Hard to know for sure if mitral valve disease is hereditary, genetic, familial, which are not quite the same, but myxomatous degeneration surely runs in my family...
my father had mitral valve repair about age 60 (if I remember correctly), I am about to have a mitral valve repair (and I have A fib) at 62, and my 60 year old brother is in need of surgery as well. My 55 y o brother has mitral valve prolapse, as does my 34 year old daughter (who really needs a good cardiology work up, I think, and we are working on that). So, like everything else in medicine, sometimes things do tend to run in families.
But they also crop up de novo in people with no history...