Genetics

Schizophrenia unquestionably has a genetic component. Suspects include chromosomes 13, 22, and possibly 8. Individuals with a family predisposition to schizophrenia often have several structural brain abnormalities, including reduced brain size and enlarged ventricles. Researchers believe that some people inherit a biological predisposition to schizophrenia and develop the disorder later when they face extreme stress, usually during adolescence or early adulthood.  Studies of relatives have found repeatedly that schizophrenia is more common among relatives of people with the disorder.  The more closely the person is related, the greater the chance of developing schizophrenia.  In studies with twins, researchers found that if one identical twin develops schizophrenia, there is a 48 percent chance that the other twin will develop it as well.  If one fraternal twin has schizophrenia, the other twin has a 17 percent chance of developing the disorder. Family members and their schizophrenic relatives also have a higher incidence of common traits, like deficits in working (short-term) memory. Mixed-handedness (the use of different hands for different tasks), particularly in females, may also be an inherited trait linked to schizophrenia, as well as eye tracking dysfunction. However, heredity does not explain all cases of the disease. But, about 60% of people with schizophrenia have no close relatives with the illness.