Primary APS and SLE, although distinct entities [3], share several susceptibility genes [2] and clinical and serological characteristics: antiphospholipid antibodies (aPL) occur in 30–40% of SLE patients; antinuclear antibodies, Coombs-positivity and low complement levels are present in some primary APS patients; and APS nephropathy co-exists with lupus nephritis lesions in kidney biopsies from SLE/aPL-positive patients [7]. The gene discussed is FASLG; the disease is lupus nephritis.