Polymorphism of the complement C8A and -B genes in two families with C8 beta deficiency and neisserial infections.

Serum samples from members of two Italian families with complement C8 beta deficiency were studied by SDS-PAGE under nonreducing conditions and by IEF. The proband of family I had suffered from two episodes of purulent meningitis and two of her uncles had suffered from only one episode, while the proband of family II had suffered from three different episodes. In contrast to previous findings, where C8 beta deficiency was cosegregating with C8A (alpha-gamma) allotype A, the proband of family II had the C8A allotype B. In addition, in one of her sons a novel variant of the C8 beta chain was detected. Studies at the DNA level in family I, using a recently described PCR system, demonstrate the presence of a C-T exchange, which creates a stop codon in exon 9 of the C8B gene, as cause for the C8 beta deficiency. The mutated allele does not carry the TaqI polymorphic restriction site located in intron 11 of the C8B gene. These findings provide evidence for multiple recombination events within the genetic region of the defective C8B gene.