No, not everyone has the ACTN3 gene. The ACTN3 gene encodes a protein called alpha-actinin-3, which is primarily expressed in fast-twitch muscle fibers. The presence or absence of the ACTN3 gene varies among individuals due to genetic variation.
There are two common variants, or alleles, of the ACTN3 gene: the R allele (resulting in the presence of alpha-actinin-3) and the X allele (resulting in the absence of alpha-actinin-3). Each person inherits one copy of the ACTN3 gene from each parent, so individuals can have different combinations of alleles: RR (both copies of the gene are the R allele), RX (one R allele and one X allele), or XX (both copies of the gene are the X allele).
It is estimated that approximately 18-23% of individuals worldwide do not have a functional copy of the ACTN3 gene, meaning they have the XX genotype and lack alpha-actinin-3 in their fast-twitch muscle fibers. This genetic variation can have implications for muscle performance and athletic abilities, as alpha-actinin-3 is associated with enhanced muscle power and sprinting performance.
However, it's important to note that having the ACTN3 gene or its specific variants is just one factor among many that contribute to athletic performance. Other genetic, environmental, and lifestyle factors also play significant roles.