In 1992. 1812 individuals (1.2% of the population) were labelled at risk for malignant hyperthermia (MH) in seven families from Abitibi-Témiscamingue. To evaluate the effective risk in this population, a multidisciplinary study was undertaken which included clinical, genealogical and molecular aspects. This paper presents the clinical aspects of the study.

Purpose: In 1992, 1812 individuals (I.2% of population) were labelled at risk for malignant hyperthermia (MH) ~n seven families from Abitibi-Temiscamingue, To evaluate effective risk in this population, a multidisciplinary study was undertaken which included clinical, genealogical and molecular aspects. This paper presents clinical aspects of study. Method: For each of 1546 individuals reached, all anaesthetic exposures were screened for elements relevant to MH. Malignant hyperthermia events were analyzed with the clinical grading scale. All 44 reports of caffeine halothane contracture tests were reappraised, Finally, a genealogical study was done to complete each family tree up to initial French settlers in order to identify links between these seven families through common ancestors. Results: Following this reassessment, families were compared and classified into four groups. Two families (1097 individuals) are not considered to be at a higher risk for MH than population in general. Two families are styli considered possibly at risk. finally, one family (402 individuals) is highly at risk and two other families are probably at nsk. Family trees did not show any link up to colonization of Abitibi-Temiscamingue in beginning of this Century but common ancestors were found around 9 th generation, Conclusion: Th~s chnical reassessment will help to focus education and prevention on a much smaller group of tndividuals still considered potentially at risk for MH, By adequate evaluation of phenotypes, combined with use of a genealogical approach, it will be possible to target families for molecular research.