Causes

A person's genetics, biochemistry, environment, history, and psychological profile all seem to contribute to the development of anxiety disorders. Most people with these disorders seem to have a biological vulnerability to stress, making them more susceptible to environmental stimuli than the rest of the population.

Biochemical Factors

Abnormalities in the Brain. Scientists are using imaging techniques, particularly magnetic resonance imaging (MRI), to identify different areas of the brain associated with anxiety responses.

Important research in anxiety disorders is focusing on changes in the amygdala, which is sometimes referred to as the "fear center." This part of the brain regulates fear, memory, and emotion and coordinates these resources with heart rate, blood pressure, and other physical responses to stressful events. Some evidence suggests that the amygdala in people with anxiety disorders is highly sensitive to novel or unfamiliar situations and reacts with a high stress response.

Obsessive-compulsive disorder (OCD) is the anxiety disorder most strongly associated with specific brain dysfunction. For example, abnormalities in a specific pathway of nerves have been linked to OCD, attention deficit disorder, and Tourette’s syndrome. The symptoms of the three disorders are similar and they often coexist.

A number of imaging studies have reported less volume in the hippocampus in people with post-traumatic stress disorder. This important region is related to emotion and memory storage.

Neurotransmitters. Studies suggest that an imbalance of certain substances called neurotransmitters (chemical messengers in the brain) may contribute to anxiety disorders. The neurotransmitters targeted in anxiety disorders are gamma-aminobutyric acid (GABA), serotonin, dopamine, and epinephrine. Serotonin appears to be specifically important in feelings of well-being, and deficiencies are highly related to anxiety and depression.

Examples of study findings on some neurotransmitters are: • Abnormalities in the neurotransmitters gamma-aminobutyric acid (GABA) and serotonin may have a particular role in susceptibility to generalized anxiety disorder. GABA helps prevent nerve cells from over-firing and serotonin is a brain chemical important in feelings of well-being. • Serotonin is a major player in OCD. • Changes in serotonin and dopamine have been observed in social phobia. • People with post-traumatic stress disorder have abnormalities in stress hormones (cortisol) and neurotransmitters associated with stress (epinephrine and norepinephrine). Such imbalances could account for the higher anxiety levels and a tendency to startle easily after a threat in people with PTSD.

Corticotropin-releasing factor (CRF), which is believed to be a stress hormone and a neurotransmitter, is thought to be involved in depression and anxiety by causing changes in serotonin levels.

Abnormalities in Breathing Functions. Many people, including children, with anxiety disorders are very sensitive to the effects of carbon dioxide (CO2). These people generally have higher than normal levels of cortisol -- the major stress hormone. In such cases, exposure to excessive CO2 causes these individuals to hyperventilate, in which their breathing becomes rapid and their heart rate quickens. The same response also occurs during danger. Over time, then, a series of such responses creates a pattern of impaired breathing and a sense of panic that evolves into a full-fledged anxiety disorder. Since CO2 is released from the lungs when people exhale, the condition may be aggravated in crowded spaces, such as airplanes or elevators.

Genetic Factors

Up to 50% of people with panic disorder and 40% of patients with generalized anxiety (GAD) have close relatives with the disorder. (About half of GAD patients also have family members with panic disorder, and about 30% have relatives with simple phobias.) One study reported the risk for inheriting a major phobia ranges from 25 - 37%.

Obsessive-compulsive disorder (OCD) is also strongly related to a family history of the disorder. Close relatives of people with OCD are up to 9 times more likely to develop OCD themselves. Researchers are making progress in identifying specific genetic factors that might contribute to an inherited risk. Of particular interest are genes that regulate specific neurotransmitters (brain chemical messengers), including serotonin and glutamate. In 2006, several important studies in the Archives of General Psychiatry suggested that the SLC1A1 gene, which is associated with glutamate regulation, may play an important role in early-onset OCD in boys. Research is also pinpointing regions on specific chromosomes (1, 3, 7, 6, 9, 15) that may contain genes linked to OCD.

Family Dynamics

The influence of the family on anxiety is complicated by both genetic and psychological factors.

Panic Disorder and Family Influence. Certain psychodynamic theories suggest, and a few studies support the idea, that some people may develop panic disorder if they cannot resolve the early childhood conflict of dependence vs. independence. In one study, for example, young adults who had experienced childhood anxiety were more likely to live with their parents until their early to mid-twenties. Many people with panic disorder perceive their parents as being extremely controlling and overly protective while showing little actual affection.

Phobias and Family Influence. Several studies show a strong correlation between a parent's fears and those of the offspring. Although an inherited trait may be present, some researchers believe that many children can "learn" fears and phobias, just by observing a parent or loved one's phobic or fearful reaction to an event. People who have social phobias and severe agoraphobia generally report less parental affection and more strictness, overprotection, and encouragement of dependence than those without these disorders. One 2000 study found similar traits in parents of children with social phobias. Such parents were also likely to have social phobias and depression.

Obsessive-Compulsive Disorder and Family Influence. One study found that parental influence played no part in obsessive-compulsive disorder if the OCD patient was also not suffering from depression. However, depression coexists in two-thirds of OCD patients, and in the study patients who had both OCD and depression reported lower levels of parental care and overprotectiveness.

Traumatic Events

Traumatic events generally trigger anxiety disorders in individuals who are susceptible to them because of psychological, genetic, or biochemical factors. The clearest example is post-traumatic stress disorder. Specific traumatic events in childhood, particularly those that threaten family integrity, such as spousal or child abuse, can also lead to other anxiety and emotional disorders. Some individuals may even have a biological propensity for specific phobias, for instance of spiders or snakes, that have been triggered and perpetuated after a single exposure.

Medical Conditions

Although no causal relationships have been established, certain medical conditions have been associated with panic disorder. They include migraines, obstructive sleep apnea, mitral valve prolapse, irritable bowel syndrome, chronic fatigue syndrome, and premenstrual syndrome.

PANDAS

The acronym PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcus) is a term for an autoimmune condition associated with group A streptococcal infection in children (the cause of "strep throat" and rheumatic fever). Children with PANDAS develop tic-related disorders, including OCD and Tourette’s syndrome. In such cases, the OCD symptoms develop abruptly soon after the infection. It is unlikely to be an important cause of OCD.