Genetic cause discovered for systemic lupus erythematosus

Mutations in a gene researchers call TREX1 is one cause for systemic lupus erythematosus (SLE), a severe and incurable autoimmune disease.

This is the result of a new study headed by Professor Norbert Hübner from the Max Delbrück Center for Molecular Medicine (MDC) Berlin-Buch and Dr. Min Ae Lee-Kirsch from the Technical University Dresden, (both in Germany) in collaboration with scientists from Finland, Sweden, the United Kingdom, and the USA. The study has now been published in the latest issue of Nature Genetics (Vol. 39, No. 9, pp. 1065-1067, 2007).

The exact causes for SLE are still unknown. Triggers are thought to include viruses, the sunlight, drug reactions, or a specific genetic predisposition. Symptoms of SLE can be inflammations of the skin, the joints, the heart, the lungs, the kidney, and the nervous system. The name of the disease refers to red spots on the skin which resemble the bites of a wolfe (latin: lupus). As the disease can affect any part of the body, it is “systemic”. SLE belongs to the group of autoimmune diseases, because the body’s immune system attacks its own healthy cells and tissues, causing inflammations. About 40,000 individuals are affected in Germany, most of them are women.

In a family suffering from a rare form of lupus, Dr. Lee-Kirsch and Professor Hübner discovered various mutations in the gene TREX1. Hence, they wanted to know if mutations in TREX1 also play a role in SLE, the most common form of lupus. Collecting blood samples from patients with SLE from the UK, Germany, and Finland, the researcher compared them with samples from healthy individuals. As suspected, patients with SLE carried mutations in the TREX1 gene whereas healthy individuals did not. Nevertheless, the mutations found in TREX1 are not responsible for all types of SLE.

The product of the gene TREX1 is a protein which plays a role in apoptosis, a program in which cells literally induce their own death when defective. Thus, apoptosis protects the body from harm. Once apoptosis starts, TREX1 gets rid of its junctions in the cytoplasm and translocates into the nucleus of a damaged cell to digest its DNA.

Mutations in TREX1, however, change part of the protein with which it is chained to the cell’s cytoplasm. In the case of apoptosis, TREX1 gets rid of its molecular chains, translocates into the cell’s nucleus, and spreads to other parts of the cell too. The immune system seems to be mislead as it produces autoantibodies against these cell particles and also against other healthy cells. Why autoantibodies are produced still remains unclear. “Further studies will have to shed light onto this problem“, stresses Professor Hübner.