Homozygous familial hypercholesterolemia among French Canadians in Québec Province.

Nineteen patients with homozygous familial hypercholesterolemia (FH) living at the time of the 1981 Canada census are the subject of this report. Their mean age at that time was 15, with a range of 1 to 26 years. All patients had extensive xanthomatosis but showed variable clinical manifestations of coronary heart disease (CHD); five (mean age, 21; range, 11 to 27 years) died from sudden death due to CHD. Plasma cholesterol levels varied more than twofold (557 to 1532 mg/dl). Variation in the concentrations of both plasma and low density lipoprotein cholesterol, as well as apolipoprotein B, were related neither to age at death from CHD nor to the clinical course of CHD. The mean high density lipoprotein cholesterol concentration (37 mg/dl) was lower than the mean value (49 mg/dl) in the control population (p less than 0.001). Both the clinical and biochemical features of this cohort are typical of homozygous FH. The prevalence of homozygotes among French Canadians in Québec was approximately 1:275,000, and the minimum estimated frequency of heterozygotes was 1:270. In northeastern Québec, the frequency of homozygotes was approximately 1:100,000, and the minimum estimated frequency of heterozygotes was 1:154. Only Afrikaaners in South Africa have correspondingly higher frequencies.