Epidemiology and Genetics The prevalence of ra in China is approximately 0.3%o of the population a women are affected approximately three times more often than men 80% of all patients develop the disease between the ages of 35 and 50Epidemiology and Genetics  The prevalence of RA in China is approximately 0.3% of the population  women are affected approximately three times more often than men  80% of all patients develop the disease between the ages of 35 and 50