With the current popularization of genetics, it is difficult to find someone who has never heard statements such as “the cradle of human diversity is in Africa” or “the Brazilian population is special because they are very mixed“.
These statements grew in relevance due to several initiatives of massive sequencing of populations around the world, enabling the emergence of a new profile of human diversity.
But what are the real implications of these statements? What do these particularities really mean for population studies? And besides, what do they mean directly to individuals?
Human population genome sequencing in the spotlight
The American Society of Human Genetics meeting, which took place in October this year, had a presentation about a complete genome sequencing initiative of African populations.
About four hundred representative individuals from 13 countries and over 50 ethnolinguistic populations displayed more than 3 million unique variants of these populations, meaning they are NOT present in European populations.
This study is part of an initiative for sequencing the genome of the African population and unveiling the diversity present in the cradle of humanity.
Another paper presented at the same meeting by the University of California demonstrated, with the sequencing of 220 individuals worldwide, that the sequence we have used as a reference for mapping all genomes in recent years has at least 7 million unrepresented bases. Roughly, this means that 7 million points in the genome have not been evaluated for their diversity.
But what does all of this mean? And why does it affect the Brazilian population in such a special way?
Every day we see increasingly more genetic tests available that claim to be able to predict health outcomes in any individual. These tests consist of direct-to-consumer tests (known as DTC tests) or even exams with a clinical focus requested by physicians.
Many of these tests are offered abroad and purchased by Brazilians hoping to find answers in genetics that leads them to a healthier and longer life. Unfortunately, there is no scientific evidence to support this supposed predictive power of genetics on these tests. Only in a minority of them science has shown effect.
Direct-to-consumer genetic testing (DTC)
Are they universal? Do they work on any individual?
I suppose the first thing that comes to mind is that as a homogeneous species – 99.9% of shared human similarity – wouldn’t it be enough to make universal genetics?
We still don’t have an answer for this question, and that is why the human diversity studies are important. That small number that sets us apart – 0.1% – may mean nothing, but it can also mean everything!
So how to know our true ancestry?
Today, most studies that use genetics to predict health and well-being outcomes are conducted in populations with European ancestry, which implies that models are tested on a certain set of variations that may not apply to other specific populations.
Without arguing about ethnicity questions, most human diversity is still within populations and not between them. This is fundamental to the reasoning that not all diversity can not be taken into account in specific population studies. This means that even a European population may not be represented by the studies.
And when we talk about Brazil, unless you know your entire family tree from 5 generations back, there is a huge chance that your genetic material is a mix of several other populations. This makes the variation produced unique in content, although not as new as the African scenario most likely is. These complex mixtures have no representativeness out of Brazil, and this is what needs to be studied in-depth and understood in detail, so that we can understand whether it is possible to transpose these studies and apply tests hoping that the results will be compatible.
Can we do proper genetic testing?
The answer today is unclear. We encourage further studies in this area to deepen the understanding of the genetic profile of Brazilians. The application and validation of these tests in this population is essential for Brazilians to achieve the same quality of medicine already present in more developed countries.
For now, before taking a genetic test, whatever it may be, you need to know if this test applies to you, individually and population-wise. Be a conscious agent of your health.
Ganguly, Prabarna. NHGRI funds centers for advancing the reference sequence of the human genome. National Human Genome Research Institute. September 24, 2019.
African Genome Variation Project. Wellcome Sanger Institute.
Sequencing African Genomes Yields New Data Resource with Broad Applicability. Findings Reported at ASHG 2019 Annual Meeting. October 15, 2019