La prévalence et la distribution des maladies génétiques au Québec : L’impact du passé sur le présent

Abstract

Après un bref résumé de l’histoire du peuplement du Québec, cet article décrit comment cette histoire exerce son influence sur la prévalence et la distribution des maladies génétiques au Québec. On aborde d’abord quelques concepts de base de génétique des populations (effet fondateur, dérive génétique, endogamie) et comment ces concepts s’appliquent à la population du Québec. On montre ensuite comment les conditions dans lesquelles le peuplement du Québec s’est effectué ont pu favoriser des modifications de la fréquence de certains allèles par rapport à leur fréquence dans la population française d’origine. Il en résulte que certaines maladies génétiques revêtent des particularités propres à la population québécoise. Finalement, on verra comment la connaissance de ces particularités peut être utile sur le plan clinique, car elle influencera à son tour le médecin dans son diagnostic différentiel, ainsi que dans la mise au point, l’utilisation et l’interprétation de tests diagnostiques.

The prevalence and distribution of genetic diseases in the province of Quebec has been influenced by its population history. The current French Canadian population stems from 8,500 pioneers who left France for Nouvelle-France between 1608 and 1759. After the English conquest of Nouvelle-France in 1759, the French Canadian population remained mostly genetically isolated, for linguistic, cultural, and religious reasons. The migration of a small number of French individuals to Nouvelle-France created a founder effect. Subsequent migrations inland have created smaller regional founder effects. The limited size of the population favoured genetic drift, and the social context encouraged endogamy, i.e. unions between French Canadians with little admixture with English and other immigrants. Founder effects, genetic drift, and endogamy have all played a role in the current prevalence and distribution of genetic diseases now found in Quebec. The prevalence and distribution of genetic diseases in Quebec need to be taken into account in clinical practice. When clinicians are knowledgeable about the genetic diseases prevalent in the population they treat, they know to consider these diseases in differential diagnoses when appropriate and prioritize investigations accordingly. When developing a new diagnostic test for a genetic disease, the prevalence of the disease and the nature of the mutations found in the target population need to be taken into account. The performance of the test will depend on how well it accounts for the particularities of the disease in that population. In other words, how well does it detect the mutations found in that population ? Interpretation of individual genetic test results will also depend on how well the test is expected to perform in the individual’s population.