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Aetiology of panic disorder

Genetic factors

Evidence that panic disorder has a genetic component can be found in studies such as that by Kendler et al. who found concordance rates of 24 per cent between MZ twins, and 11 per cent between DZ twins. These and other data placed within a meta-analysis by Hettema et al. indicated that panic disorder has a heritability coefficient of 0.40. Specific genes related to panic disorder are now being identified. Kim et al., for example, have found a gene variant that controls the production of serotonin in the brain to be implicated.

Biological mechanisms

As with simple phobias, the central element of the panic response is a high level of physiological arousal, triggered by hypothalamic activity and mediated by the sympathetic nervous system. This response is driven by the neurotransmitter and hormone norepinephrine, and to a lesser extent epinephrine. Two further biochemical systems also seem implicated in the development of panic disorder. The effectiveness of tricyclics and SSRIs in treating the disorder as well as emerging genetic evidence has implicated the role of serotonin in the disorder. This has now been supported by neurological evidence of reduced production and post-synaptic binding along serotinergic pathways in the raphe, orbitofrontal cortex, temporal cortex and amygdala. The success of modern benzodiazepines in treating the condition has also implicated a role of GABA. The amygdala is involved in the generation of fear and its activity is largely controlled by GABA: low levels of GABA lead to high levels of fear.

GABA receptors also control activity within the hypothalamus, and hence the sympathetic nervous system.

Social factors

As with GAD, high levels of social stress increase risk for panic disorder. The highest rates of panic disorder are among those who are widowed, divorced or separated, live in cities, with limited education. They may also have experienced early parental loss and physical or sexual abuse (Ballenger 2000). Not surprisingly, childhood anxiety, which may be related to poor attachment with parents, also predicts panic disorder in adulthood (Biederman et al. 2005). However, Battaglia et al. suggested the link between childhood separation anxiety and adult panic disorder may be largely the result of common genetic factors rather than childhood separation anxiety being a cause of adult panic disorder.

Psychological explanations

Psychoanalytic and humanistic theories do not discriminate between panic disorder and GAD, and the models outlined in the section of GAD hold for both disorders. Both explanations also receive limited empirical support, as people with panic disorder frequently recall their parents being overly concerned and protective of them as a child. Mowrer’s (1947) model of fear acquisition and maintenance can provide only a partial explanation of panic disorder, as it assumes high levels of conditioned anxiety to be triggered by the presence of a feared stimulus. It has diffi culties in explaining high levels of anxiety in the absence of an obvious stimulus: a defi ning characteristic of panic disorder.

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