Your Genes Can Remember What Your Grandparents Had Been Through
The challenging life of your (grand)parents may leave scars on your genes.
In the winter of 1944, Dutch people were having a grueling time since food transport from Germany halted due to a conflict between the Nazis and Dutch during the World War II. By the time the German occupation ended in May 1945, more than 18,000 people had died of starvation. This tragic event has gone down in history as “The Dutch Hunger Winter”.
The pregnant women were maybe the worst affected among the population. They failed to gain the weight that they were supposed to, and their children were mostly born underweight and unhealthy, which have been expected. But the story is getting more interesting after this. The children of these starved women became overweight as they grew up. They also developed high cholesterol, obesity, diabetes, addiction, and even schizophrenia later in life.
When these people have kids, those were also affected by the same problems, developing diabetes, and obesity. The unfortunate life of their grandparents influenced their health. Was this just a coincidence? How is it possible that scars of the famine can be seen even in the second generation? Science has an answer for that: Epigenetics.
Epigenetics is the study of modifications that can change the way your genes work, without changing your DNA sequence. Thus, epigenetic changes don’t affect our genetic code as mutations and deletions in DNA do. To be able to explain it in a detail, we might need to refresh our high school biology knowledge and remember what DNA, RNA, and protein are.
DNA is our unique genetic code, a recipe book to produce our proteins. Our body first makes RNA from DNA before producing proteins. You can think of RNA as a scratch paper written by using our DNA book, containing notes and instructions about how to produce a specific protein. Proteins are critical molecules for the structure, function, and regulation of our bodies.
If a certain gene in our DNA is more active, it means that the gene will be more available to make more RNAs, and eventually more of a specific protein. What makes a gene more or less active is mostly nothing more than a molecule on the genes or proteins covering our genes. As an example, a methyl group binds to certain places in DNA and makes it, generally, less active, meaning that the protein synthesis for this gene decreases. It is an epigenetic mark called ‘DNA methylation’.
Environment is the biggest parameter influencing our epigenetic structure. Environmental factors include but are not limited to pathogens, stress, diet, and exercise. For example, you might have good genes that lower your risk to develop certain diseases, but your bad diet can alter the epigenetic marks on your genes, making you more susceptible to get that disease later in life.
We all come from a single cell. Our cells keep dividing by replicating the same DNA and specialize to form tissues and organs as we grow in our mother’s womb. How do they know that they will be a part of our skeletal, digestive, or immune system even though they all share the same genetic code? The answer is, again, epigenetics.
As the fertilized egg in the mother’s womb divides and produces more cells, epigenetic marks start to appear. Remember, the environment influences the epigenetic structure, and the mother’s belly is the very first environment a fetus is exposed to. Although all cells are identical in terms of DNA sequences, these marks decide which proteins and how much protein are produced, resulting in cell differentiation, tissue, and organ formation.
Now, how did we get here? Ah, it’s the Dutch Hunger Winter. The famine, which left mothers malnourished during pregnancy, negatively affected the environment, hence, the epigenetic structure of the babies in their bellies. Thus, the babies’ protein synthesis became different from their healthy counterparts, rendering them susceptible to develop certain diseases later in their lives.
However, this only explains why the children of the mothers were affected by the famine. What about the grandchildren? How could they still feel the impact of the famine?
Some of the epigenetic marks can be inherited to the next generations. Principally, all epigenetic tags are erased during egg and sperm production in parents so that the zygote doesn’t have any in the beginning. However, some epigenetic marks can escape from this deletion process and transmit themselves to the zygote. That’s how the grandchildren of people who faced the famine were affected, the inheritance.
It should make more sense of how a period of starvation could impact two generations. But it might bring new questions to mind. Are these epigenetic marks only be inherited by mothers during pregnancy? No, male sperm can also carry and transfer those marks to the next generation.
Interestingly, a study shows that the children of malnourished fathers during the Dutch famine, but not mothers, became heavier and even obese. It indicates that both the environment in the mother’s belly and the father’s sperm are the factors determining epigenetic marks in the baby’s genes in case of malnutrition.
Nutrition is not the only factor influencing epigenetic marks that could be inherited. A study reports that mice that are exposed to stress during pregnancy transmit stress-related social defects to the two next generations. Besides, nicotine exposure of rats leads to asthma in the offsprings up to three next generations. Environmental toxicity and exposure to chemicals also increase the risk of infertility, cancer, obesity, and anxiety-like behaviors in the next generations via inheritance of epigenetic marks.
The Dutch Hunger Winter remarkably showed how parents’ life can influence the life quality of their children and grandchildren. The epigenetic structure is dynamic and can adapt to the changing environment in contrast to the DNA that is more stable and resistant to alterations. The body recognizes the current environment and changes its functioning by altering the epigenetic marks on the genome. This is mostly beneficial for the individual itself. However, it may be harmful to the next generations, if it’s inherited, as in the case of the Dutch famine.
