We investigated by segregation anlysis the mode of inheritance of psoriasis vulgaris with 93 psoriatic families. Out of the 93, 7 families of normal x affected mating and 83 families of normal x normal mating were collected by single selection and 3 families of normal x affected mating were ascertained through parents (complete selection). Out of the 83, 9 have two or more affected children. The hypotheses of single locus models (single dominant and single recessive models) for psoriasis were ruled out from the results of χ2 analysis. On the other hand, the multifactorial model for psoriasis was not rejected by using Edwards' simulation model. The double recessive model, as one of the polygenic models for susceptibility to psoriasis was acceptable, determined in 9 multiplex families with psoriasis. Major genes having major effects related to psoriasis were not evidenced.
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