ABSTRACT
The inheritance of psoriasis was studied by analyzing data from 60 families of probands with psoriasis. 10 families were multiplex, and the other 50 were simplex. A significant higher frequency of the disease was found among relatives of probands than among general population, the frequency diminishing as the degree of relationship between relatives and probands descended. Collected data from the pedigrees of the families of probands did not conform to any simple mode of inheritance, and segregation analysis revealed frequencies of psoriasis among siblings of probands which are lower than expected for single gene defects. The results shown by the curve of liability of the relatives, the frequency in first degree relatives and the relative frequency in sibs points to a multifactorial inheritance. The heritability of liability for posriasis, which measures the relative contribution of genetic factors in etiology, was found to be 76.4%