The onset of disease in twins and siblings with systemic lupus erythematosus.

We reviewed both the published cases of systemic lupus erythematosus (SLE) occurring in siblings as well as our own, in regard to the ages of onset and the calendar year of onset in the sibling pairs. These data were compared with the same data in non-consanguineous, noncohabiting matched control pairs of patients with SLE. Compared to the control patients, we found no tendency for cases in siblings to occur at the same age, but a significant tendency to occur close together in time, thereby implicating an environmental agent as either a causal or triggering factor leading to expression of the disease.