Phobia, Specific

Clinical Features

The DSM-IV (American Psychiatric Association, 1994) describes specific phobias, also known as simple phobias, as being characterized by a marked persistent, excessive, and unreasonable fear caused by the presence of a specific object or situation (e.g., flying, heights, animals, injections, blood). Exposure to the phobic stimulus provokes an immediate anxiety response often resembling panic (see panic disorder, 167870). An adult recognizes that the fear is excessive, but a child may not. The phobic situation is either avoided or endured with intense anxiety or distress, and the avoidance or anxiety interferes with the individual's life activities. Vasovagal fainting may occur and is particularly common with blood-injection-injury phobia. Epidemiology studies indicate that women are more likely to have specific phobias than men. The overall 1-year prevalence is 9%, with a lifetime prevalence of 10 to 11.3%. A genetic component to simple phobias has been hypothesized because the illness, especially blood injury phobias, may aggregate in families, and because most phobias are not associated with a previous traumatic event involving the phobic stimulus.

Mapping

In a genomewide linkage analysis of 57 European American patients with simple phobia from 14 families ascertained through probands with panic disorder, Gelernter et al. (2003) found evidence for linkage to chromosome 14. Parametric analysis yielded a maximum lod score of 3.17 (dominant model) and 2.86 (recessive model) at marker D14S75. Using a simple parametric model, the lod scores at D14S75 increased to 3.70 (dominant model) and 3.30 (recessive model). Gelernter et al. (2003) noted that several anxiety disorders segregated in these families and that several individuals with simple phobia also had other comorbid anxiety disorders. They also noted that the homologous genomic region has been implicated in a mouse model for fear.