From what my Oncologist says, no one knows exactly what causes this mutation. My research chemistry friend says these mutations are caused by a typo in the DNA. This one generally occurs during a person's lifetime and is rarely inherited from one's parents. I think of it as bad luck! In my case, I believe it first developed in my mid-30s. Something changed then that made me allergic to cinnamon and certain brands of soap and caused chronic circulation problems in my lower legs. That last one is according to a Hematologist. I don't know for sure the circulation problem led to this mutation, but within the medical community, I've known people who believe that people who develop this particular type of lower leg circulation problem are more susceptible to developing lung cancer later. That's total speculation, though. I was diagnosed with multiple blood clots and bilateral (both lungs) pulmonary embolisms in 2016 and cancer in 2018. I'm participating in a genomic study being run by my Cancer Center in the hopes of better understanding this mutation in the future.