Figure 1

Inheritance of psoriatic arthritis. Two families are shown in which psoriatic arthritis (half-filled shapes) appears to exhibit a different pattern of inheritance. In the first it appears that the disease is inherited as a simple dominant, although the absence of disease in the parents is not consistent with this. In the second, there is an interplay between the psoriasis phenotype (quarter-filled shapes) in the parent and child in the third generation, and the instances of psoriatic arthritis in the second.