Translocation t(11,18)(q21;q21) is a characteristic genetic marker of the MALT lymphomas. The consequence of this translocation is the fusion of genes API2 and MALT1. Proteins API2 and MALT1 are normally quickly degraded but their chimeric transcript API1-MALT1 remains stable. Overexpression of API2-MALT1 continuously stimulates the transcription factor NF?B, which was described as a candidate proto-oncogene in a number of lymphomas.
Translocation t(11,18) is present in more than one third of the gastric MALT lymphomas. Cases with the translocation have a higher tendency to relapse (about 75 % of recurrent MALT lymphoma carry the translocation). Translocation in MALT lymphomas may occur also in another location than in the stomach, e.g. pulmonary localization has been proven in more than a half of cases, and only in a small amount in the salivary glands.
Translocation t(11,18) can be detected in various ways. The first option is to prove the presence of the fusion transcript API2-MALT1 by RT-PCR. The second possibility is the detection of translocation by FISH. In our laboratory we perform the interphase FISH with a commercially available "break apart" probe LSI® MALT1 (18q21) Dual Color, Break Apart Rearrangement Probe (Vysis/Abbott). The result of hybridization with this probe in a normal nucleus is the presence of two fused (yellow) signals indicating two intact copies of the MALT1 gene. In the abnormal cell with translocation involving 18q21 region we can observe one fused, one green and one red signal.
When FISH, we detect the break of the gene MALT1 using MALT1 Dual Color, Break Apart Rearrangement Probe, Vysis/Abbott (this probe does not identify a specific translocation partner). In a sample positive for rearrangement of the gene MALT1 we observe one yellow, one red and one green signal. In a negative sample we observe two yellow signals (fig. 1) . (dual color filter)
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