PAPARINI, A., M. RIPANI, G. D. GIORDANO, D. SANTONI, F. PIGOZZI, and V. ROMANO-SPICA. ACTN3 Genotyping byReal-Time PCR in the Italian Population and Athletes. Med. Sci. Sports Exerc., Vol. 39, No. 5, pp. 810–815, 2007. Purpose:Development of two novel sets of primers and probes to detect R577X and Q523R polymorphisms of the >-actinin-3 (ACTN3) geneby real-time PCR. We report the allelic frequencies observed in Italian individuals from the general population and athletes. Athleticperformance is influenced by training, environmental factors, and genetic predisposition. Actn3 belongs to a family of actin-bindingproteins and is supposed to influence sport performance. Methods: Primer-probe set design and protocol optimization for real-timePCR genotyping of R577X and Q523R polymorphisms. The assay was verified using a traditional PCR-RFLP approach and appliedon an Italian population sample (102 male subjects and 42 athletes). Results: Haplotype distribution confirmed the presence oflinkage disequilibrium between the polymorphisms, both in the Italian general population and athletes (respectively: W = 54.4, P e0.001 and W = 24.5, P e 0.001). Within the general population, a large percentage of homozygous subjects (21.6%) was deficient forActn3. No significant differences were observed in athletes. The concordance between PCR-RFLP and real-time PCR results was100 and 93% for polymorphisms Q523R and R577X, respectively. Conclusion: Real-time PCR represents an effective approachfor typing ACTN3 alleles. Allelic frequencies in the Italian population are consistent with those seen in other studies on Caucasians.