Complotypes in pemphigus vulgaris: differences between Jewish and non-Jewish patients.

Haplotypes of alleles of the major histocompatibility complex (MHC) complement genes BF, C2, C4A, and C4B are inherited as single highly polymorphic genetic units called complotypes. There are about a dozen complotypes with frequencies above about 0.01 in Caucasians. In the blistering disease pemphigus vulgaris, the complotypes SC21 and SB45 were found to be markedly elevated in patients compared with general Caucasian controls. The SC21 increase was in Ashkenazi Jewish patients exclusively (relative risk = 17 in that population), whereas SB45 was found solely in non-Jewish Caucasians (specific population relative risk = 57). Although these are unusually high relative risks, it is most unlikely that these complotypes represent susceptibility genes for pemphigus vulgaris. Rather, it is probable that they mark extended major histocompatibility complex haplotypes with fixed DNA so that independent examples in the population have the same alleles. It is likely that it is the class II genes on these haplotypes that confer susceptibility.