Researchers compared the brains of recently deceased people who had schizophrenia with those of recently deceased people who did not have schizophrenia  They found that 35 percent of the former and none of the latter showed evidence of damage to a structure of nerve cells called the subplate
They knew that this damage must have occurred prior to the second fetal trimester, when the subplate controls the development of the connections between the different parts of the brain
There may be a cause of schizophrenia that predates birth.