C4B and systemic lupus erythematosus: It would be desirable to elucidate the C4 gene copy numbers among aPL-positive subjects for a prevention purpose, as those with low total C4 or C4A gene copy number would have a higher risk to develop SLE, and high C4B GCN would have greater risk for complement-mediated complications such as thrombosis, recurrent pregnancy loss in females, and tissue injuries.