I don't know what to do.?

I am pregnant and I haven't told my boyfriend or my family. I never thought I would ever say this, but I want to have an abortion. The doctors told me that I would never have children, me thinking that I couldn't I never worried about it. The guy that I am pregnant for has so many disabilities in his family, his grandfather, 2 of his sisters,his uncle and aunt all have down syndrome. His cousin have sickle cell, his brother is a little person, and his cousin has a clef, and they have this skin disease when we were in high school kids use to tease some kids in his family calling them alligator skin. My boyfriend and one of his brothers are the only two that came out o.k. His mother is a little slow but she don't have down syndrome. I love him but I am so scared that something is wrong with this baby. I just found out Friday and I haven't told anyone, I don't know if I want to keep it. I don't know if I can handle