- The protein α-actinin-3 is absent in approximately 1.5 billion people worldwide
- Researchers believe a genetic mutation that may have arisen in prehistoric times, is responsible for the missing protein
- According to a recently published study, the absence of the protein helps people tolerate the cold better
Some 50,000 to 100,00 years ago, as the climate of Africa became drier, humans began to migrate to colder climates of Europe. To better adapt to the cold, the presence of a particular mutated gene increased in these humans. This particular gene codes for the protein α-actinin-3; found in fast-twitch skeletal muscle fibres. Mutation in the gene results in the absence of this protein. Now, a recently published research has found that the absence of muscle protein, α-actinin-3, enhances cold tolerance in people. The study is published in the American Journal of Human Genetics.
Researchers at Karolinska Institutet in Sweden and the Lithuanian Sports University recruited 42 men aged 18-40 years for the study. As part of the study, participants sat in cold water (14 °C) for 20-minute sessions, with 10-minute breaks in between. The sessions continued in this manner till their body temperatures dropped to 35.5 °C. While they underwent cold-water immersion, researchers measured electrical activity of the muscles and took muscle biopsies.
70% of People Lacking Muscle Protein Tolerate Cold Better
Results of the study revealed that 30% of people with muscle protein maintained their body temperature during the cold immersion. However, in comparison, nearly 70% of people who lacked the protein maintained their body temperature above 35.5 °C. Thus, the absence of α-actinin-3 resulted in a lower temperature decline.
Those with the muscle protein had increased activation of fast-twitch fibers. Moreover, people lacking the muscle protein had higher numbers of slow-twitch fibers. As a result, instead of shivering these people used energy-conserving ways to generate heat.
Although the study provides evidence for the protein’s role in adults, it is unclear how it affects cold tolerance in infants. Moreover, scientists have yet to figure out how α-actinin-3 deficiency affects the body’s response to various physical exercises.
Wyckelsma et al., Loss of a-actinin-3 during human evolution provides superior cold resilience and muscle heat generation, The American Journal of Human Genetics (2021), https://doi.org/10.1016/j.ajhg.2021.01.013