Based on clinical experience, I suspect that all dermatologists believe psoriasis generally "runs" in families and is often precipitated by environmental factors. This general impression has been repeatedly confirmed by abundant objective data in numerous published articles. Why then does the mode of inheritance remain controversial?

In support of the conclusion reached by Cutler et al in this issue of the Archives (see p 718), the results of other single family studies^1,2 indicate a simple dominant mode of inheritance. In contrast to these reports, population surveys such as those conducted by Lomholt³ and Watson et al⁴ arrive at different conclusions.

The reason for this discrepancy is most easily explained by a difference in the method of data gathering. In single family studies, most persons are examined for evidence of psoriasis by a trained observer, whereas, in population studies, data are often obtained from a single family member.