A POPULATION GENETIC-STUDY OF PSORIASIS

We present epidemiological data for 5197 families with psoriasis. Erro rs in reporting have been analysed. Analysis of the data provides indi cations of random mating with respect to whether the partner has the s kin disease or not. Data on psoriasis among parents, siblings and chil dren are provided, and particular attention has been paid to the age a t onset of psoriasis. Psoriasis was present in the parents of about 36 % of the probands. In families in which one or both parents have psori asis, the occurrence of the disease among the siblings does not provid e any information which differentiates between a dominant and recessiv e mode of inheritance, but is compatible with both. In families in whi ch neither parent had psoriasis, provided there was a proband with pso riasis, the probability of the siblings suffering from psoriasis was c lose to 0.25, indicating a recessive mode of inheritance. The distribu tion of psoriasis among the parents of all probands, and among the chi ldren of probands, was also compatible with this mode of inheritance. The prevalence of psoriasis in the elderly was estimated to be about 5 %, and the gene frequency in the whole population 25%. These findings show that, with regard to first-degree relatives, the inheritance of p soriasis can fit an autosomal recessive model. The concept of a recess ive mode of inheritance may be used as a basis for genetic counselling .