Rare diseases: the founder effect in Quebec better understood
There are actually several founder effects in the province, explains the lead author of the study, researcher Simon Gravel, from McGill University.
Saguenay–Lac-Saint-Jean has one of the most well-known grounding effects in Quebec. By combining genealogical data of unparalleled richness (attributable in particular to the files of the Catholic Church) with the genetic databases CARTaGENE and Genizon, Mr. Gravel and his colleagues concluded that the region was mainly populated by settlers who arrived from the Charlevoix region.
These settlers themselves had moved from Quebec to Baie-Saint-Paul to exploit the rich arable land created by an asteroid impact millions of years ago. When demographic pressure became unsustainable in the Charlevoix region, settlers left for Saguenay and then for Lac-Saint-Jean.
” The people who arrived in Quebec mixed relatively well. But then there are a relatively small number of individuals who have gone on to establish communities in each of the regions of the province. »
This is what happened in Beauce, a region inhabited by people who followed the course of the Chaudière River.
Furthermore, the researchers write, the genetic and pedigree data support the hypothesis that geography, and especially rivers and mountains, played a major role in establishing the main axes of migration and genetic variation.
Abitibi-Témiscamingue, on the other hand, was developed by people from all over the province, diversifying the genetic pool.
We therefore observe a lower founder effectexplains Mr. Grus.
In general, population geneticists have abstract theoretical models, says the researcher. It’s never happened in the past that we can make a model, that we can see it, that we have genealogy, that we can trace every line… Basically, we’re able to have this species with higher resolution population genetic mapping than has been done to date.
Most Quebecers trace their ancestry back to 8,500 settlers who immigrated from France in the 17th and 18th centuries. Previous studies, conducted notably by Professor Gérard Bouchard, revealed that the first 2,600 French settlers had contributed two-thirds to the Franco-Quebec gene pool.
Mr. Gravel and his colleagues therefore wanted to know if there had been a founder effect
imported by a few French settlers or whether it had arisen as the population grew and moved. The second hypothesis turned out to be correct, which in particular explains why we find founder effects almost everywhere in Quebec.
Approximately 500,000 Quebecers are affected by a rare disease. To cite just one example, let’s talk about familial chylomicronemia syndrome, which affects approximately one in a million people worldwide, but is slightly more common in the Saguenay and Charlevoix regions. Those who suffer from this condition are unable to break down the fats circulating in their blood.
Uniquely rich data
Quebec was possibly 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 are also making people jealous elsewhere on the planet.
When I spoke about it at a conference, I was asked if I would have to sell a kidney to access data like this, it’s so unique and incrediblesays the Quebec scientist, laughing.
This study, the conclusions of which are published in the journal Science (New window) (in English), could one day make it possible to identify the genetic mutations responsible for certain rare diseases.
” By better understanding how people are related, we could realize that the patients share the same genetic mutation and that it is therefore likely to be the cause. Clinicians could then work on a treatment. »
This study could also facilitate screening. If we want to better measure the prevalence of a rare disease in Quebec, we will use
this kind of mathematical model to say, well, according to the history of the transmission of this mutation, we would expect to find some in Saguenay, Charlevoix and Beauce, for exampleconcludes Mr. Grus.