Hey there Fedora,
Unfortunately they are claiming that lupus nephritis is hereditary condition and most of us are terrified if someone in the family had something that is hereditary.
This is an autoimmune disease and until now no one can say why autoimmune diseases are appeared. Basically this means that your body started to fight against you and it is attacking healthy cells and healthy tissue.
The most common symptoms of this condition is high blood pressure, visible swellings, weight gain (but be careful about this one because you can gain weight for many other reasons) and dark urine.
If you are suspecting that you may be suffering from lupus nephritis go and see your doctor as soon as possible. after some tests you will know for sure.