Paraoxonase phenotype distribution in Canadian Indian and Inuit populations.

Test objects were the sera of 57 North American Indian and 67 Inuit subjects. The paraoxon-hydrolyzing activity, a, was determined, as well as the paraoxonase-phenotyping ratio, c/b, a ratio designating enzyme activation by Na+ in the presence of Ca2+. The values of c/b were clearly bimodally distributed. Location of the modes and of the antimodal gap were in perfect agreement with the results previously obtained on Caucasian sera. This allowed us to retain the criterion which had been already established in the study of Caucasians, i.e., c/b less than 1.5 = "low-activity" phenotype, and c/b greater than 1.5 = "high-activity" phenotype. The proportions of individuals in each mode differed, however. In Caucasians, the frequency of the "low-activity" phenotype had been estimated as 51.2%. In Indians and Inuits, it was 7.0% and 6.0%, respectively. Independent of phenotype, Indian and Inuit sera displayed lower paraoxon-hydrolyzing activity than did Caucasian sera.