Occasional BCLs have very complex rearrangements of IGH and other associated genes that may confound standard IGH PCR testing. This has been seen most frequently in FL, but similar genetic events undoubtedly occur with other IGH translocation partners. For example, most FLs have a single IGH/BCL2 rearrangement involving one chromosome 14 IGH allele, which is then unable to participate in a functional IGH rearrangement. An additional clonal rearrangement of the untranslocated IGH allele on the other chromosome 14 usually occurs and can be detected by IGH PCR. However, occasional FLs will have translocations of both IGH alleles to chromosome 18, resulting in the absence of a detectable clonal IGH rearrangement by PCR and often producing rearrangements of both the BCL2 M-bcr and m-bcr regions.
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