CR2 and systemic lupus erythematosus: Nitric oxide synthase 3 (NOS3) and complement receptor type 2 (CR2) gene polymorphisms, single nucleotide polymorphisms (SNPs) of the adenosine triphosphate-binding cassette B1 (ABCB1) gene were significantly associated with risk of femoral head osteonecrosis in SLE.[20–22] Fourthly, deficiency of important immunoregulatory mediator Vitamin D, has been found to be associated with avascular ON in a pediatric lupus erythematosus trial.[3] Therefore, interaction of multiple risk factors in our case jointly promoted the formation of ON.