“Systemic lupus erythematosus, also called SLE or lupus, is a disease of the immune system that causes the immune system to attack tissues in various parts of the body.
The cause of lupus is unknown. Finding the cause is the object of major research efforts.
Factors that may contribute to the cause of lupus include viruses, environmental chemicals, and the person's genetic makeup.
Female hormones are believed to play a role in the development of lupus because women are affected more commonly than men. This is especially true of women during their reproductive years, a time when hormone levels are highest.
The observation that lupus may affect more than one member of the same family has raised the possibility that the tendency to develop lupus may be inherited. Having such a tendency, however, does not predict that a relative will develop lupus. About 10 percent of lupus patients have a close relative with lupus.”
Source: Cleveland Clinic health library
Further reading Wikipedia