C4 nomenclature statement (1990).

A common and revised nomenclature of the allotypes of the fourth component (C4) of human complement has been proposed. It is based on the results of the C4 Reference Typing of the VIth Complement Genetics Workshop and Conference, Mainz, FRG, 1989, the previous C4 nomenclature and the guidelines for human gene nomenclature (ISGN). The designation of allotypes derives from their relative electrophoretic mobility, the distinction between C4A and C4B proteins from their relative hemolytic activity. Common alleles retain their single digit numeric designation, intermediate variants their two- or three-digit designations; newly discovered alleles should not interfere with already described variants. At least 13 C4A alleles, 16 C4B alleles as well as non-expressed genes at each C4 locus are presently known. There are also duplicated loci of each C4 gene; they should be designated by repetition of the locus symbol at the haplotype or genotype level. As a phenotype they will be placed in parenthesis without repetition of the locus symbol. Aberrant allotypes or hybrid genes should be explained by a special suffix. No special nomenclature is recommended for restriction fragment length polymorphisms. Their designation should follow the general rules of the ISGN.