Genetic testing: when it is indicated and what care you should have, according to doctors

Imagine you taking some blood or saliva and finding out where your ancestors came from, what type of physical exercise is right for your body, the most appropriate food for your health and the risk of developing thousands of diseases.

This is the promise of the companies that offer genetic tests, a market that is booming in Brazil and in the world and which offers increasingly competitive prices.

The greater availability of these tools is related to a huge technological evolution. To give you an idea, the Human Genome Project, completed in 2003, took 13 years to complete, cost about US$ 3 billion and required the use of 240,000 genetic sequencers, spread across 20 research centers in various parts of the world. A little less than two decades later, today it is possible to carry out DNA analysis for something around R$1,000 to R$3,000, in 24 hours and with just one machine.

And the advances are not limited to cost, equipment and time spent: the understanding of different genetic sequences and what they can mean in practice has evolved a lot in these 20 years.

But do all these tests really work and can they bring some relevant information? In what cases are they really indicated?

According to geneticists interviewed by BBC News Brazil, some of these options really make a difference. Others, however, still do not bring reliable and scientifically validated information, as you can see below.

ancestry tests

One of the most popular and affordable options on the market, they have the basic premise of telling you where your ancestors came from.

In practice, this test compares parts of your DNA with a huge database and tries to find genetic traits in common with some typical groups in specific regions of the planet.

Thus, the result reveals with a certain degree of confidence its ancestry – saying, for example, that its genetic material comes 20% from Central Africa, 15% from Sub-Saharan Africa, 10% from the Iberian Peninsula and so on.

While the quality of these types of exams has improved in recent years, it is important to remember that they are not 100% accurate. There may be some distortions in the results, especially if your family comes from a region with little genetic information in the database used to make the comparison.

“Unfortunately, most of the genomic data are generated in developed countries in North America and Europe”, laments physician Roberto Giugliani, head professor of genetics at the Federal University of Rio Grande do Sul (UFRGS).

“This is something we still need to advance: expanding the availability of genetic sequencing from other parts of the world,” adds the specialist, who is also co-founder of Casa dos Raros, a training and education center on rare diseases.

Experts therefore suggest that genetic tests for ancestry be interpreted as something informative, recreational and a way of seeking self-knowledge. But the results should not be taken to iron and fire.

Diet, exercise and skin

Still in the field of recreational tests, it is common to see laboratories offering tests that, supposedly, would help to indicate the most appropriate diet or type of physical activity according to your genes.

Some go further and provide an analysis of the patient’s skin, indicating possible predispositions to diseases and indications for dermatological treatments.

In this context, doctors urge a lot of caution: we still don’t know our genome well enough to reach this kind of broad conclusion.

“Often, these tests take into account a small study that was carried out in the population of Yemen, in which researchers observed a greater propensity to like broccoli in individuals with certain genetic characteristics”, hypothesizes the doctor Maria Isabel Achatz, coordinator of the Unit of Oncogenetics at Hospital Sírio-Libanês, in São Paulo.

Although investigations of this type are valid, it is not appropriate to extrapolate the results as if they were absolute truths for literally everyone.

“Some companies build huge panels with information of this type, and it is often impossible to check the source of all the conclusions that appear in these reports”, continues the geneticist.

For now, the recommendation is not to take this genetic test option on food or physical activity as something serious and as a basis for changing habits, behaviors and lifestyle.

Even because basic health guidelines are relatively the same for everyone: it is important to have a varied and balanced diet, rich in fruits and vegetables and low in ultra-processed foods, and to do at least 30 minutes of moderate or intense physical activity every day. days.

most common diseases

The discussion about the need to carry out genetic tests extends to yet another field of human health: is it worth undergoing such a test to discover the risk of developing the most frequent diseases, such as high blood pressure, diabetes or Alzheimer’s?

Most of the time, the experts’ answer to this question will be a loud and resounding “no.”

The physician Mayana Zatz, a professor of genetics at the University of São Paulo (USP), teaches that these diseases usually have a complex genetic inheritance and are related to several characteristics of the DNA.

“In other words: we are talking about conditions related to several genes and for which there is a very strong influence of environmental factors and the behavior of the individual”, adds Zatz, who also coordinates the Center for Studies in Human Genome and Stem Cells at USP .

In practical terms, such an exam can even estimate, with a high degree of uncertainty, a greater genetic propensity for high blood pressure, for example. But the problem tends not to appear (or to be milder) if the person does physical activity, does not smoke and has a balanced diet.

“And let’s suppose that I do a type test and it appears that I have an increased risk of diabetes. What will the doctor’s recommendation be? Eat healthy, do physical activity, not gain weight… for everyone”, argues the geneticist.

Achatz recalls the story of a patient who arrived at her office saying that he had discovered, through a genetic test, that he had a 30% risk of Alzheimer’s in the future.

“The person sat in front of me with swollen eyes from crying so much. She told me that, when she received the news, she wanted to die”, says the doctor.

“My recommendation was clear: take the report, tear it up and throw it in the trash.”

One of the major problems in these cases, point out the experts heard by BBC News Brazil, is that the results on the propensity to develop one disease or another are provided by the internet, in an impersonal way and without any kind of guidance.

Genetic counseling, carried out by someone who specializes in the subject, is essential for interpreting that sea of ​​information and putting into perspective what the test found written in the DNA.

“Often, the individual sees that 30% risk of Alzheimer’s and doesn’t even remember the other 70% chance of not developing the disease”, completes Achatz.

Cancer

It is no exaggeration to say that oncology is the area of ​​medicine that has benefited most from genetics so far.

“The tests help, for example, to identify who has a genetic profile that predisposes to certain types of cancer”, cites Giugliani.

“With this, the monitoring of the disease is much more personalized and helps to identify cases early on, when there are more chances of successful treatment”, says the doctor. In some situations, it is even possible to act even before the cancer cells appear.

The most famous example here is that of Angelina Jolie. In 2013, the American actress announced that she had undergone preventive surgery to remove her breasts, after discovering that she carried mutations in the BRCA 1 and 2 genes, which are directly related to tumors in this part of the body.

Let it be clear: a test of this type is not indicated for all women and must necessarily undergo a medical evaluation. Jolie herself only did it because she had a family history of breast cancer, one of the factors that suggests the need to scour DNA for this kind of information. The recommendation therefore varies from case to case.

And look at that advances in genetics are not limited to the early detection of cancer. Today, these exams help to monitor the whole family and make it possible to determine the best treatment for each patient.

“After the diagnosis of the disease, the result of a genetic analysis, when there is an indication to do it, has the potential to modify the therapeutic strategy that will be adopted”, reinforces Achatz.

Let’s suppose that doctors find an X mutation in a patient with lung cancer. Currently, there are specific remedies that only work when this change is present in the genome. In a second case, which presents the Y mutation, another drug will be more suitable.

monogenic diseases

Finally, we cannot forget about diseases classified as monogenic or Mendelian.

“They are caused by mutations in a single gene, which makes a person develop that condition”, teaches Zatz.

An estimated 6,000 diseases fit this description, such as sickle cell anemia, cystic fibrosis and Duchenne muscular dystrophy.

And even in these cases, in which the tests are very reliable and close the diagnosis of a disease, the indication for doing them is restricted.

“Usually, we only recommend carrying out tests of the type when the person knows that there is a history of these diseases in the family”, suggests Zatz.

In such cases, a DNA analysis would be quite beneficial. A couple who are thinking about conceiving a child and have a history of single-gene diseases in close relatives, for example, can be tested for certain mutations, which are likely to be passed on to future generations.

If these mutations are actually detected, the couple can opt for artificial insemination and genetic analysis of the embryos.

Thus, only those embryos that do not have the mutations will be implanted in the woman’s uterus. This completely rules out the risk that the future baby will have the particular single-gene disease that is relatively common in that family.

“This type of test is still quite expensive, but we need to consider the health, emotional and financial impact that such a disease has on a child’s life and everyone around them”, analyzes Zatz.

“To give you an idea, there is a group of diseases called Spinal Muscular Atrophy, or SMA. Today, treating this condition alone costs US$ 2 million. Can you imagine preventing the birth of a child with this condition?”, asks the geneticist.

This, by the way, leads us to another discussion: is it worth knowing that you have a serious illness, for which there is still no therapy?

“Often, the diagnosis ends the search for an explanation for the symptoms that the person has had for years. As difficult as it is to receive such news, knowing about the disease can help the individual to turn the page and move on”, he says. Giugliani.

“And we need to remember that there is always something that can be done. Medicine does not treat the disease, but the patient”, adds the doctor.

But what about when the subject still does not have a serious disease and no drugs are available, but carries the mutations that will lead to the development of the condition later on, from 50 or 60 years of age?

“The consensus is not to test children for diseases that will only appear in adulthood and for which there is no treatment”, thinks Zatz.

“When this test is done in childhood, we take away the individual’s right to decide whether or not he wants to know about it when he is an adult”, he says.

The geneticist believes that, most of the time, people prefer not to know that information, which can be a source of constant distress.

“The other day I was teaching at the USP School of Medicine and I asked how many of the young students would like to know if they had an increased genetic risk of developing a debilitating condition at the end of life. Half of the class raised their hands”, he says.

“Following, I said that all those who agreed were invited to come to my laboratory to do this test.”

“Until now, none of them have appeared there”, concludes the geneticist.