AGE AT ONSET AND DIFFERENT TYPES OF PSORIASIS

The age at onset of psoriasis has been analysed for 11,366 psoriasis p atients. The age at onset for siblings of probands has been analysed f or 805 probands having one affected sibling and for 179 probands havin g two affected siblings. The age at onset curve for all probands shows a dominating maximum at about puberty but also indications for two mo re maxima at about 30 and 50 years of age, respectively. A more releva nt picture of the risk of getting psoriasis at different ages is obtai ned if the onset for old people having psoriasis is investigated. The three maxima come out more clearly in this case, and the puberty maxim um is not so dominating. For the families with one proband and two aff ected siblings there is a statistically significant correlation (P < 0 .001) between the age at onset of the proband and of the siblings, and also between the siblings, The correlation coefficient is between 0.3 0 and 0.45. For the probands with one affected sibling, the ages at on set of the siblings mainly fall in the same range as those of the prob ands. These data indicate three groups of patients with respect to age at onset. However, the overlap between the different groups is consid erable. The data presented are compatible with three, possibly genetic ally different, variants of psoriasis vulgaris. By studying the occurr ence of psoriasis among parents of the probands, the gene frequency ca n be estimated assuming a recessive mode of inheritance. It then turns out that the gene frequency of the group with the earliest age at ons et has a gene frequency of about 0.25, the next earliest, 0.18, and th e latest, 0.14.