Schizophrenia is a serious mental illness classified as a psychotic disorder. Psychosis affects a person’s thinking, perceptions, and sense of self.
According to the National Alliance on Mental Illness (NAMI), schizophrenia affects approximately 1 percent of the U.S. population, slightly more males than females.
Having a first degree relative (FDR) with schizophrenia is one of the greatest risks for the disorder.
While the risk is 1 percent in the general population, having an FDR such as a parent or sibling with schizophrenia increases the risk to 10 percent.
The risk jumps to 50 percent if both parents have been diagnosed with schizophrenia, while the risk is 40 to 65 percent if an identical twin has been diagnosed with condition.
A 2017 study from Denmark based on nationwide data on over 30,000 twins estimates the heritability of schizophrenia at 79 percent.
The study concluded that, based on the risk of 33 percent for identical twins, the vulnerability for schizophrenia isn’t solely based on genetic factors.
Although the risk of schizophrenia is higher for family members, the Genetics Home Reference indicates that most people with a close relative with schizophrenia will not develop the disorder themselves.
Along with genetics, other potential causes of schizophrenia include:
- The environment. Being exposed to viruses or toxins, or experiencing malnutrition before birth, can increase the risk of schizophrenia.
- Brain chemistry. Issues with brain chemicals, such as the neurotransmitters dopamine and glutamate, may contribute to schizophrenia.
- Substance use. Teen and young adult use of mind-altering (psychoactive or psychotropic) drugs may increase the risk of schizophrenia.
- Immune system activation. Schizophrenia can also be connected to autoimmune diseases or inflammation.
Prior to 2013, schizophrenia was divided into five subtypes as separate diagnostic categories. Schizophrenia is now one diagnosis.
Although the subtypes are no longer used in clinical diagnosis, the names of the subtypes may be known for people diagnosed prior to the DSM-5 (in 2013). These classic subtypes included:
- paranoid, with symptoms such as delusions, hallucinations, and disorganized speech
- hebephrenic or disorganized, with symptoms such as flat affect, speech disturbances, and disorganized thinking
- undifferentiated, with symptoms displaying behaviors applicable to more than one type
- residual, with symptoms that have lessened in intensity since a previous diagnosis
- catatonic, with symptoms of immobility, mutism, or stupor
According to the DSM-5, to be diagnosed with schizophrenia, two or more of the following must be present during a 1-month period.
At least one must be numbers 1, 2, or 3 on the list:
- disorganized speech
- grossly disorganized or catatonic behavior
- negative symptoms (diminished emotional expression or motivation)
DSM-5 is the Diagnostic and Statistical Manual of Mental Disorders IV, the guide published by the American Psychiatric Association and used by healthcare professionals for the diagnosis of mental disorders.
Research has shown that heredity or genetics can be an important contributing factor for the development of schizophrenia.
Although the exact cause of this complex disorder is unknown, people who have relatives with schizophrenia tend to have a higher risk for developing it.