Long PCR detection of the C4A null allele in B8-C4AQ0-C4B1-DR3

The genes coding for the two components of complement 4 (C4), C4A and C4B, are located within the major histocompatibility complex (MHC) on the short arm of chromosome 6. Several studies have shown that deficiency of C4A is a ssociated with systemic lupus erythematosus (SLE), rheumatoid arthritis and scleroderma. A large deletion covering most of the C4A gene and the 21-hyd roxylase-A (21-OHA) pseudogene found on the extended haplotype B8-C4AQ0-C4B 1-DR3 is estimated to account for approximately two-thirds of C4A deficienc y in Caucasian SLE patients. Detection of this C4A null allele has been tec hnically difficult due to the high degree of homology between C4A and C4B, with protein analysis and restriction fragment length polymorphism (RFLP) a nalysis using Southern blotting being the only approaches available. In thi s study, a long PCR strategy was used to rapidly genotype for the C4A delet ion through specific primer design. The methodology makes use of the unique sequence of the G11 gene upstream of C4A and the sequence of a 6.4 kb retr otransposon, the human endogenous retrovirus HERV-K(C4), which is present i n intron 9 of C4A but absent in the case of the deletion. (C) 2000 Elsevier Science B.V. All rights reserved.