Both my dad and an uncle on my mother's side have UC. My dad had a colostomy in 1985 or so -- one of the first "reversible" colostomies performed in Canada. Others on both sides of my family have bad guts of various kinds.
My daughter started having seizures when she was about 5, and was diagnosed with epilepsy. There is nobody with epilepsy in either her dad's or my family, going back at least 3 generations. When we asked her neurologist what could have happened, she told us sometimes, these things are idiopathic. Just a completely unpredictable combination of her parents' chromosomes. These conditions have to start somewhere!