Myotonic Dystrophy Steinert disease








Myotonic Dystrophy, Also called Steinert's disease in honor of the Doctor who described this disease in 1909, is the most frequent form of muscular dystrophy in adults. It is observed within all populations and touches all races. The prevalence (number of individuals suffering from the disease vs. total population number) is estimated at 1 per 10 000 inhabitants in most countries. Steinert Disease is 20 times more frequent in the Charlevoix/Saguenay-Lac-Saint-Jean region than in any other country in the world. In this region, it is estimated that 1 in 500 people is affected by this disease. Genealogical studies of families affected by Myotonic Dystrophy and living in the Saguenay region have enabled the identification of a couple common to these families. This couple, Noël Simard and Marie Madeleine Racine, both of French origins, were married in 1661 in Château Richer and had 14 children (eight boys and six girls) who in turn also all married. Three of their children established themselves on Côte-de-Beaupré and the 11 others in Charlevoix, from which some of their descendants moved to the Saguenay region. It is probable that one of the two ancestors was a carrier for the Steinert's Disease gene, although this remains to be proven. This study has demonstrated that all the cases of Myotonic Dystrophy in the Saguenay region probably stem from this ancestral couple. How can we explain the very large number of individuals affected by this disease from a single ancestral couple? There were two contributing factors to the proliferation of the disease. The first factor is a particularly high fertility level. The population of Saguenay totalled a few hundred inhabitants in 1840. This number rose to 6,027 in 1851, to 37,367 in 1901 and to more than 280,000 during the 1980s. A second factor is the low emigration rate that confined the disease to the same region. These two factors certainly explain the propagation of the disease in this region. On the other hand, inbreeding seems to have had very little effect on the development of Myotonic Dystrophy since this disease is dominant and you only need one spouse as a carrier for transmission of the disease. Whether spouses are related or not has no effect on the risk of transmitting or developing the disease.