Rheumatoid arthritis (RA) strikes three times more women than men and researchers in Europe may have found a clue.   Scientists at the Arthritis Research UK Epidemiology Unit at the U of Manchester have discovered 14 new genes that can lead to RA, adding to the 32 other genes that have already been identified.  The researchers latest study published in Nature Genetics, has reported genes that are specific to the female X-chromosome.  According to Professor Alan Silman, medical director at the Research Unit, "This is the first time that a genetic association has been established between RA and the X chromosome."