36.4: Risk Factors For Developing Schizophrenia

It is clear that there are important genetic contributions to the likelihood that someone will develop schizophrenia, with consistent evidence from family, twin, and adoption studies. (Sullivan et al., 2003). However, there is no “schizophrenia gene,” and it is likely that the genetic risk for schizophrenia reflects the summation of many different genes that each contribute something to the likelihood of developing psycho- sis (Gottesman & Shields, 1967; Owen et al., 2010). Further, schizophrenia is a very heterogeneous disorder, which means that two different people with “schizophrenia” may each have very different symptoms (e.g., one has hallucinations and delusions, the other has disorganized speech and negative symptoms). This makes it even more challenging to identify specific genes associated with risk for psychosis. Importantly, many studies also now suggest that at least some of the genes potentially associated with schizophrenia are also associated with other mental health conditions, including bipolar disorder, depression, and autism (Gejman et al., 2011; Kim et al., 2011; Owen et al., 2010; Rutter et al., 2006).

There are also a number of environmental factors that are associated with an increased risk of developing schizophrenia. For example, problems during pregnancy, such as ncreased stress, infection, malnutrition, and/or diabetes, have been associated with increased risk of schizophrenia. In addition, complications that occur at the time of birth and that cause hypoxia (lack of oxygen) are also associated with an increased risk for developing schizophrenia (Cannon et al., 2002; Miller et al., 2011). Children born to older fathers are also at a somewhat increased risk of developing schizophrenia. Furthermore, using cannabis increases risk for developing psychosis, especially if one has other risk factors (Casadio et al., 2011; Luzi et al., 2008). The likelihood of developing schizophrenia is also higher for children who grow up in urban settings (March et al., 2008) and for some minority ethnic groups (Bourque et al., 2011). Both of these factors may reflect higher social and environmental stress in these settings. Unfortunately, none of these risk factors is specific enough to be particularly useful in a clinical setting, and most people with these “risk” factors do not develop schizophrenia. However, together they are beginning to give us clues as the neurodevelopmental factors that may lead someone to be at an increased risk for developing this disease.

Figure \(\PageIndex{1}\): There are a number of genetic and environmental risk factors associated with higher likelihood of developing schizophrenia, including older fathers, complications during pregnancy/delivery, family history of schizophrenia, and growing up in an urban environment. [“back-to-school-939922” by Veronica Martinez/Pixabay is in the public domain.]

An important research area on risk for psychosis has been work with individuals who may be at “clinical high risk.” These are individuals who are showing attenuated (milder) symptoms of psychosis that have developed recently and who are experi- encing some distress or disability associated with these symptoms. When people with these types of symptoms are followed over time, about 35% of them develop a psychotic disorder (Cannon et al., 2008), most frequently schizophrenia (Fusar Poli et al., 2012). In order to identify these individuals, a new category of diagnosis, called “Attenuated Psychotic Syndrome,” was added to Section III (the section for disorders in need of further study) of the DSM-5 (see TABLE 36.2.1 for symptoms) (American Psychiatric Association [APA], 2013). However, adding this diagnostic category to the DSM-5 created a good deal of controversy (Batstra & Frances, 2012; Fusar-Poli & Yung, 2012). Many scientists and clinicians have been worried that including “risk” states in the DSM-5 would create mental disorders where none exist, that these individuals are often already seeking treatment for other problems, and that it is not clear that we have good treatments to stop these individuals from developing psychosis. However, the counterarguments have been that there is evidence that individuals with high-risk symptoms develop psychosis at a much higher rate than individuals with other types of psychiatric symptoms and that the inclusion of Attenuated Psychotic Syndrome in Section III will spur important research that might have clinical benefits. Further, there is some evidence that non-invasive treatments such as omega-3 fatty acids and intensive family intervention may help reduce the development of full-blown psychosis (Preti & Cella, 2010) in people who have high-risk symptoms.