Subaortic Membrane removal in 3 year old

My son, then 3 years old (now 8), was diagnosised with a subaortic membrane.  He had no symptoms, except for a heart murmur, however no outward symptoms before, nor since to this day.  He has yearly echos to watch the area for growth and check the pressure.  What are the estimated chances of his having to have valve replacement as he gets older?  Is this a genetic disease?  Do children grow up to have other related problems who have this surgery?  

[anomale]

Hi! I don't know anything about you and your son's situation but I would like to say that you seem to be a great mother to care so deeply about your son and to do your research. Our worried hearts will save the world one day! May peace and good health be with you and your son!