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Specific Phobias |
Overcoming Anxiety (Home) > Specific Phobias > Prevalence, Natural Course, and Genetics Prevalence, Natural Course and GeneticsEpidemiological studies indicate that lifetime prevalence rates for specific phobias may be as high as 12%. This suggests that specific phobias belong to the most frequent mental disorders. In a community study by Costello (1982), it was found that animal fears (including fear of dogs, snakes, etc.) were the most prevalent, followed by nature (e.g., heights), and mutilation (e.g., injections) fears. In effect, animal fears occurred in nearly 43% of the women. Whether these fears represent clinical phobias remains unclear, but at the very least, Costello’s results suggest that mild specific phobias are widespread. This point is further underlined by the National Comorbidity Survey conducted by Magee and associates. These authors not only found a high lifetime prevalence rates for specific phobias (11.3%), but also noted that specific phobias are often associated with serious role impairment (i.e., interference with daily life), even though they usually go untreated. Another common finding in the literature is that specific phobias are diagnosed more often in women than in men. This is especially true for animal phobias. There are strong indications that this sex difference cannot be fully explained by assuming that it is more socially permissible for women to report fear than for men. Probably, other predisposing factors (e.g., sex hormones) contribute to the skewed sex distribution of fears and phobias. With regard to the natural course of specific phobia, Wittchen summarised the results of his longitudinal community study as follows: ‘‘The natural course of simple phobias is in the majority of cases chronic and can be characterised by the persistence of mild rather than severe symptoms of anxiety over decades. Only 16% remitted completely over the follow-up period of 7 years: thus, only very few spontaneous remissions could be observed’’. In passing, it should be noted that specific phobia often occur as a comorbid diagnosis in panic disorder and generalised anxiety disorder. Several family and twin studies have been carried out to explore to what extent genetic factors predispose to phobic fear. Briefly, family studies noted that relatives of probands with specific phobias have a threefold higher risk of specific phobias than control subjects. Likewise, twin studies show that the genetic contribution to specific phobias is significant though heredity can vary considerably for the different subtypes of specific phobias, with those for animal phobias being highest (32%) and those for situational phobias being relatively low. There is some discussion about the precise way in which genetic factors contribute to the aetiology of phobias. Although his review was not particularly focused on childhood phobias, his differentiation between eneral and specific genetic factors is very useful for the present discussion. According to Taylor , the general (i.e., higher-order) genetic factor constitutes the biological substrate of broad temperamental traits such as negative affectivity and neuroticism and acts as a vulnerability factor for a wide range of phobic fears. In contrast, specific (i.e., lower-order) factors predispose to certain circumscribed fears. Taylor summarised the role of both factors in phobic aetiology as follows: The general factor tended to make a modest contribution to agoraphobia, situational phobia, and social phobia (7-10% of variance; mean=9%) and a greater contribution to animal phobia (35%). Conversely, specific genetic factors were more important for agoraphobia, situational phobia, and social phobia (20-29%; mean=23%) compared to animal phobia (0%). The importance of general genetic factors in the aetiology of specific phobias becomes obvious when one looks at comorbidity studies. These studies show that having one specific phobia also increases the likelihood of experiencing subclinical fears from other phobia subtypes. The well-established fact that phobias tend to be strongly comorbid with each other has two important implications. First, it casts doubts on the preparedness hypothesis, inasmuch as this hypothesis assumes that evolutionary pressures have resulted in the genetic transmission of specific fears and phobias rather than a general trait. Second, this finding calls for studies that address the behavioural or temperamental manifestations of general genetic factors. Obvious candidates in this respect are neuroticism, negative affectivity, but also behavioural inhibition.
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