New types of multiple and single gene deletions in the humanIgCH locus

Abstract
The locus for human immunoglobulin heavy chain constant region genes (IgCH) is characterized by a significant frequency of deleted or duplicated haplotypes, due to unequal crossing-over events. Four types of deletions and one duplication have been reported so far. We describe here a molecular study of four cases of IgCH deletions. Two of the three types of deletions are reported here for the first time. Analysis of genetic markers associated with the deleted haplotypes pointed to the independent origin of similar deletions and the involvement of intergenic sequences in the mispairing-recombination process. The reduced or absent transcription of theC γ 4 gene in twoC γ 2-deleted haplotypes offers an insight into the requirements for the isotype switch mechanism.