Lupus turns the body's immune system against itself, attacking the skin, joints, and internal organs. One of the most serious complications is lupus nephritis, a disorder that causes loss of kidney function and manifests in about a third of the 1.5 million Americans—mainly women—who have lupus. No one knows what causes lupus nephritis to develop, and possible genetic roots have not been well studied. Now, doctors from the University of Florida think they may have found a genetic marker that predicts who might be at risk for lupus nephritis.

What the researchers wanted to know: Is there a genetic variation that predisposes people to lupus nephritis?

What they did: The researchers took blood and serum samples from 134 patients, about 90 percent of whom were women. Half of the patients had developed lupus nephritis. They analyzed all of the patients' DNA and compared it with the DNA of 118 healthy control subjects, looking for variations in genes that regulate the production of a specific type of protein, called MCP-1. People with lupus nephritis have increased levels of MCP-1 in their urine.

What they found: Two genetic variations greatly increase lupus nephritis by up to four times in lupus patients. These variations allow the body to produce high levels of MCP-1, though the scientists are not sure if MCP-1 production causes lupus nephritis. The lupus patients who did not have lupus nephritis did not have a gene pattern different from the healthy subjects, nor did they have higher levels of MCP-1 in their urine.

What it means to you: The authors hope that MCP-1 can be used as a marker for possible lupus nephritis. They suggest that screening for the gene types that increase MCP-1 levels be used in lupus patients as both a warning sign for possible kidney disease and a test for whether treatment is working.

Caveats: The scientists have found a strong association between two genetic variations, production of the MCP-1 protein, and lupus nephritis. That still does not mean that faulty genes or prolific proteins cause the kidney disorder.

Find out more: A doctor, not associated with this study, has written a detailed description of lupus nephritis on the Lupus Foundation of America's website.

Read the article: Tucci, M., Barnes, E.V., Sobel, E.S., Croker, B.P., Segal, M.S., Reeves, W.H., Richards, H.B. "Strong Association of a Functional Polymorphism in the Monocyte Chemoattractant Protein 1 Promoter Gene With Lupus Nephritis." Arthritis and Rheumatism. June 2004, Vol. 50, No. 6, pp. 1842–1849.

Abstract online: www3.interscience.wiley.com