Graying Hair? Relax in the Cold

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Functional studies (here, here, and here) indicate that this allele produces an enzyme that has totally normal activity at 31 C (87.8 F), but at 37 C (98.6 F) it loses 75% of its copper-binding activity and at least 75% if not all of its enzymatic activity.  This indicates that the allele confers thermolability on the enzyme, making it intolerant to heat to the extent that normal body temperature impairs it. This is a common theme in enzymatic impairments.  31C is cold enough for hypothermia, and maintaining body temperature at that point is not a viable strategy to prevent hair graying.

Indeed, high body temperature helps all enzymatic reactions occur more effectively if the enzymes do not have impairments that make them thermolabile. For example, the wild-type allele for tyrosinase operates more effectively at 43 C (109.4 F) than at body temperature, but this is above the threshold of fever (41-42 C, 105.9-10.7.6F) that can cause brain damage and become life-threatening.

Maintaining supraphysiological copper concentrations is also not a viable strategy for preventing hair graying because high concentrations of free copper are toxic. In fact, they cause oxidative stress, which can lead to hydrogen peroxide production, which can destroy hair pigment and cause graying.

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This SNP is very common in people with European ancestry, where just under 40% of people are heterozygous and 7.6% are homozygous. It is not found in many Asians. It is found in American Blacks and Latin Americans, but not in African pygmies or Australian Aborigines, leading to speculation that it arose in Caucasians and spread to other groups through admixture.