What causes lupus to happen?

NOT KNOWN...: No one knows the final "trigger-pull" that causes lupus. We do know genetics play some role. We do know that hormones play a major role (reason for female dominance and females rarely getting sle before puberty). But why some with similar factors get disease is not known at present.

Genes, environment: This answer will change as we know more about lupus. We believe that for a person to get lupus, from the limited genetic information we have now, about 10% is from known genetic causes and remaining 90% unknown genetic causes and environmental causes. Environmental causes are largely undefined but important. Think about this: only 30% of identical twins develop lupus together.