Fears and phobias: reliability and heritability.

BACKGROUND: Familial factors, which are partly genetic, influence risk for phobias. Prior family and twin studies, however, were based on a single lifetime assessment, which may be only moderately reliable.

METHODS: We obtained, 8 years apart, two assessments of lifetime history of five unreasonable fears and phobias (agoraphobia and social, situational, animal and blood-injury phobia) from face-to-face and telephone interviews from 1708 individual female twins from a population-based registry. We also obtained, 1 month apart, test retest reliability on 192 twins. We fitted, using the program Mx, a measurement model that estimates the role of genetic and environmental risk factors correcting for measurement error.

RESULTS: Short-term reliability of the five phobias was modest (mean kappa = 0.46), but higher than long-term stability (mean kappa = 0.30). Unreliability occurred both for subject recall of unreasonable fears and for interviewer assessment of which fears constituted phobias. Examining fears and phobias together, in a multiple threshold model, results suggested that twin resemblance was due solely to genetic factors, with estimated total heritabilities, corrected for unreliability, of: any 43%, agoraphobia 67%, animal 47%, blood/injury 59%, situational 46% and social 51%. With the exception of animal phobia, similar results were obtained analysing phobias alone.

CONCLUSIONS: Lifetime histories of unreasonable fears and phobias assessed at personal interview have substantial unreliability. Correcting for unreliability, the liability to fears and their associated phobias is moderately heritable. Individual-specific environmental experiences play an important role in the development of phobias, while familial-environmental factors appear to be of little aetiological significance.