Genes and life expectancy
"The Riddle of the ageless jellyfish"
How Science Slows Down Aging
Modern medicine allows us to live longer than ever before. However, sooner or later our body still gets old and becomes more vulnerable to diseases. It is hardly possible to invent an anti-aging pill, but fortunately, science is quite capable of slowing down this process. In the book "The Riddle of the Ageless Jellyfish. Secrets of nature and achievements of science that will help us get closer to eternal life" (Mann, Ivanov and Ferber publishing house), translated into Russian by Alyona Yuchenkova, molecular biologist Niklas Brandborg tells what scientific discoveries can allow our body to stay young and healthy. We invite you to familiarize yourself with the fragment, which explains why scientists believe that genes do not play a significant role in life expectancy.
Why the importance of genes should not be exaggerated
We humans are strikingly different from each other. Someone is an introvert, and someone talks incessantly. Someone is fast, and someone is not very fast. Someone has blue eyes, someone has green, and someone has brown.
Scientists believe that some of these signs are determined by heredity, and some by the environment, the environment in which a person grew up.
Some signs are 100 percent innate, they are embedded in our genes, and some are acquired, formed by life experience. For example, education will not affect the color of a person's eyes in any way, but it is in the process of education that the native language is learned.
However, this division is a bit artificial: many signs are both hereditary and acquired. For example, a person's personality: certain inclinations are inherent in nature (for example, a bright temperament), but it depends on the upbringing and the environment in which a person grew up, where these inclinations will lead — for the better or for the worse.
There are several ways to determine to what extent the environment and genes affect a person.
This means that it is possible to determine what exactly is caused by this or that trait — genes (eye color, for example), environment (native language) or both (human personality).
One of the most popular methods is the study of twins. We use the gift of nature. Identical twins have the same DNA. Genetically, they are clones: identical twins come from the same sperm that fertilized one egg. Exactly as it happens in a normal situation. After fertilization, a cell containing the genetic material of both parents (zygote) begins to divide, two cells are obtained, then four, and so on. Sometimes the first two blastomeres are not held together, they separate from each other and a separate person develops from each of them, as is normal from a zygote. In this case, two embryos have absolutely identical DNA, but two different people grow out of them. Such people are called identical twins, since they came from the same egg.
Fraternal twins, on the contrary, have different DNA: they are obtained from two eggs, each of which is fertilized by its own sperm. This means that fraternal twins are genetically related to each other in the same way as ordinary brothers and sisters.
This difference between identical and fraternal twins is used to determine what effect genes have on a particular feature of a person. Both pairs of twins grow up in the same environment — they have the same house, the same parents, they are the same age, and so on. But the degree of genetic similarity between them is different: the identical ones have the same DNA, and the fraternal ones have only a part of it. If genetic clones — identical twins — are more similar to each other in some way than fraternal twins, then this trait depends more on genes.
In one of the most famous studies of the life expectancy of twins, children born between 1870 and 1900 were observed.
The study showed the so-called heritability of life expectancy at the level of 0.26 for men and 0.23 for women. Other studies have confirmed these results: 0.25 among Amish, 0.15 in Utah and 0.33 in Sweden. The exact figure doesn't really matter. It is important that the heritability index is quite low.
Heritability is a kind of technical concept that makes sense for individual traits that can be measured. The meaning of this term can be explained as follows: indicator 1 means that all the differences on this trait between individuals are genetically laid down. Thus, if the heritability, for example, of a person's height was 1, it would mean that the difference in the height of adults is explained solely by the difference in their genes. With heritability 0, all differences are explained solely by the difference in the environment and do not depend at all on genes.
Thus, the indicator of the heritability of life expectancy at the level of 0.15–0.33 may mean that life expectancy is mainly determined not by genes.
* * *
The famous University of Minnesota study studied twins (both identical and fraternal) separated at birth and raised in different families. It is striking that identical twins developed very similarly, although they grew up in different places and were not familiar with each other.
The author of the study Nancy Segal talked about a pair of twins James Lewis and Jim Springer (There is evidence that both brothers were called the same — Jim). The brothers first met when they were about forty years old. Until then, their lives were very similar: they regularly went on vacation to the same place in Florida, both bit their nails, owned light blue Chevys, suffered from headaches equally and worked part-time at the sheriff's office and at McDonald's. One of the twins named his son James Alan, and the other — James Allan. The first wives of both twins were named Linda, later both divorced and married a second time to women named Betty.
Of course, the name of the wife is not in our genes, but the life of these brothers proves to us how important heredity is.
Similar studies of twins are conducted all the time, but scientists have developed other clever methods for studying the contribution of genes to ensuring the diversity of people.
Huge databases hosted on the Internet are very often used. Take, for example, the company Calico (California Life Company), owned by Google. Together with the site Ancestry.com helping to find relatives based on a DNA test, the company has formed more than 100 million family trees. Based on the information provided by users, scientists receive a huge amount of data on life expectancy in different families. And, of course, they can be analyzed.
A large study conducted by Calico and Ancestry.com , primarily confirmed the heritability indicators established by previous studies. Genes have a significant effect on many human traits, but obviously not on life expectancy.
During the study, an amazing fact was discovered: in spouses who are not, as a rule, genetically related, life expectancy coincides more often than in children of the same parents of different sexes. This means that life expectancy depends not only on the genetic factors inherited from your parents, but also on who you live your life with.
We choose people similar to us as our spouses. Of course, it is impossible to know in advance how long a spouse will live. And yet two people have been living in the same house for many years, raising the same number of children at the same time, often eating the same, resting together and generally having the same or similar living conditions. It may also have some significance that stable couples are formed by people who have a lot in common, and these common features affect life expectancy (for example, education level, income, attitude to alcohol or sports).
I deviated from the topic of conversation to show that we want to believe that life expectancy is genetically determined, but in fact it is not so. When scientists remove the moment of choosing people similar to us from the study, heritability decreases to the level of 0.1. Thus, almost nothing depends on genes. And this is very good news, because it means that we ourselves can influence how long we live.
Life expectancy and genes
When studying the effect of genes on life expectancy, the problem of long waiting arises. The research participants were born at a completely different time than you or me. And this could significantly affect the result.
The same can be said about growth: once the environment influenced the growth of an adult much more than it does now. If a person was born into a wealthy family, he received enough calories, ate a lot of meat, ate a variety of foods, and so on. At the same time, in many poor families, children periodically starved, ate the same way and often got sick. Today we all live better than the richest people of the last century, so people more often reach the upper limit of growth possible for them genetically.
Probably the same thing will happen with life expectancy: the more people have access to optimal conditions for a long life, the more important the genetic predisposition will become.
There are other signs that our life expectancy depends on us. One of the best examples is the relationship between a person's personality and life expectancy.
Personality researchers are convinced that one of the most important signs that determine a person's life expectancy is what is called conscientiousness in English. You can translate this concept of "organization" or "responsibility" — how organized a person is, how well he knows how to plan his time, how much he controls himself. It is not surprising that these things determine life expectancy: the better a person's self-control is developed, the better he organizes his life, the higher the probability that he adheres to a healthy lifestyle. Organized people are more likely to exercise, eat healthy food, smoke less, use all kinds of substances less often, and so on. The relationship between life expectancy and low anxiety is very interesting.
It is very useful to be a little anxious if this anxiety is directed at your well-being and helps to keep yourself in shape.
* * *
Genes do not play a big role in life expectancy, but their importance cannot be completely excluded. This means that, after all, genetics has something to teach us: if we reveal the genetic secret of longevity, we may be able to repeat it.
Genes are not magic and not fate. It's just the composition and amount of proteins in our cells. A genetic mutation (a change in the sequence of amino acids of a protein encoded by DNA nucleotides) leads to the fact that the protein changes its shape (and this may start working a little differently) or cells of an organ produce too much or too little of this protein at a certain period of life. No more than that.
Once we figure out what the genetic basis of longevity is, nothing will stop us from making a medicine with a similar effect.
Let's say we found out that a small change in the fictional Gen1 gene leads to a decrease in the production of the Gen-1 protein by this gene.
At the same time, we learn that such a variation of the gene increases the likelihood of living more than 100 years. So: lowering the level of the Gen-1 protein increases life expectancy. Now we can only repeat the same effect in artificial conditions. To do this, you can use medications that destroy the Gen-1 protein in cells (or in the intercellular substance) or slow down its production.
Once upon a time, scientists hoped to find out which of the millions of small genetic differences between people lead to the emergence of various phenotypic traits. But as a result of the progress of so—called gene sequencing — reading human genes - it is now possible to create what is called genome-wide association search (GWAS). It is these hard-to-hear calculations that underlie research.
The concept itself is not difficult to understand: in these studies, a lot of human DNA sequences are studied and the relationship between phenotypic traits and differences in nucleotide sequences in DNA is clarified. For example, if there is a variant of a gene that is always present in blue-eyed Danes, but absent in brown-eyed ones, this variant may be responsible for the blue eye color. If we already know by this point whether the protein produced by this gene is involved in the production of pigment or in its distribution in the iris of the eye, we will become even smarter.
In reality, everything is not so simple. Scientists have found out that the vast majority of our traits are determined by more than one gene or even a couple of genes. And thousands. For example, a person's height is statistically associated with variants of thousands of genes and all people have genetic mutations associated with higher or lower growth. To say something specific about a person, you need to calculate the overall effect. Scientists use some statistical tools for this, and the result of these calculations is called a polygenic risk assessment.
A simple example. Let's say we are a group of not too experienced scientists who want to find out which genes are responsible for anxiety. We compile GWAS for a large number of people and find out that the differences in anxiety levels are explained by thousands of different gene variants.
Now let's look at me and you. We use a very simple model: if a genetic variant increases anxiety, we will call it +1, otherwise -1. Adding up thousands of options, I get a risk level of +600, that is, I have a high risk of feeling anxious. You get 0. So I should probably write this book as soon as possible. And you can lie down on the sofa and read it.
Let's get back to the real researchers. To those who have developed an assessment of polygenic risk for life expectancy and made a very important discovery in this regard.
Placing the observed on a scale from the highest to the lowest indicator, scientists found that between ten percent of people at the top of the scale and ten percent at the bottom of the scale, the difference in life expectancy is five years. This means that by deciphering a person's genes, scientists were able to predict how long he will live on average.
This is just amazing, because, as we found out, genes do not play a big role in life expectancy.
Portal "Eternal youth" http://vechnayamolodost.ru