The founding effect found in certain regions of Quebec, which could cause their residents to suffer from rare genetic diseases, for example, stems from the fact that they were founded by already related populations, a new study conducted by Quebec researchers shows.
Posted at 2:18pm.
Jean-Benoit Legault The Canadian Press
In fact, there are multiple founding effects across the province, explained the study’s lead author, McGill University researcher Simon Gravel.
For example, in Saguenay–Lac-Saint-Jean we find one of the most well-known founding effects in Quebec. By combining genealogical data of unprecedented wealth (attributed in particular to the files of the Catholic Church) with the CARTaGENE and Genizon genetic databases, Mr. Gravel and his colleagues determined that the region was populated primarily by settlers who came from the Charlevoix region .
These settlers moved from Quebec to Baie-Saint-Paul to exploit the fertile farmland created by an asteroid impact millions of years ago. When demographic pressures in the Charlevoix region became unsustainable, settlers moved to Saguenay and then to Lac-Saint-Jean.
“People who arrived in Quebec got along relatively well,” said Simon Gravel. But then there is a relatively small number of individuals who went on to create each of Quebec’s regions. »
This happened in Beauce, a region settled by people following the course of the Chaudière river.
In addition, the researchers write, the genetic and pedigree data support the hypothesis that geography, and particularly rivers and mountains, played an important role in determining the major axes of migration and genetic variation.
Abitibi-Témiscamingue, on the other hand, was developed by people from across the province, which diversified the genetic pool. We therefore observe a lower founder effect, explained Mr. Gravel.
“In general, population geneticists have abstract theoretical models,” Gravel said. It’s never happened in the past that you could make a pattern, you could see it, you had a genealogy, you could trace every lineage… Basically, we’re able to do higher resolution population genetic mapping for this species, than ever before ( Before). »
The ancestry of most Quebecers dates back to 8,500 settlers who immigrated from France in the 17th and 18th centuries. Previous studies, notably conducted by Professor Gérard Bouchard, had found that the first 2,600 French settlers contributed two-thirds of the Franco-Quebecan gene pool.
Mr. Gravel and his colleagues therefore wanted to know whether the founder effect had been “imported” from some French settlers, or whether it had occurred as the population grew and moved. It is the second hypothesis that turned out to be correct, which particularly explains why we see some founding effects across Quebec.
About 500,000 Quebecers are affected by a rare disease. To cite just one example, familial chylomicronemia syndrome affects approximately one in a million people worldwide, but is slightly more common in the Saguenay and Charlevoix regions. Patients with this condition are unable to break down the fats circulating in their blood.
Quebec may have been the best place in the world to conduct such a study because of the wealth of genealogical and genetic data available to researchers. The model developed by Mr. Gravel and his colleagues also makes people around the world jealous.
“When I was speaking about this at a conference, I was asked if I would have to sell a kidney to have access to such data. They are so unique and incredible,” said the Quebec researcher, laughing.
This study, the conclusions of which have been published in the prestigious journal Science, could one day make it possible to identify the genetic mutations responsible for certain rare diseases.
With a better understanding of the relationship between people, Mr. Gravel explained, we could see that patients share the same genetic mutation, and that this is therefore likely to be the culprit. Doctors can then work on a treatment.
This study could also facilitate screening. If we wanted to better measure the prevalence of a rare disease in Quebec, we could “use this kind of mathematical model to say that according to the history of transmission of this mutation, we would expect e.g. B. Saguenay, Charlevoix, and Beauce.” example,” concluded Mr. Gravel.