If you truly love your fiance' that should not matter. If you want children, there are other options. There is genetic counseling to find out the chances of your children being born with whatever the disease is. If the chance is too high, there is a sperm donor or adoption. Love is supposed to be unconditional! If you don't love him enough to accept this new information and don't want to marry him, then don't. Your love isn't unconditional then and you should move on and let him find some one who loves him unconditionally! Sometimes the truth hurts! I carry a genetic disorder and am blessed with a wonderful husband and two biological children. It is unfortunate that we did not know I carried the disorder before we chose to have children, but they are wonderful and loving and I wouldn't change a thing NOW. If I knew before, we probably would have adopted, sparing our children lives with Tourette 's Syndrome. I do know my husband would have still married me!