Importantly, although only 3 affected mice of 599 total recombinants were generated from the S1 and B6 crosses, all 3 of these mice were homozygous for Dysf mutant alleles and mutant alleles for Dysf and 2 of 3 were homozygous for mutant C5 alleles, with the third (i.e., one of the S1 F2 mice) being heterozygous for C5. This data, combined with the significant increase in rates of affected mice observed in SJ and D2 crosses, indicates the need for direct studies to understand the role for Dysf and/or C5 deficiency in EM/HD. Here, C5 is linked to erythema multiforme.