Mental illness is becoming increasingly prevalent in the United States. Nearly one in every five adults in the U.S. are diagnosed with some kind of mental illness, ranging in severity. 

There are many biological and environmental factors that may contribute to this increase, and there is still much research being done to study the physiology behind mental illness. More recent studies have found a potential link between autoimmune diseases and the onset of psychiatric disorders.

An autoimmune disease is a condition in which the immune system mistakenly attacks one’s own body. The immune system normally defends the body from foreign bacteria and viruses. In an autoimmune disease, the body cannot distinguish between healthy cells and foreign cells. Particular autoimmune diseases are known to have high frequencies of neuropsychiatric symptoms. 

“Psychiatric disorders are disorders of mind, thoughts, emotions and behaviors that impact  one’s functioning,” said Dr. Ritu Goel, a child and adolescent psychiatrist at Kaiser Permanente. “These vary from mild to moderate degrees and can range from a single episode to recurrent episodes or chronic conditions.”  

Many researchers have proposed that immune dysregulation and inflammation may link these pathological processes to psychiatric disorders. A recent meta-analysis found that a diagnosis of a non-neurological autoimmune disease increased the risk of later being diagnosed with a psychiatric disorder by 43%. Similarly, having a family history of autoimmune diseases increases the likelihood of schizophrenia by 10%. 

 “Multiple Sclerosis, for example, is often directly linked to the onset of depression and psychosis,” Goel said. 

Studies have found that 4% of patients with MS are also diagnosed with psychosis; this rate is much higher than that of the general population. Researchers identified many mechanisms that could explain the link between autoimmune diseases and the onset of psychiatric disorders. 

Immunological pathways may be linked to mental diseases because of the potential  dysregulation of different immune cells. For example, dysregulated levels of cytokines is common amongst people diagnosed with psychosis. 

Cytokines are a type of signaling cell that serves an important function in the immune system. In many people diagnosed with psychosis, inflammatory cytokine levels are increased and anti-inflammatory cytokine levels are decreased. 

Recent research has shown that the dysregulation of T cells, another essential component of the immune system, may have a positive correlation with mental disorders. Decreased levels of regulatory T cells are often associated with cognitive and neuropsychiatric symptoms.

Studies show that genetics may also play a role because many autoimmune diseases and psychiatric disorders are highly heritable. 

“The majority of psychiatric disorders have an association with certain defects of genes or chromosomes,” Goel said.

Schizophrenic patients, for example, are consistently found to have differences in genes known to be linked to the immune system. Similarly, several genes that increase likelihood of autoimmune diseases are often found within schizophrenic patients. More specifically, some discovered genetic loci in autoimmune diseases are found in the same chromosomal region as schizophrenia.

Researchers have speculated that those diagnosed with schizophrenia may also have a genetic predisposition for abnormal immune response to common pathogens. This may increase the susceptibility to autoimmune diseases for those diagnosed with schizophrenia. 

Infection has also been said to play a role in autoimmune diseases and psychiatric disorders. 

“Any infection of the brain can result in psychosis, delirium and memory loss, and many other bodily infections can lead to depression and anxiety,” Goel said.

Bacterial and viral functions increase the permeability of the blood to brain barrier, which strictly regulates the movement of ions and cells between the blood and the brain. This increased permeability leads to immune cells entering the central nervous system and ultimately cause inflammation of the brain. This inflammation is often associated with the onset of psychiatric disorders. 

Recent research has also pointed to autoantibodies as a possible immunological pathway to psychiatric disorders. Autoantibodies are immune proteins that target and react with a person’s own tissues and organs. 

One specific autoantibody targets a receptor in the brain called an N-Methyl-D-aspartate receptor (NMDAR). This receptor is associated with learning, memory and neuroplasticity, which is the ability of neural networks to change through growth and reorganization. When the autoantibody blocks the receptor from functioning properly, swelling of the brain and signal disruption can occur; this leads to prominent psychiatric symptoms including depression. These autoantibodies are detected within many people diagnosed with psychosis. 

The composition of the microbiome has been hypothesized to be essential to the development of both the central nervous system and the immune system, according to a study at Mental Health Centre Copenhagen. 

Gastric inflammation has been quite prevalent in patients diagnosed with autoimmune disorders. Microbial imbalance can affect the regulation of certain immune cells; studies have shown that this may play a role in the development of MS and celiac disease. 

Microbial imbalance can also increase the permeability of the gut-to-blood barrier which functions very similarly to the brain-to-blood barrier. This permeability is known as a “leaky gut” and is very prevalent in those diagnosed with schizophrenia. This increased permeability allows pathogens to enter the blood more easily, causing inflammation. Some studies even show that this can lead to neuroinflammation which increases the likelihood of both autoimmune and mental diseases. 

While this field is in its early stages, autoimmune diseases and immunological processes help shed some more light into the causes for psychiatric disorders.

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