Genomic Analysis of the F Subtypes of Human Complement Factor B

Abstract

Factor B of human complement is encoded within the Major Histocompatibility Complex (MHC) and is polymorphic, with up to 30 alleles defined by electrophoretic mobility. One of the most common alleles, BF*F, is subdivided into the FA and FB subtypes, which differ at the gene level by non-synonymous base substitutions in the seventh codon. We have found at this position a new restriction site polymorphism, as a Bsl I site absent from the FB allele. Using this restriction polymorphism, we have developed a method for BF F subtype determination, based on amplification by polymerase chain reaction of the 5' end of the BF gene, and digestion with Bsl I. This new method has been applied to a panel of 29 selected BF F individuals. A single strand DNA conformation analysis of the same region of the gene allowed us to confirm the above DNA-based BF F subtyping. During this study, two BF*F1 alleles showed discrepancies between protein and DNA typing, which were confirmed by our sequencing data. These were identical, in the 5' region, to BF*S and BF*FB genes, respectively. In a comparison with two protein subtyping methods, identical results were found for only one third of the selected samples. The conflicting results may arise, in part, from previously undescribed molecular heterogeneity within BF F subtypes, or from the presence of a null allele. Our new method allows BF*F subtyping to be used with confidence in the definition of disease-associated MHC haplotypes.

Conserved extended haplotypes of the major histocompatibility complex: further characterization

“…This scheme does not reveal the genetic basis of extensive polymorphism at the protein level but distinguishes three predominant allelic groups: S, FA and FB. 124,125 The amplification primers were BFF 5 0 -GCC TCT TGT CTG GAG GTA AG and BFR 5 0 -GCA CAG GGT ACG GGT AGA AG, yielding a 252 bp fragment spanning exons 1 and 2 (annealing temperature: 561C). Restriction enzyme TaqI was used to distinguish BF*S from BF*F. Further characterization of BF*F subtypes (BF*FA and *FB) was achieved by BslI digestion.…”

Functional basis of protection against age-related macular degeneration conferred by a common polymorphism in complement factor B

“…Of particular interest are 3 common polymorphic variants of fB that differ at position 32 in the Ba domain (amino acid 7 in the mature protein; fB 32R , fB 32Q , and fB 32W ; rs12614 and rs641153) (8)(9)(10); fB 32R is the most frequent allele in Caucasians (allele frequency 0.79), and was originally described as fB-S (''slow,'' defined by electrophoretic mobility); the fB-F (''fast'') allele was further defined as fB-FA ( fB 32Q ; allele frequency 0.05) and fB-FB ( fB 32W ; allele frequency 0.16) (11). Factor B-S and fB-F have long been associated with various pathologies, including susceptibility to pathogenic infection, for example, with Trypanosoma cruzi, where fB-S is protective in cardiomyopathy associated with Chagas disease (12).…”

Sensitive and Specific Real-Time Polymerase Chain Reaction Assays to Accurately Determine Copy Number Variations (CNVs) of Human Complement C4A, C4B, C4-Long, C4-Short, and RCCX Modules: Elucidation of C4 CNVs in 50 Consanguineous Subjects with Defined HLA Genotypes

“…For example, AH47.1 (IHW-9047) with HLA B*4701, RCCX: L-C4A, DRB1*0701 is associated with congenital adrenal hyperplasia (5,62) (24,30,64). In-depth characterization of genetic variations of all MHC genes including the polymorphisms of complement factor B and C2 (65,66) and the constituents of RCCX modules using the consanguineous panel would prove highly informative and help the understanding of the genetic basis of MHC-associated diseases.…”