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There are marked interethnic differences in β 1-adrenoceptor-mediated responsiveness, with sensitivity decreased in African-Americans and increased in Chinese compared with Caucasians. Therefore, the frequency of a common naturally occurring polymorphism of the human β 1-adrenoceptor gene (Arg 389 Gly), which has functional importance in vitro, was determined in 194 African-Americans, 316 Caucasian-Americans, 221 Hispanic-Americans and 142 Chinese. African-Americans were found to have a significantly lower frequency of the Arg 389 allele than the other three ethnic groups (all P< 0.01). In the populations studied, the order of the distribution of the Arg 389 allele was: Chinese (74%)> Caucasians (72%)> Hispanics (67%)> African-Americans (58%). To determine the functional significance of the Arg 389 Gly β 1-adrenoceptor polymorphism, in-vivo heart rate responses to exercise were compared …