Having a sibling with severe medical problems definitely causes relational trauma. Less time & attention to go around. My other sister and I fought like crazy, but never with my little sister, so we ended up taking things out on each other when we were mad at her or our parents, etc. I lived in a different world from all the other kids at school because I was worried about real, grown-up problems like insurance not paying for necessary medications or equipment. No one else understood me. It definitely affects trust and the ability to get close with others.