Unfortunately there is a good chance that your sister has RA, although it is not 100%. I believe the chance is about 40-60% in most studies. Since identical twins share 100% of their genetic makeup, this suggests that there needs to be other factors beyond genes for RA to develop. There is a consortium of researchers looking at the genetics of RA. I believe that they are looking for DNA samples of twins with RA. The studies are based at the North Shore Hospital in NY. You might ask your rheumatologist to consider entering you into one of those studies.
Is Rheumatoid Arthritis Hereditary?
I have RA for 3 years now. My mother also has RA. I have an identical twin sister who has been complaining that she is stiff and sore lately. What is the chances that she could have RA and where can I find more information about twins with RA?