Genetic epidemiology of hereditary tyrosinemia in Quebec and in Saguenay-Lac-St-Jean.

Hereditary tyrosinemia type I is an autosomal recessive disorder that was recognized in Saguenay-Lac-St-Jean (SLSJ) (Quebec) in 1967. Ninety-eight tyrosinemic children, including some of the 113 children born in the SLSJ region, have been screened by the Quebec Network of Genetic Medicine in the whole province since 1970. The geographical distribution of the 98 children screened showed the majority of them to have been born in the northeastern part of Quebec. The prevalence at birth was estimated at 1/1,846 live borns, and the carrier rate was estimated at 1/20 inhabitants in the SLSJ region. Three control groups matched to the tyrosinemic obligate-carrier couples were generated using the population register of the SLSJ region kept at SOREP. The mean coefficient of inbreeding was only slightly elevated in the tyrosinemic group compared with the control groups and was due to remote consanguinity. The mean kinship coefficient was 2.3 times higher in the tyrosinemic group than in the control groups. In the SLSJ region the places of origin of the tyrosinemic children and their parents did not show a clustered nonuniform distribution. Endogamy was not found to be higher in the tyrosinemic group than in the control groups. All these results support both the hypothesis of a founder effect for tyrosinemia and a high gene frequency in northeastern Quebec.