Factor B (BF) subtyping by isoelectric focusing: methods, nomenclatures, genetics and forensic application.

Usually factor B (BF) typing is performed by means of the traditional agarose gel electrophoresis. Using isoelectric focusing, the system can be extended by two common subtypes of BF F. The existence of BF F subtypes has in the meantime been confirmed by various authors and in different populations. Their inheritance has been proven by family- and mother/child analyses and molecular-genetic studies (correlation with restriction fragment length polymorphism). Different typing methods as well as different nomenclatures seem to indicate that the subtypes FA and FB (according to Geserick et al.) are identical with the Fb and Fa subtypes (according to Teng and Tan). At present, some confusion still exists for the less frequent variants and subtypes which possibly could be identified by direct comparison of the patterns. The BF system is a valuable marker in paternity testing. Its chance for exclusion of paternity in Caucasian populations has been calculated to be about 14% for agarose gel electrophoresis and increases to about 16% for BF F subtyping by isoelectric focusing. Preliminary results indicate that BF may also be used for typing of bloodstains (up to 2 weeks old).