For example, in sarcopenia patients, the X allele of the alpha-actinin-3 (ACTN3) genotype was found to be more associated with decreased thigh muscle volume compared with the RR allele of the ACTN3 genotype.5 In addition, angiotensin I-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism has been associated with improvements in performance and exercise duration in a variety of populations. The gene discussed is ACTN3; the disease is sarcopenia.