If someone is MTHFR homozygous 677 (two copies of C677T), and their homocysteine level is normal, can MTHFR still cause cardiovascular problems? If so, HOW?? My parents and I are all homozygous 677. My dad had an occasional rapid heartbeat for decades; I had a large blood clot on my placenta during a recent pregnancy; and my mom has a huge blockage in an artery in front of her heart that is requiring open heart bypass surgery. We all have very normal homocysteine, eat healthy and have healthy weights. I don't think doctors will say there's a connection with MTHFR. Maybe I'm jumping to conclusions, but I can't help but wonder if there is a connection. This is my first post here at Phoenix Rising, and I have seen that many people here seem to be very knowledgeable about MTHFR.