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Figure 3: Case 4: B-cell-specific polymerase chain reaction using primers directed at the framework 256 (FR256) regions of the immunoglobulin heavy-chain gene (IgH). The top arrow represents the internal control that is used to ensure the presence of amplifiable DNAin each sample. The bracket in the FR256 figure denotes the size range in which IgH gene products can be seen. Although the DNA is degraded and the signal is weak, patient B (case 4) clearly shows the presence of a clonally rearranged IgH gene using the FR256 primers. Clonal rearrangements of IgH genes were also noted in cases 1 and 2 (not shown in figure). Lanes A and C are from cases unrelated to this paper. Reproduced from [4] with permission of the Editor-in-Chief of Archives of Pathology and Laboratory Medicine on behalf of the editorial team of the journal and the American Association of Pathology.