I am a HCM patient, not an expert. Your sister has HCM, so likely you also have 50% chance of having the mutated gene. If so, then your children have a 50% chance as well. However, the mutated gene may be present but not cause the conditions we call HCM, perhaps never manifest symptoms. Many repeated echocardiograms over years are primarily looking for heart muscle thickness and resultant restrictions to blood flow, etc. Seems to me a person can get the HCM question answered much faster and more efficiently with the genetic test. I would for sure see a HCM cardiologist for opinion and evaluation.