Genetic basis for the 2D isoform patterns of CFHR1. (A) Electropherograms of CFHR1 exon 4 obtained from control persons presenting the CFHR1 2D isoform patterns A, B, and AB, respectively. The 3 nucleotide differences involving amino acid changes that distinguish the CFHR1*A and CFHR1*B alleles (c.469, c.475, and c.523) are shown. (B) Alignment of the homologous domains in CFHR1 (SCR3 to SCR5) and fH (SCR18 to SCR20). The amino acid differences between domains are indicated. SCR4 in CFHR1 and SCR19 in fH are identical. CFHR1A and CFHR1B isoforms differ in 3 amino acid residues located in the SCR3 domain (p.157, p.159, p.175); the theoretical pI is shown in brackets. The SCR3 domain in CFHR1B is identical to the SCR18 domain in fH. SwissProt accession numbers for protein sequences are Q03591 (CFHR1) and P08603 (fH). Nucleotide numbering is based on the translation start site: A in ATG is +1.