According to an article posted by the NY Times, some people have a mutation that makes them not smell the common fish smell. Dr. Stefansson, founder of deCODE genetics, conducted a study where people were they asked participates to smell six pens with synthetic odors. A small group thought the fish smell, was actually caramel scented. This mutation effects the TAAR5 gene. This mutation actually appears more common in Icelanders, which they have not figured out why yet. In my opinion this discovery is very unique. Normally when people think of mutation, they think of something being physical or mental wrong with someone, when in relative the severity ranges. Not being able to smell fishy scent may be better, at least I wish I didn’t smell them.
Addition article with information: https://www.nature.com/articles/d41586-020-02832-1#:~:text=When%20exposed%20to%20the%20reek,fish%20can%20smell%20like%20caramel