7th World Congress on Genetics Applied to Livestock Production, August 19-23, 2002, Montpellier, France CHARACTERIZATION OF THE EQUINE ANGIOTENSIN-CONVERTING ENZYME (ACE) GENE N. Ellis, I. Tammen, F.W. Nicholas and H.W. Raadsma ReproGen, Centre for Advanced Technologies in Animal Genetics and Reproduction, Faculty of Veterinary Science, The University of Sydney, Camden, Australia INTRODUCTION The genetic basis underlying most complex traits such as disease, conformation, reproductive ability and soundness are largely unknown in the horse. In racehorses athletic performance is of particular interest. Although genetic variation in athletic performance (racing ability) has been described, (Tolley et al., 1985 ; Williamson 1998) the identity of the genes contributing to this variation is largely unknown. Angiotensin converting enzyme (ACE) plays an important role in the renin-angiotensin system that is primarily responsible for blood pressure homeostasis. The enzyme is specifically involved in increasing blood pressure during conditions of physiological demand. The discovery of an intronic insertion/deletion (I/D) polymorphism in the gene encoding for this enzyme has prompted many association studies. These studies have indicated a relationship between the polymorphism and differences in susceptibility to a number of conditions such as hypertension, cardiac disease, myocardial infarction, left ventricular hypertrophy and renal disease (Schunkert 1997). Furthermore, three groups have also reported on an association of the insertion allele with elite endurance performance in human athletes. Athletes, including Olympic rowers (Gayagay et al., 1998), mountaineers (Montgomery et al., 1998), cyclists and long distance runners (Alvarez et al., 2000) were all selected due to the superior oxygen metabolism required for their sport. The insertion allele was seen in much higher frequency in these athletes than in the normal population. Further studies have since shown an additional association of the insertion allele with an improved anabolic response to physical training (Montgomery et al., 1999 ; Williams et al., 2000). The insertion, an alu repeat, occurs in intron 16 of the angiotensin converting enzyme gene. Since alu repeats are repetitive DNA sequences and the polymorphism is within an intron, it is unlikely that the insertion/deletion polymorphism is the causative mutation in the human ACE gene. It is for this reason that it is thought to be a marker for as yet unidentified mutations that cause the differences observed. From human association and physiological studies the equine homologue of ACE was therefore identified as a candidate gene for contributing to genetic variation in racing performance. The purpose of this study is to characterize the equine angiotensin-converting enzyme gene and perform an association study to investigate links between this gene and equine athletic performance. Session 05. Horse breeding Communication N° 05-07