Mutation: Why Some People Don't Feel Cold?

Roughly 80,000 years ago, Homo sapiens began leaving the African homeland to discover what lies on the horizon. The great migration brought the first homo sapiens far east to Asia and around 42,000 years ago, to Europe.

While encountering frigid conditions, inevitably, the voyaging homo sapiens' metabolism evolved and adapted to different climates. But, the stability to withstand the cold was not an evenly distributed trait.

For decades, scientists have been seeking the answer to the age-old question: why some humans have better cold tolerance than others?

Studying Mutations: Why Some Modern Homo Sapiens Tolerate Cold

A study published in the American Journal of Human Genetics on February 17 announced the answer to the long-running mystery of human temperature endurance.

Researches suggest that people who lack alpha-actinin-3 protein in muscle fibers tend to tolerate coles temperatures better than those who do not carry the same genetic variant.

The lack of the protein causes "superior cold resilience," researchers say. The deficiency affects roughly 1 in 5 people.

In a study published in 2014, led by Mauritius Brazaitis, scientists from the Lithuanian Sports University and his colleagues attempted to unlock the mysteries of how the human body acclimates to severely low temperatures on parameters such as metabolic activity and stress hormones.

But the research was in vain.

Scientists began studying variations in ACTN3, discovering that roughly 1.5 billion people lacked the muscle fiber protein.

Why is ACTN3 Important?

Muscles are comprised of multiple fibers that resemble long steel cables. Proteins called myosin and actin make it possible for the muscle fibers to contract.

Myosin and actin proteins are tightly arranged on top of each other as elongated filaments. When muscles contracts, myosin proteins latch onto actin and pull its end of the fiber. Eventually, this causes muscles to move.

ACTN3 gene, also known as the "speed gene," plays a vital role in the myosin actin contraction of muscles.

Co-author of the study Hakan Westerblad says, "There are two types of muscle fibers--slow-twitch and fast-twitch. While slow-twitch fibers conserve energy, the latter consume more."

Alpha-actinin-3 proteins are only expressed in explosive muscle fibers and not in slow-twitch muscles.

Researchers suggest that people who have a deficiency in ACTN3 or have a loss of function ACTN3 gene are better at tolerating low temperatures than the slow-twitch muscle fibers.

To determine what causes cold tolerance, scientists recruited 42 male residents with either ACTN3 or the gene variant between ages 18-40 that led moderately active lifestyles of 2-hour exercises a week.

Participants were then submerged in 14 degree Celsius water for 20 minute periods. Findings show that 30% of the participants with ACTN3 could maintain body temperatures above 35.5 degrees Celsius.

While 69% with the gene variant could do so only after cold-water exposure.

Thousands of years of evolution have ensured that modern homo sapiens with alpha-actinin-3 protein deficiency would stay warm and maintain appropriate body temperatures by using as little energy as possible, which also means their muscles consume less energy than most.

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