Some doctors think it is a syndrome, or collection of diseases. It is also speculated that there is more than one gene. Researchers refer to this as polygenic. Perhaps one gene exists for the positive symptoms and one for the negative. To complicate matters further, schizophrenics frequently have other mental disorders such as depression, anxiety disorder and personality disorder.
Researchers also feel strongly that the disease has an environmental component.
Some of the theories under investigation are exposure to a virus, some form of nutritional deficiency where the body lacks, or is unable to metabolize a chemical, and obstetric complications during birth. In addition, researchers have determined that the use of illegal drugs and stress, while not a cause, can trigger symptoms. It has long been suspected that schizophrenia might be inherited. However, this suspicion had little impact on psychiatric research into genetic causes. Researchers focused on life events that were easily observable or could be evaluated through a life history.