C4B and systemic lupus erythematosus: Out of the 50 kindreds and excluding the probands described above, an additional 12 probands had rare variants in genes that are well accepted to cause monogenic SLE via either the complement pathway (C3, C4A and C4B) or via metabolism of nucleic acids (DNASE1, IFIH1, RNASEH2B, RNASEH2C and SAMHD1).