So the truth really is that we don't know what the exact cause of rheumatoid arthritis is. We do believe it's multifactorial. There are some genetic and environmental factors that play a role. With the genetic factors, we've looked at something called the HLA DR4 that could account for some portion of the genetic risk for rheumatoid arthritis. We know that there's a familial risk. If you have a relative that has rheumatoid, certainly you could be at a higher risk for rheumatoid arthritis. However, there are people that have no family history of rheumatoid and they still develop rheumatoid arthritis. Environmental factors can also be a part. We know that smoking can worsen RA symptoms, sometimes bacterial infection or a viral infection can cause a rheumatoid arthritis flare. It's believed that some infection in the gums can cause flare, or cause rheumatoid arthritis. So these are all factors that we believe play a part in rheumatoid arthritis, but we don't really know exactly what brings on your first flare. And so there's still a lot of ongoing research to figure why some patients have rheumatoid arthritis.