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The present work attempts to determine the distribution of CYP11A(TTTTA)n genotype and allele frequencies in 10 European and North African populations. This polymorphism has been associated with hyperandrogenism by several association studies. To our knowledge, this is the first study investigating the ethnic variation of this polymorphism. DNA was extracted from 868 whole-blood samples with the standard phenolchloroform technique, and PCR reactions were carried out using fluorescent primers as described previously. PCR products were analyzed by an ABI 3730 DNA Analyzer. A total of six alleles were identified, ranging from 220 bp (4 repeats [4R]) to 250 bp (10R). The most frequent allelic fragment size in all populations was 4R, with frequencies ranging from 47.9 (Sicily) to 62.8 (Tuscany and Germany). Allelic frequencies showed high heterogeneity between analyzed populations. We detected a significant gradient for alleles 4R and 8R. In this study, we report the allele frequency distribution of CYP11A(TTTTA)n showing a northsouth geographic gradient. This result could be useful for epidemiological studies about hyperandrogenism. [ABSTRACT FROM AUTHOR]