Is lupus hereditary?  

Somewhat hereditary? Sle (lupus) is an auto-immune disorder in which a person's immune system is reacting strongly against parts of his own body. The inflammation from the immune system reaction leads to symptoms. It is believed to be partly genetic or familial (some people may be genetically more likely to get sle) and partly environmental (something happens in a person's life that sets off the auto-immune reaction).
Yes. But how much of it is hereditary is unclear. From the limited genetic information that we have now (this is expanding as we speak), we think about 10% of lupus is genetic. This seems low, but this is with the limited data that we have. Also consider that identical twins where one has lupus, only 30% of the other twins will get lupus. These are non-genetic factors that play important roles also.