Schizophrenia is a chronic psychological disorder that manifests in almost all domains of one's life. Along with the manifestation, the disorder also has an interestingly complex causal and risk factor. The role of both nature and nurture is seen in this disorder, of which none can be undermined. Schizophrenia is thus a result of the interplay of genetic, neurodevelopmental, psychosocial and cultural, psychological, and environmental factors, all of which may act as risk factors that increase vulnerability to Schizophrenia.
Genes are one of the fundamental causes of susceptibility to schizophrenia, but no one gene is alone responsible for the disorder. Rather many genes may lead to it. There also exists strong evidence of Schizophrenia running in families, which has been confirmed by family, twin, and adoption studies. Research shows that identical twins are most likely to share Schizophrenia, followed by fraternal twins, children, siblings, parents, half-siblings, grandchildren, and so on. This implies that a person whose parents had schizophrenia is more likely to suffer from it than children whose grandparents have the disorder.
Another set of genetic risk factors is molecular genetics which indicates that many genes work together to cause the vulnerability of schizophrenia. The COMT gene on chromosome 22 and some dopamine receptors genes predict vulnerability to the disorder. Further, endophenotypes and traits closely controlled by genes can also be used to infer the relationship between genes and schizophrenia, and such genes have been shown to have a strong association with the disorder.
These factors refer to factors about an individual's pregnancy, fetal, and infant period. These factors are closely related to genetic factors and impact both developments and genetic expression, thereby impacting the vulnerability of the disorder. These can be enumerated as follows:
Viral infection: Viral infection in mothers during pregnancy, especially in early trimesters, directly impacts the incidence of the disorder. This is because the antibodies produced in the mother's body to fight the virus may enter the placenta and damage the fetal brain, or inflammatory cytokines may be produced, which causes neurodevelopmental damage, or the virus itself may affect the fetus's development.
Rhesus (Rh) compatibility: Evidence shows that incompatibility between the Rh of mother and fetus (i.e., the mother being Rh -ve and fetus Rh +ve, or vice versa) may also increase the susceptibility to schizophrenia. This is due to increased chances of blood disease, oxygen deprivation, and hypoxia in the newborn.
Complicated pregnancy or delivery: Many complications like breech delivery, prolonged labor, umbilical cord around the neck, etc., affect the fetus and newborn and cause trauma like reduced oxygen supply which canlead to increased susceptibility to the disorder.
Prenatal nutritional deficiency: Lack of nutrition in mothers during pregnancy heightens the risks of schizophrenia. Thus, research reports increased incidence among children born during the famine.
Maternal stress: A mother who is under any stress or trauma, especially during the early trimesters of the prenatal cycle, increases the risk of Schizophrenia. This is because of stress hormones which may enter the placenta and affect the normal development of the fetus.
Investigation of the role of psychosocial factors as a risk factor for Schizophrenia has always been of great interest to psychologists, and theories about them have been in the literature since the first half of the twentieth century. The psychosocial factors can be understood under the following heads:
Role of the family: Many theories have been developed explaining the role of the family in causing schizophrenia. Some of them are Bateson's double bind theory and Brown's emotional expression theory. While the double bind theory has been rejected, emotional expression still holds considerable consensus. This theory suggests that the disorder's relapse incidence is strongly related to the emotional expression in the family, i.e., the family's environment (which includes criticism, hostility, and emotional overinvolvement). Further marital Skew and marital schism theory also explain how either skewed power division in the family (i.e., one partner being excessively dominant and the other submissive) or excessive contradiction of views and separation thoughts in parents’ act as major stress increasing susceptibility to psychotic disorders like schizophrenia. Overall, the family's environment impacts the disorder's vulnerability. Even adoption studies show that the child's environment plays an important role in deciding the expression of schizophrenic genes.
Urban lifestyle: Researchers propose a sociogenic hypothesis suggesting that cities precipitate psychosis in genetically vulnerable individuals by providing a stressful environment that is socially isolated and cognitively demanding. Further, increased pollution, toxins, and infectious agents may also impact the physiology and genes of urban dwellers. A report even suggests that the incidence of schizophrenia can be reduced by 30% simply if all individuals live in a rural setting.
Immigration: Immigration implies movement from one place to another. When a person immigrants, he/she experiences a change in environment, culture, climate, and other demands of the society. These can be very stressful and lead to excessive physiological and hormonal reactions leading to impairments in certain faculties like dopamine which may impact schizophrenia risk. Other elements of immigration-related stress are prejudice, social isolation, and discrimination that one may have to face.
Substance Abuse: Abuse of substances like cannabis has been very evidently linked with schizophrenia. Not only are schizophrenic patients more likely to abuse cannabis, but also those who abuse cannabis are way more susceptible to the disorder. This is because cannabis triggers psychotic symptoms. When a person with genetic vulnerability uses it, he/she activates agents like dopamine in several areas of the brain, leading to a higher risk of the disorder. Cannabis has been reported to act as a catalyst in progressive brain change in schizophrenic patients.
Socioeconomic status: Socioeconomic status impacts the vulnerability of the disorder due to malnutrition in both mother and child. Further, people living in lower socioeconomic status also experience greater amounts of stress, thereby increasing their susceptibility to the disorder.
Beyond the prenatal, psychosocial, and genetic risk factors, one's personal experiences like stress and trauma may also affect the incidence of this disorder. Interestingly, it has been observed that the incidence of schizophrenia is higher in children born in late winter/early spring. Further, psychological characteristics like resilience, health behavior, and social support may also decrease vulnerability to the disorder even if a genetic predisposition exists. However, one thing is clear no one risk factor alone is capable of causing the disorder, and only the interplay or combination of more than one factor provides a good breeding ground for Schizophrenia.