rs1815739 - The Speed Gene - Sprint vs. Endurance
Gene: ACTN3
rs1815739 (R577X) in ACTN3 determines whether you produce alpha-actinin-3, a protein found exclusively in fast-twitch muscle fibers. The X allele (T) creates a premature stop codon, eliminating production of this protein.
Genotype Interpretations
RR - Full alpha-actinin-3 production. Associated with sprint/power performance. Over-represented in Olympic sprinters
RX - Reduced alpha-actinin-3. Mixed athletic profile, good at both power and endurance activities
XX - No alpha-actinin-3. Muscle fibers shift toward endurance/slow-twitch type. Over-represented in elite endurance athletes
Population Context
The X allele frequency varies dramatically: ~18% in African populations (where sprint dominance is observed) vs ~25% European vs ~52% East Asian. Nearly absent in West African sprinters.
Clinical Relevance
No disease association. Purely performance-related. ACTN3 deficiency (XX) is common and not a medical condition. May slightly influence recovery time from eccentric exercise.
Sources
- [1] Yang N et al. (2003) Am J Hum Genet 73:627-31
- [2] North KN et al. (1999) Nat Genet 21:353-4
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