A perdisposition of a diease may happen because genes pass on from one generation to the next. This can be studied by Materson & Davis who found realtives of schizophrnics were 18x more likely to be diagnosed with schizophernia than we would normally expect.
Influenza and measles are caused by germs and microorganisims.
These may explain schizophrenia. Barrett et al found increased incidence of schizphrenia in children who's mothers had a flu when they were pregnant. Thereby suggesting that the cause of the disorder might be a disease.
This involves chemicals such as nerotransmitters. Too much or too little of a paricular neurotransmitter may produce pyschological disorders. For example an increased level of dompamine is linked to schizpherina - drugs likecocaine which increase dopamine levels can lead to schizophernia like symptoms.
The sturcture of the nervous system may explain the disorder amensia, this is because the part of the brain in which long term memories are stored is damaged. In the case of schizophrenics there is eveidence that past modern studies that their brains are different from those of a normalk individual. However we cannot be sure whether schizophrenia caused the nerotmical changes or whether the difference were the cause of the mental disorder.