National Alliance on Mental Illness
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The Causes of Schizophrenia
While an exact cause of schizophrenia is still unknown, researchers do know that the brains of people living with schizophrenia are different from those undiagnosed with the illness. It is too early to classify schizophrenia as either a neurodevelopmental (impairment of the growth and development of the brain) or a neurodegenerative (progressive loss of structure or function of neurons) disorder, as both seem to occur over the course of the illness. Research strongly suggests the emergence of schizophrenia is a result of both genetic and environmental factors.
Unlike other genetic conditions such as Huntington's or cystic fibrosis, it is believed that no one single gene causes the disease by itself but rather that several genes are associated with an increased risk of schizophrenia. While schizophrenia occurs in one percent of the general population, having a history of family psychosis greatly increases the risk. Schizophrenia occurs at roughly ten percent of people who have a first-degree relative with the disorder, i.e., a parent or sibling. However, the highest risk occurs when an identical twin is diagnosed with schizophrenia. The unaffected twin has a roughly 50 percent chance of developing the disorder.
The genetic component appears to extend beyond family environment. For example, children with a parent living with schizophrenia who were put up for early adoption still develop schizophrenia at a higher rate than the rest of the of the population.
Specific genes have been shown to influence the risk for developing schizophrenia. Despite many studies revealing a connection between particular genes and schizophrenia, other studies have found that those genes do not necessarily increase the risk of schizophrenia.
With advancements in gene technology, it may prove beneficial to speak with a genetic counselor that can provide information on the way their diagnosis or that of a relative relates to the rest of the family. It is important to note that the ability to discover genes that appear to lead to the exhibition of schizophrenia cannot be used to discriminate against individuals with schizophrenia or their family members when they are trying to obtain health insurance. In 2008, the Genetic Information Nondiscrimination Act (GINA) was signed into law and was designed to benefit both genetic research and to protect the privacy of those families affected.
Genetics, however, are not the whole story. Scientists believe that it takes more than just genes to cause schizophrenia. Environmental factors, such as exposure to viruses or malnutrition before birth and potentially psychosocial and socioeconomic factors all interact with epigenetic gene development. One potential cause that has gained traction in recent years is the effect of early childhood trauma. The epigenetic development of a gene, the way a gene changes over a lifetime, varies depending on environmental pressures. Epigenetic development can be thought of as a switch, turning on or off genes at certain points in life. Environmental factors can sometimes interfere with the natural process.
While many of environmental factors occur early in life, schizophrenia is not expressed generally until young adulthood because the brain undergoes major changes during puberty that may trigger psychotic symptoms.
Substance abuse is one particular environmental factor that has garnered much attention by the general public and scientific researchers alike. According to the National Institute of Mental Health, while some researchers do not believe that substance abuse causes schizophrenia, some do, stating that the comorbidity is above coincidence.
In recent years there have been new studies linking the smoking of marijuana to the earlier onset of schizophrenia, by perhaps triggering the illness in those with a genetic predisposition. The potential effects of marijuana on schizophrenia, however, have been known for many years. Additionally, people who abuse drugs are shown to be less likely to follow their treatment plan.
Brain chemistry and structure also play a pivotal role. Neurotransmitters, including glutamate and dopamine, are some of the main culprits scientists believe behind the occurrence of schizophrenia. Neurotransmitters are what the brain uses to communicate. Some scientists believe that problems during brain development in utero are the cause for these faulty connections.
Brain imaging technologies, such as fMRI, functional magnetic resonance imaging, and PET, positron emission tomography, which provide for a detailed map of the brain, have shown that individuals diagnosed with schizophrenia have changes in both brain structure and chemistry.
Brain structure is influenced by both environmental and genetic factors. For example, a 2001 study found that whole brain, gray matter and white matter are all largely influenced by genetic factors.
New research has continued to reveal that brain structure differences noticed between individuals with schizophrenia and those without differ particularly in the frontal lobe. However, most neuroimaging studies to date have not included non-medicated participants in their studies, thereby clouding whether it may in fact be the medicine themselves that are causing the changes in brain structure. Multiple studies have revealed that anti-psychotic drugs can result in measurable brain tissue loss. The authors of the studies note, however, that this is not a reason to stop taking antipsychotics, and that more research needs to be done.