2 Answers

Lupus is a systemic autoimmune disease that has some genetic factors. It is also tied toenvironmental risk, which may determine whether people actually ever manifest the illness. These environmental factors may also play a role in the degree to which lupus may affect a person’s life and mortality. Thus while some people may have a genetic predisposition for the disease, not all those with genetic factors will get it. Read more here > http://www.wisegeek.com/is-lupus-a-genetic-disease.htm 

The cause for lupus is genetic since it has been found that the disease appears in certain families, and that when the disease appears in one of identical twins, the rates for the disease to appear in the other identical twin increase. Yet, the exact genes that cause lupus are not known as of now.
There are many environmental triggers needed for lupus to appear, which can differ in between patients. Such triggers are listed at
http://www.lupus.org/webmodules/webarticlesnet/templates/new_learnunderstanding.aspx?articleid=2233&zoneid=523