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.
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