There was an observation about natural selection I heard a few months ago which is pretty obvious once you see it it: adaptations only matter during the period that you're fertile.

Mutations that increased long-term mental illness didn't matter if nobody lived past 30. Mutations that increased attractiveness but caused issues down the road would be selected for by definition.

In this case people with this gene would be actually available as mates, as opposed to the others who presumably tended to freeze to death.