Schizophrenia almost always comes about in young adults. The number of children under 10 who are diagnosed with what might be called schizophrenia in an older person is essentially zero. Every paper I have read on it states that it comes about as a combination of heredity and environmental factors, in young adults or teens at the earliest. I have never heard of anybody "born with it"--maybe you mean he was born into a family where it ran in their genes and later developed it?
But other mental diseases also develop in young people (or older) as a combination of heredity and environmental factors, which also have nothing to do with the occult.
Being unrelated to "occult" does not require a person to be "born with it" in any situation. But you also said there is a combination with heredity, so that actually implies they are somewhat born with it (in combination with environmental factors). So I'm really not sure what you're trying to say here.
As a clear example, regarding something that is not a mental illness but a degenerative disorder, Parkinson's (the nonfamilial type) is not hereditary, and no one is born with that. Nonetheless it is developed later in life in some people, God forbid, and has nothing to do with occult.