ISSN 1022-7954, Russian Journal of Genetics, 2015, Vol. 51, No. 3, pp. 318–321. © Pleiades Publishing, Inc., 2015. 318 1 Creatine kinase (CK) catalyzes the reversible trans- fer of a phosphate from phosphocreatine to adenosine diphosphate, generating adenosine triphosphate in tissues such as brain and muscle that require large amounts of energy. The muscle-specific creatine kinase (CKMM) enzyme is one of several tissue-spe- cific isozymes of creatine kinase (CK) that play a vital role in energy homeostasis of muscle cells [1, 2]. It has been shown that CKMM activities differ with respect to skeletal muscle fiber types, and the type II (fast- twitch) fibers showed significantly higher CKMM activity than type I (slow-twitch) fibers [3, 4]. It has been suggested that CKMM reduced activity may be a characteristic feature of the skeletal muscle of endur- ance athletes [2, 3, 5]. In humans, the CKMM- encoding gene CKM has been mapped to chromosome 19q13.2–13.3 [6, 7]. Within the sequence of the CKM gene, more than 260 single nucleotide polymorphisms (SNPs) exist. Several studies have tried to link CKM gene polymorphisms with physical performance related phenotypes [2, 5, 8, 9]. However, only the A/G variation (rs8111989) located in the 3'-untranslated 1 The article is published in the original. region of the CKM gene, also known as the CKM-NcoI SNP, was found to be relevant in terms of genetic test- ing in sport. It was suggested that the CKM-NcoI poly- morphism might be associated with differential CKMM activities in myocytes [10]. Other authors have postulated that the CKM genotype may be associ- ated with the expression and stability of its mRNA [11]. Moreover, it has been reported that blood levels of creatine kinase (CK) may be used as a marker to reflect the magnitude of skeletal muscle destruction in response to exercise [12]. Such exertion-induced mus- cle injury causes an increase in blood CK and it was also revealed that some individuals exhibit extreme increases in blood CK after exercise—those people have been characterized as high responders (HR) [12]. It has been shown that athletes or individuals with the CKM-NcoI AA genotype had a six-fold higher likeli- hood of being HR compared with GG and AG geno- types. Because the G allele is the rare allele for the CKM-NcoI polymorphism, some have speculated that this allele is associated with a protective mechanism against exertional muscle breakdown [13]. Several articles have been published showing a positive associ- CKM Gene Polymorphism in Russian and Polish Rowers 1 J. Eider a , I. I. Ahmetov b, c, d , O. N. Fedotovskaya b , W. Moska e , P. Cieszczyk a , A. Zarebska e , Z. Czubek e , T. Klocek f , M. Stepien-Slodkowska a , A. Maciejewska-Karlowska a , and M. Sawczuk a a University of Szczecin, Faculty of Physical Culture and Health Promotion, Szczecin 71-065, Poland e-mail: jerzyeider@o2.pl b St. Petersburg Research Institute of Physical Culture, Sports Genetics Laboratory, St. Petersburg, 191040 Russia c Kazan State Medical University, Laboratory of Molecular Genetics, Kazan, 420012 Russia d Volga Region State Academy of Physical Culture, Sport and Tourism, Sport Technology Education Research Laboratory, Kazan, 420138 Russia e Academy of Physical Education and Sport, Faculty of Tourism and Recreation, Gdansk, 80-336 Poland f University School of Physical Education, Faculty of Physical Education and Sport, Krakow, 31-571 Poland Received April 29, 2014 Abstract—Muscle-specific creatine kinase (CKMM) plays a vital role in the energy homeostasis of muscle cells. The A/G variation (rs8111989) located in the 3'-untranslated region of the CKM gene has been found to be the most relevant in terms of genetic testing in sport. The aim of the presented study was to test the hypothesis that the G allele might represent a genetic element that contributes to the improvement of endur- ance performance in Polish and Russian rowers. The distribution of the CKM genotypes was examined in a group of Polish and Russian athletes in comparison with non-athlete controls. There were no statistical dif- ferences between the rowers and the control groups across the CKM genotypes when Polish or Russian par- ticipants were analyzed. Based on the obtained results, it may be speculated that the CKM A/G polymorphism is not an important determinant of endurance performance level in Polish and Russian rowers. However, these results should be interpreted with caution as they can be limited by many factors. DOI: 10.1134/S1022795415030023 SHORT COMMUNICATIONS