A gene variant that affects skeletal muscle function may have protected humans against lower temperatures as they migrated from Africa to Europe more than 50,000 years ago, suggests a study published online on February 17, 2021 in the American Journal of Human Genetics. The loss-of-function (LOF) variant of the ACTN3 gene is known to result in the loss of a skeletal muscle protein called α-actinin-3 and to have become more prevalent as modern humans moved to colder environments. Researchers now show that α-actinin-3 deficiency improves cold tolerance in humans by increasing muscle tone. "Our study shows an improved cold tolerance in people lacking α-actinin-3, which would have been an evolutionary survival advantage when moving to colder climates," says co-senior study author Professor Håkan Westerblad, PhD, of the Karolinska Institutet. "Our study also highlights the great importance of skeletal muscle as a heat generator in humans." The open-access AJHG article is titled “Loss of α-Actinin-3 During Human Evolution Provides Superior Cold Resilience and Muscle Heat Generation.” Approximately 1.5 billion people worldwide (~20%) carry the ACTN3 LOF variant and therefore lack α-actinin-3. Although deficiency in this protein is not associated with muscle disease, such deficiency impairs performance during power and sprint activities. Because the LOF variant became more abundant as humans moved to colder climates, Professor Westerblad and co-senior study author Marius Brazaitis, PhD, of Lithuanian Sports University suspected that it might play a role in improving cold tolerance.
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