Objective: Delusional-like experiences (DLE) are common in the general community and are associated with a family history of mental illness. The aim of this study was to estimate the heritability of DLE.
Method: The Peter’s Delusional Inventory (PDI) was administered to a population-based cohort of mothers (n = 2861, aged 35–67 years) and their adult offspring (n = 3079, aged 18–23 years). Heritability of DLE was estimated from the sum scores of the 21 item PDI under the assumption that the covariance between mother–offspring scores is attributable to shared additive genetic factors.
Results: The means (medians and standard deviations) for the total PDI scores for the mothers and their offspring were 3.6 (3.0, 3.0) and 5.0 (4.0, 3.5), respectively. The Pearson correlation coefficient between mother and offspring PDI scores was 0.17 (P < 0.001). The heritability was estimated to be 0.35 (standard error 0.04).
Conclusion: Heritable factors contribute to over a third of the variance of PDI scores in this population. In light of the association between a family history of a wide range of mental disorders and DLE, these experiences may represent a useful quantitative endophenotype for genetic studies of common mental disorders in population settings.