand, it is evident that becoming a mother at a young age and having more children provide protection against breast cancer. This appears to be linked with the changes that occur in breast tissue during pregnancy and breastfeeding.”
Each pregnancy also changes the structures of a woman's brain. “Changes have been observed in various parts of the brain, such as parts related to the regulation of attachment.”
During pregnancy, the genomes of the mother and the foetus interact in a unique way.
Taru Tukiainen
Nausea during pregnancy may be caused by the genes of the foetus
“During pregnancy, the genomes of the mother and the foetus interact in a unique way,” Tukiainen explains. She is researching the topic in a project funded by the Research Council of Finland.
The genes of a foetus may affect how the pregnancy progresses. For example, one factor contributing to hyperemesis is a gene variant that increases the production of the GDF15 hormone in the placenta. If only the foetus has this gene variant, the mother may experience severe nausea due to not being accustomed to the large amounts of the GDF15 hormone. Vomiting might continue throughout the pregnancy and require hospitalisation.
About two per cent of all pregnant people suffer from hyperemesis. Pre-eclampsia is a slightly more common condition. Researchers have also discovered connections between pre-eclampsia and foetal genes that affect the functions of the placenta.
A foetus receives half of its genes from its father, who may thereby contribute to the mother’s risk of pregnancy complications. “It would be nice to have a simple genetic test for determining the suitability of a partner. However, the risks really cannot be predicted in a straightforward manner,” Tukiainen notes.
However, the idea that opposites complement each other seems to be true to some extent. “For example, if the immune system’s HLA genes are sufficiently different between the mother and the father, the chances of a successful pregnancy are higher.”
A mother’s lifestyle and other events during pregnancy can also affect the child’s later health in many ways. However, recent research indicates that some of these connections can actually be explained by the shared genes of the child and the mother. “One example of this is low weight at birth, which has been linked to the risk of heart disease later in life. Our recent research showed that certain factors in the mother's genes can not only impair the child’s growth in the uterus but also increase the risk of heart disease if inherited by the child. In other words, growth conditions in the uterus contributing to low weight are apparently not the main risk factor.”
According to Tukiainen, there is a growing awareness of the interactions between the genomes of the mother and the foetus, but more detailed examination requires research data that contain genome and diagnostic data on both the children and their parents. “Various projects collect family analysis data. One of these is the Norwegian MoBa project, with which we cooperate. In Finland, data from the national FinnGen project is available for research.”
Less pregnancies – more autoimmune diseases?
During pregnancy, the foetus is in contact with the mother through the placenta. “It is rather exciting how a woman’s body accepts a foreign organ with another human's genotype and sustains its growth for nine months,” Tukiainen says.
This is possible because the woman’s immune system adapts to the pregnancy. The functioning of the immune system actually has various differences between the sexes, and reducing the number of pregnancies may affect these differences.
“Autoimmune diseases are more common among women, whereas men are more susceptible to infectious diseases. One contributing factor for this difference may be the fact that the female body develops to have multiple pregnancies from a young age. Some theories state that the risk of autoimmune diseases increases in modern societies due to a lack of repeated pregnancies and pregnancy-related hormonal changes.”
Tukiainen points out that these findings do not indicate a need for having more babies; rather, the research can help produce new ways for preventing health problems.
There are various other differences in morbidity between men and women, and sex hormones contribute to these differences. For example, men develop heart diseases at a younger age, while women are protected from heart diseases by oestrogen until they reach menopause. Parkinson's disease is also more common among men. On the other hand, women are more often diagnosed with depression, varicose veins and Alzheimer's disease. This may partly be explained by the fact that women have a lower threshold for seeking medical attention and live longer.
Women also experience prolonged pain more often than men. “In addition, animal studies have indicated that the mechanisms of chronic neuropathic pain may differ between the sexes. This could also be significant when planning treatment,” Tukiainen explains.
When X chromosome genes refuse to stay quiet and Y chromosomes disappear
Researchers have become increasingly interested in studying the connections between sex chromosomes and health. Women have two X chromosomes, one from the mother and one from the father, whereas men inherit an X chromosome from the mother and a Y chromosome from the father. Sex chromosomes were previously considered important mainly for determining biological sex and for causing rare diseases, such as bleeding disorders, through defective X chromosome genes that boys inherit from their mothers. “However, the X chromosome contains many genes and gene regions connected to multifactorial diseases.”
Both men and women should only have one active X chromosome, as gene regulation mechanisms in women make one of the X chromosomes inactive. “However, about a quarter of the X chromosome’s genes seem to evade this inactivation, leading to excessive amounts of their produce in a woman's body. We do not yet fully understand why this happens and how this contributes to health inequalities. Ageing may further weaken the inactivation of the X chromosome, but this has so far only been studied with mice.”
On the other hand, one specific haplogroup of the Y chromosome increases the risk of heart disease among men even when no other risk factors are present. “This was previously shown in British research, and our own research showed the same results in the Finnish population.”
“It is also quite common for the Y chromosome to begin disappearing from men’s blood cells as they grow older. More than 10% of cells can lack the Y chromosome, and studies have linked this to higher risks of heart attacks and Alzheimer's disease,” Tukiainen explains.
