Association of ACTN 3 R 577 X but not ACE I / D gene variants with elite rugby 1 union player status and playing position 2 3

27 We aimed to quantify the ACE I/D and ACTN3 R577X (rs1815739) genetic variants in elite rugby 28 athletes (rugby union and league), compare genotype frequencies to controls and between 29 playing positions. The rugby athlete cohort consisted of 507 Caucasian men, including 431 rugby 30 union athletes that for some analyses were divided into backs and forwards and into specific 31 positional groups: front five, back row, half backs, centers and back three. Controls were 710 Caucasian 32 men and women. Real-time PCR of genomic DNA was used to determine genotypes using 33 TaqMan probes and groups were compared using Chi-square and odds ratio (OR) statistics. 34 Correction of p-values for multiple comparisons was according to Benjamini-Hochberg. There 35 was no difference in ACE I/D genotype between groups. ACTN3 XX genotype tended to be 36 underrepresented in rugby union backs (15.7%) compared to forwards (24.8%; P=0.06). 37 Interestingly, the 69 back three players (wings and full backs) in rugby union included only six XX genotype 38 individuals (8.7%), with the R allele more common in the back three (68.8%) than controls (58.0%; χ=6.672, 39 P=0.04; OR=1.60) and forwards (47.5%; χ=11.768, P=0.01; OR=2.00). Association of ACTN3 R577X with 40 playing position in elite rugby union athletes suggests inherited fatigue resistance is more prevalent in 41 forwards while inherited sprint ability is more prevalent in backs, especially wings and full backs. These 42 results also demonstrate the advantage of focusing genetic studies on a large cohort within a single sport, 43 especially when intra-sport positional differences exist, instead of combining several sports with varied 44 demands and athlete characteristics. 45