I just wrote a paper that explores genetic and experiential causes of differences in the brain, and effects or symptoms associated with those differences. The genetic factors that I looked at were "Schizotaxia" - a set of schizophrenic-like symptoms, including negative symptoms but no positive symptoms, observed in first-degree relatives of people with schizophrenia; and DAMP syndrom - basically ADHD + developmental coordination disorder. I also discussed the effects of child abuse on the brain, and related outcomes seen in adult survivors of abuse and neglect.

Not only are there apparently genetic conditions that are associated with differences in the brain and outcomes in life, and which respond to medication, but similar differences are also seen in children who have been abused or neglected. Adult survivors even have the enlarged left ventricles and decreased left hippocampal volume similar to what is seen in schizophrenia. Adult survivors are also more likely to suffer disorders like PTSD when traumatized as adults than adults without a history of child abuse.

Other reading I've been into discusses how both epilepsy and bi-polar disorder, and probably depression too, can be kindled (created by inducing the symptoms at first), and each subsequent seizure or episode happens more easily, with less or no stimulus, and tends to be more severe.

Then there's the possibility that children with certain genetically-based predispositions that increase the likelihood of being victimized, and it all compounds each other. It's impossible at this point to say what causes what.