Genetic and Environmental Influences on Anxiety Disorders: A Systematic Review of Their Onset and Development

Fear is an emotion most humans feel throughout their lifetime, often without knowing its exact cause. Fear is considered a behavioural act to escape a potentially threatening situation, whereas anxiety is distinguished by the lack of actual stimuli and, more so, the threat of potential stimuli. Fear and anxiety are two distinct emotions which warrant separate classifications. Understanding both the genetic and environmental influences which contribute to anxiety disorder onset and development can aid in prevention, diagnosis and management; it may also play a role in helping patients further understand their diagnosis and guide future research. This review examines genetic and environmental contributions to the onset and development of anxiety disorders and explores their implications for treatments and further research. An extensive search of databases, including PubMed, Web of Science and Google Scholar, using specific search terms led to the collection of a large number of studies prior to further screening. The inclusion criteria were: studies written in English, full-text available, human studies, and studies conducted within the last 10 years (at the time of writing). The exclusion criteria were: animal studies, studies with a focus on neurological anatomy rather than anxiety disorders, and studies including depressive or other psychological disorders. Using a cross-sectional approach allowed for the strengths to be summarised whilst considering the limitations of the research. The studies were screened for limitations and some of these were stated within the research, whilst others had to be interpreted using a subset of pre-formulated questions to ensure reproducibility. Variables such as the main outcomes, conclusions and limitations were tabulated to guide the interpretation of these studies. Genetic predispositions were linked to specific gene polymorphisms or familial abnormalities in neurological anatomy and often correlated with the likelihood of the onset of anxiety disorders or contributed to the severity of symptoms. Environmental influences were found to affect the functioning of the brain and some studies established the impacts that therapies have on brain function. The majority of studies have implicated that a combination of genetics and environment have an effect on anxiety disorders, with one study suggesting that a single traumatic event can lead to alterations in the function of specific genes related to anxiety disorders. Both genetic and environmental factors contribute to the onset, development and severity of anxiety disorders, with environmental triggers often influencing the phenotypic expression of these disorders. Further research would benefit from determining specific processes which lead to the onset of anxiety disorders to facilitate their detection and intervention before resulting in life-long and generational consequences. Studies including larger sample sizes and varied subjects would be advantageous in the future.