Genetic tests: those who say they see the risk of various diseases may be deceiving – 05/07/2022

The promise is this: to decipher everything that can reveal your DNA, everything. And look, he would be able to tell you a lot of things — with great ease, that’s what they’re saying around.

For a reasonably cheap price, maybe even in installments, you would receive the kit at home to do a genetic test. In it, you would find that kind of long cotton swab to stick in your mouth and rub the inner walls of your cheeks. Okay, just keep the material collected in the envelope that comes with it and return it to the laboratory.

In a few weeks, then, a report would come out showing its origins. Perhaps your ancestors came from distant and exotic places, have you ever thought?

But, according to your investment in this search for self-knowledge and in the desire to prevent diseases, you would gain more information. Do you have a genetic predisposition to like sweets or to suffer from a lack of one nutrient or another? Do you have a tendency to form wrinkles or ear wax? There you go. Seriously, I’m not kidding.

Or rather, it would be almost recreational if the results didn’t show the supposed increased risk for complicated diseases like diabetes, Alzheimer’s, heart attack and various types of cancer.

Then, unfortunately, depending on the test you make, you may panic for nothing, believing in some high risk that, in fact, never existed.

Or, worse, he will breathe a sigh of relief, assuming that the probability of having a particular tumor is small, so he confidently makes mistakes in the screening tests when, in reality, his risk has always been high.

This type of product offered to the general population falls into the same category as pregnancy tests and many others that you can do directly, without going to the doctor to get a prescription. In fact, that’s why health plans don’t cover it.

The point is that, when it comes to genetic tests direct to the consumer, in addition to many results being wrong — well, there is no legislation to regulate them and some are not validated to guarantee quality — there are possible pitfalls.

To know ancestry works

Your DNA is made up of over 3 billion pairs of letters or base pairs. Platforms for these tests look at just a few thousand of them, typically looking for what geneticists call SNP or single-nucleotide polymorphism. Ah, here’s the tip: they pronounce “sníps”

In other words, it’s as if these tests took a few points from your genetic material and checked if, right there, there wouldn’t be an SNP — that is, a single letter different from the one expected in the little pair.

“But these one-letter polymorphisms rarely cause any disease”, guarantees doctor Rodrigo Santa Cruz Guindalini, from Oncologia D’Or, in Salvador, Bahia.

In fact, if they provoked us, we wouldn’t even reach adolescence. Because we have countless SNPs—they that make one individual different from another.

According to Guindalini, who is an oncologist and oncogeneticist, science already knows well which SNPs are common in all people of Asian, African and so on. “So these tests are even able to pinpoint where someone’s ancestors came from. But they completely miss the point when they try to determine the risk of disease.”

First: there are crooks and crooks

In very rare cases, it is quite true, a single letter changed is enough to cause a huge mess. That’s when experts say there’s a high-penetrance genetic variant. The term means that it increases the risk of a certain disease appearing by more than five times.

“Imagine a malignant breast tumor. Every woman has a risk between 10% and 12% of having this disease throughout her life”, says Guindalini. “But if she has one of these high-penetrance variants of breast cancer, her risk of developing it is 50% or more.” Indeed, a huge threat.

Who doesn’t remember the BRCA1 genetic variant that led actress Angelina Jolie to remove her breasts and then her ovaries out of sheer precaution? Well, it’s a good example.

But many of these tests that are the trend of the time do not go after the genetic variants of high penetrance for the various tumors that appear in your report. Not even for the moderate variants, also rare, capable of multiplying the risk from 1.5 to five times. Therefore, the person can be happy with the result and have one of them. A cruel illusion.

And what do these tests see, then? “They see those SNPs that are quite common in the population, but that, in isolation, increase the risk of cancer by only a tiny 0.01% or 0.1%”, replies the doctor.

Some of these tests are impressive when, in the result, they use the colors of the traffic light and point with red the SNP that would represent a high risk. “But this information is useless”, reinforces Guindalini.

You need to look at the whole

This is the second point. Guindalini compares an SNP to a bandit who only acts in a gang. “When several seemingly innocent SNPs combine their strengths, the situation can become dangerous,” he says.

But I warn you: it’s no use adding up all the red, yellow and green dots of the report of such a genetic test to try to understand what genes say about your health. It doesn’t work like that.

“There are complex mathematical models to simulate the interaction of all these polymorphisms. After all, some favor cancer and others, on the contrary, are protective”, says Guindalini. “The result, fundamental to our work, is what we call the polygenic risk score”

If you have a low score of 1%, your chance of having a particular cancer is 2.5% over a lifetime. But if the score is 99%, very high, even without any variant capable of acting alone, like Angelina Jolie’s, your risk of having cancer goes up to 33%.

In England, says Guindalini, the polygenic score is already being applied to determine how often a woman would need to have a mammogram. “If the risk is low, she only repeats the exam every three years,” she says.

The oncologist finds it unlikely that these genetic tests offered directly to people use such mathematical models. “This is not written in the report”, he notes. “Not to mention that these tests talk about so many diseases at once that it’s hard to imagine that they apply the score to all of them.”

We are not even the parameter

One more: the SNPs that increase the risk of diseases tend to be different for each population.

“When the test looks for five letters scattered throughout the DNA to indicate whether an individual may have polyps in the intestine, it does so because these five letters have been associated with the problem in a specific population”, explains geneticist Diego Miguel, medical director of Igenomix Brasil , a multinational reference in genetics.

The accuracy of the test may have been checked, for example, on American Jews. And, in northeastern Brazilians, the polymorphisms behind the risk of polyps may be others, which would be overlooked.

The story of each

For Diego Miguel, it is essential that the laboratory cross-references the genetic risk score with calculators that consider clinical data: age, whether the person is overweight or obese, smokes, drinks, uses hormones, has had infections and much most.

“It’s the combination that gives us precious revelations”, he informs.

Genetic tests, then, wouldn’t work?

To predict the risk of disease, they work — only, safer, in another way. If that’s your concern, it’s best to see a doctor. And, of course, do the exam in the laboratory, in the correct way.

“We need to go after all the genes that have to do with the disease in focus”, says Miguel. “Only, instead of looking at bits and pieces of them, the right thing is to carry out a complete reading, from the first to the last of their lyrics”, he describes. So there is no way for something to escape.

The necessary follow-up

The geneticist doctor does not enter the scene only in the interpretation of the result. He must guide the patient before the test and even find out if he prefers not to know some information — which is a right.

According to him, it is advisable not to dig into the genetic risk of diseases when, at least for the moment, this knowledge will not help anything in prevention or treatment. It’s the case of Alzheimer’s.

If these tests sold directly to any of us can be wildly inaccurate, giving a false sense of security or pointless scares, why are they offered? For Diogo Miguel, deep down what they are looking for is something that is worth gold: information.

“A pharmaceutical company might pay dearly to find out what proportion of people in a population would have a polymorphism that would increase the likelihood of adverse effects from one of their drugs,” he speculates.

The fact is that people are attracted. There is a test promising to see, in addition to diseases, genetic compatibility with the loved one. Instead of a test, I would prefer flowers.

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