Key result
The ACTN3 R allele was significantly more common in elite rugby union back three players compared with controls (68.8% vs 58.0%; OR 1.60, P=0.04) and forwards (47.5%; OR 2.00, P=0.01).
Case-Control (n=1,217)
The ACTN3 R577X variant is associated with playing position in elite rugby union athletes, suggesting inherited sprint ability is more prevalent in backs and fatigue resistance in forwards.
ACTN3 R allele may associate with back-three positions in elite rugby; hypothesis-generating and requires replication before any selection or training implications.
We aimed to quantify the ACE I/D and ACTN3 R577X (rs1815739) genetic variants in elite rugby athletes (rugby union and league) and compare genotype frequencies to controls and between playing positions. The rugby athlete cohort consisted of 507 Caucasian men, including 431 rugby union athletes that for some analyses were divided into backs and forwards and into specific positional groups: front five, back row, half backs, centers, and back three. Controls were 710 Caucasian men and women. Real-time PCR of genomic DNA was used to determine genotypes using TaqMan probes and groups were compared using χ(2) and odds ratio (OR) statistics. Correction of P values for multiple comparisons was according to Benjamini-Hochberg. There was no difference in ACE I/D genotype between groups. ACTN3 XX genotype tended to be underrepresented in rugby union backs (15.7%) compared with forwards (24.8%, P = 0.06). Interestingly, the 69 back three players (wings and full backs) in rugby union included only six XX genotype individuals (8.7%), with the R allele more common in the back three (68.8%) than controls (58.0%; χ(2) = 6.672, P = 0.04; OR = 1.60) and forwards (47.5%; χ(2) = 11.768, P = 0.01; OR = 2.00). Association of ACTN3 R577X with playing position in elite rugby union athletes suggests inherited fatigue resistance is more prevalent in forwards, while inherited sprint ability is more prevalent in backs, especially wings and full backs. These results also demonstrate the advantage of focusing genetic studies on a large cohort within a single sport, especially when intrasport positional differences exist, instead of combining several sports with varied demands and athlete characteristics.
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Heffernan et al. (2016) conducted a case-control in Elite rugby union player status and playing position (n=1,217). ACTN3 R577X and ACE I/D gene variants vs. Controls and other playing positions was evaluated on ACTN3 R allele frequency (OR 1.60, p=0.04). The ACTN3 R allele was significantly more common in elite rugby union back three players compared with controls (68.8% vs 58.0%; OR 1.60, P=0.04) and forwards (47.5%; OR 2.00, P=0.01).
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