My personal experience leads me to strongly believe that people can be mentally ill without having been abused, the same way they can be born blind or deaf or with any other disability.
Modern science of mental health and neurology says otherwise -- in the vast majority if not all cases of mental illness
(exception made for provable congenital defects affecting the brain), there is always an environmental trigger associated. This is why there isn't a "schizophrenia gene", but rather genes that make people
propense to schizophrenia.
Well of course... just like every time you flip a coin
(exception made for all the times it lands tails) it lands heads!
Congenital means you're born with it. Some people have mental illness resulting from congenital defects affecting the brain, just like you said.