Single Protein Defect May Cause Autoimmune Disease.

2001 JAN 11 - (NewsRx.com) -- Scientists have discovered that a single defect in a common protein causes a severe autoimmune disease resembling lupus - the debilitating, poorly understood malady that affects 100,000 people in the U.S., mostly young women.

The discovery points to a new drug target to treat a range of autoimmune diseases. The research by scientists at the University of California, San Francisco, combines genetic experiments in mice with studies of protein interactions.

Drawing on a refined understanding of how a wedge of atoms can convert molecular partners into antagonists, the new finding provides subtle but powerful evidence that lupus in humans might sometimes be an inherited disease with a simple genetic root, rather than an accumulation of a number of genetic defects as many have thought.

The study provides new evidence that a single genetic mutation can cause autoimmune disease, and also offers rare, compelling evidence that such a defect is dominant over the normal condition, making the genetic change hundreds to thousands of times more likely to cause disease than if it were a recessive trait. If a gene for a disease trait is dominant, a single copy of the gene can cause the malady, whereas if it is recessive, copies from both parents are required. Most previously identified genetic causes of autoimmune disease are recessive.

The finding also supports the view that what is called lupus may in fact be a collection of a number of different diseases with a common pathway, the scientists suggest. Their research showed that a lupus-like syndrome could result from a single amino acid change in a key protein on the surface of cells of the immune system. Known as a transmembrane receptor protein, this molecule normally receives signals from outside the cell and triggers internal responses. Since the protein is central to nearly all immune cells in humans as well as mice, the finding suggests that the range of symptoms associated with lupus - inflammation of heart and lungs, kidney failure, arthritis, and other forms of autoimmunity - could all derive from the single defect in the signaling pathway protein.

"Lupus is a devastating disease that affects one in every 2,000 people in the U.S. - and attacks nine females for every male," said Arthur Weiss, MD, PhD, Howard Hughes Medical Institute investigator and UCSF professor of medicine. "But while researchers have studied the disease intensively, the cause - or causes - have proven difficult to pin down. It may well be that at least part of the answer to the puzzle lies with a very small change in a signaling protein that underlies many different cell functions," he said.

Weiss is senior author on the paper describing the research in the December 22, 2000, issue of the journal Cell. Lead author is Ravindra Majeti, PhD, an MD/PhD candidate at UCSF working with Weiss.