http://emedicine.medscape.com/article/1001872-overview#a0156 Estimates annual incidence at 1 per 2 million population. Elsewhere estimates are 1 per 1 million — these seem to place the lifetime risk at around 1 in 20,000 or .005%
http://www.medscape.com/viewarticle/736557 places lifetime risk of SLE at 0.9% for women and 0.2% for men.
The frequencies of the genotype vary greatly in populations worldwide, with Asians usually having a higher frequency of the FCGR2B I232T allele compared to Europeans. Anti-GBM disease is autoimmune, relatively uncommon, and causes rapid renal failure and lung bleeding and has been found to be associated with the FCGR2B I232T allele in the Chinese. SLE, also an autoimmune disorder that may affect skin, joints, kidney, brain and other organs and rheumatoid arthritis, which leads to long term inflammation of joints has found to be associated with FCGR2B I232T allele in Japanese and Thais. Additionally FCGR2B I232T found in the FCGR gene polymorphisms such as FCGR2A, FCGR2B, FCGR3A, and FCGR3B that have been reported to be associated with similar human autoimmune diseases.