Family history of psoriasis and age at disease onset in Italian patients with psoriasis

Conflicts of interest: none declared. Sir, Familial occurrence of psoriasis has long been recognized. Frequencies of a family history of psoriasis range from 2·0% to 91·0%, with the variation probably due to differences in patient selection and methods used to assess the family history.1, 2 A family history of psoriasis has been associated with early‐onset psoriasis, the presence of HLA‐Cw*0602 and a more unstable and severe clinical course compared with patients with late‐onset psoriasis.3 4–5 The aim of our study was to describe the distribution of frequency, by age groups, of familial occurrence of psoriasis in an Italian population and to analyse its relationship with age at disease onset. From December 2004 to January 2006, 1420 patients with psoriasis, attending 21 Departments of Dermatology in northern, central and southern Italy, were invited to participate in this study. The estimate of sample size was performed using the following parameters: sample error E = 0·026, the event occurrence proportion P = 0·5 (in the case of maximum variability), probability 1 –α = 0·95. Approximately 3% of the subjects refused to be interviewed.