FCGR3B copy number variation is associated with susceptibility to systemic, but not organ-specific, autoimmunity

Naturally occurring variation in gene copy number is increasingly recognized as a heritable source of susceptibility to genetically complex diseases. Here we report strong association between FCGR3B copy number and risk of systemic lupus erythematosus (P = 2.7 × 10−8), microscopic polyangiitis (P = 2.9 × 10−4) and Wegener's granulomatosis in two independent cohorts from the UK (P = 3 × 10−3) and France (P = 1.1 × 10−4). We did not observe this association in the organ-specific Graves' disease or Addison's disease. Our findings suggest that low FCGR3B copy number, and in particular complete FCGR3B deficiency, has a key role in the development of systemic autoimmunity.