@Mor - I'm not sure that the two conditions are actually related. If your family is more likely to get urinary tract infections, it doesn't mean they will develop trigonitis. Researchers don't seem to know why anyone develops it.
In fact they don't know much about the condition at all and I don't think it is all that common. They don't have a reliable treatment for it yet either.
I think it is one of those names that is given to a condition which just happens sometimes, maybe because of another disease in the body, and at some point when they get a better grasp on it, they may even rename it or discover it is caused by more than one thing.