Lymphoplasmacytic Lymphoma

By one report, approximately 50% of lymphoplasmacytic lymphomas (LPLs) carry the t(9;14)(p13;q32) translocation, in which PAX5 on 9p13 is juxtaposed with the constant switch (||) region of the IGH locus on 14q32.9 However, other investigators have not confirmed this observation. The translocation purportedly results in dys-regulation and overexpression of a normal PAX5 protein, a crucial regulatory protein in normal B-cell differentiation. PAX5 encodes a B-cell-specific transcription factor known as B-cell-specific activator protein (BSAP), thought to regulate B-cell genes such as CD19 and IGH. PAX5 also is thought to stimulate B-cell proliferation and transcrip-tionally repress TP53 in vitro. Breakpoints involved in the PAX5/IGH translocation are widely dispersed, making it difficult to design PCR assays that will detect many translocations, so detection is by FISH, reverse transcription-polymerase chain reaction (RT-PCR), or karyotyping.

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