High frequencies and grade expressions of Carabelli's trait in a sample of the Croatian population

Although it is generally accepted that Europeans exhibit the highest frequencies of Carabelli's trait (70-90%), these values represent the expression of all possible morphological grades. When only a well-defined trait expression is considered (grades 5th, 6th and 7th), the frequency is much lower, not more than 19.2% for the 5th grade, and significantly less for the 6th and 7th grades. Our observations based on the study of the Croatian (Central European) populations show the highest frequencies for grade of the trait (exceeding 23%). Comparative data for European or European derived populations demonstrate significant variation in grade expression. While the previously published data suggest that the highest grade of the trait expression does not exceed 10%, our figures show the highest yet known frequency of a well-defined trait.