Another study that seems to cement the damage theory of aging and disease. Genetically identical humans can express different diseases as they age. This particular study found that rheumatoid arthritis (RA) can develop in one twin and not the other. The researchers found 3 genes that are overexpressed in people who suffer RA.
Scientists compared gene expression patterns of 11 pairs of monozygotic twins, who shared the same egg and were genetically identical, but only one of them had RA. They found three new genes that were significantly over-expressed in the twin with RA compared to the one without the disease. This is the first report for RA that examines gene expression patterns in monozygotic twins.
"This is the crux of the issue we are trying to address in RA -- how two patients can have the same genes but different disease outcomes. Identical twins represent the best experimental system to address this question," says Joseph Holoshitz, M.D., an associate professor of internal medicine at U-M Medical School and co-author of the study.
The advantage of studying twins is that they start out with the exact same genetic information. Therefore, differences in gene expression are attributable to different environmental factors rather than genetics. Such factors could cause a random genetic mutation or affects how DNA is packaged.
"There's a lot of variability in the severity of the disease, symptoms, and the response a patient will have to treatment. Differences in the expression of genes caused by environmental factors that modify DNA have a lot to do with this variability," says Holoshitz.
