The intense mismatch between people of indigenous, European, and African origins that characterizes the Brazilian population has helped scientists identify a variant of DNA that is associated with a higher risk of obesity in women. It is a variation of African descent that is more common in adults who carry a higher proportion of genetic inheritance from Africa.
Although it is only present in 1% of the study participants, the DNA variant is twice as common in obese women and almost ten times more common in patients with morbid obesity.
It may seem like little, but it’s one of the most noticeable genetic effects ever seen in obesity. This is a complex and multifactorial trait – that is, it arises from multiple influences, including hundreds of different genes, as well as foods. physical activity and stress, for example. In addition, there are still few studies worldwide to collect this data in non-European and mixed population groups (only 5% of the people included in such studies are not Europeans).
The study has just been coordinated by researchers from the UFMG (Federal University of Minas Gerais) and published in the International Journal of Obesity with the participation of teams from Peru, the USA, Australia and African countries. The work is part of the Epigen-Brasil project, a broader effort to map the interaction between the DNA diversity of the Brazilian population, especially their mixed nature, and factors influencing the occurrence of complex diseases.
“We decided to conduct the obesity through misgeneration mapping study in 2016 on the basis of existing data from the Epigen-Brasil project,” says Professor Eduardo Tarazona-Santos from the Department of Genetics, Ecology and Evolution at the UFMG.
Finding genetic variants that are significantly related to complex health problems is, in a sense, like looking for a needle in a haystack. In general, researchers rely on large sample populations – tens of thousands or hundreds of thousands of people – whose DNA is compared in search of associations between different forms with the disease we want to study (e.g., the occurrence of a particular type of cancer) in whom it carries a certain “letter” substitution in the DNA on chromosome 10).
Conducting this search in misgenerated populations can be less of a hassle, as their chromosomes are already divided into a mosaic of DNA “blocks” inherited from their various ancestors (see infographic), explains lead author of the study, Marília de Oliveira Scliar . “First of all, it is possible to establish the association between these blocks and the characteristic of interest. Then we do a fine mapping to identify the specific region within them. “
For this purpose, the team initially deployed three groups of volunteers, whose health status is being examined over the long term in Brazil. There are 3,653 residents of Pelotas (RS), all born in 1982; 1,442 elderly people from Bambuí (MG); and 1,246 residents of Salvador, followed by 1997 when they were children. To measure the incidence of obesity, the researchers had data on BMI (body mass index, which is the weight of the person divided by the squared height).
From this database and ancestry information, the team eventually found a variant of just one “letter” of DNA in the Pelotas population that has a significant association with obesity. It was found in 31 women who were unrelated and whose BMI was above the group average (28 versus 23).
Their DNA also made up 35% of Africa, versus 16% of the average for the gaucho group, but some of them declare themselves white, showing that Brazilians’ ancestry is much more complex than their physical appearance or self-esteem Show perception.
The link between DNA letters and obesity was also found in older women in São Paulo, who participated in another genomic study, and in Bambuí, but not in Salvador. Outside of Brazil, the effect of the variant was also observed in women from Soweto, South Africa. In addition, the researchers found that although the variation is very rare in Europeans, it occurs in 3% of West African residents in places like Nigeria known to have been affected by the slave trade with Brazil.
It is unclear how exactly the variant affects the organism. It is possible that it is a regulatory region of DNA. In other words, it does not contain the recipe for the production of a molecule in the organism, as does the genes themselves, but it could affect the activation or deactivation of one or more genes. One of the group’s hypotheses, due to the variant’s association with obesity in adult women, is that it is associated with the accumulation of fat reserves for pregnancy and lactation – something that, when combined with modern day calorie diets and physical inactivity, would facilitate the onset of obesity.
For the doctor Bernardo Horta, professor at the Federal University of Pelotas and co-author of the study, the work shows a research path that still needs to be intensified in Brazil. “We need more data from population-based studies that have been collected over a lifetime. Only then can we visualize the associations and interactions between genes and the environment more clearly, ”he says. We are a family company.