C4B and systemic lupus erythematosus: IgA deficiency is caused by C4B mutation and a deficiency of CYP21B results in congenital adrenal hyperplasia.14 The development of autoimmune hemolytic anemia and autoimmune thrombocytopenia is not infrequent in patients with selective IgA defiency 15–17 and SLE.18 Adult patients with SLE were more hypermobile (48%) than a control group (15%).19 This suggests a pathogenetic relationship between Evans syndrome, not infrequently present with SLE, and joint hypermobility.