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The der(11)-encoded MLL/AF-4 fusion transcript is consistently detected in t(4;11)(q21;q23)-containing acute
J R Downing1, D R Head, S C Raimondi
1Department of Pathology, St Jude Children's Research Hospital, Memphis, TN 38105.
Insights
The common infant acute lymphoblastic leukemia (ALL) translocation t(4;11) involves MLL and AF-4 genes. Reverse transcription-polymerase chain reaction (RT-PCR) detects the MLL/AF-4 fusion transcript from the der(11) chromosome in all infant ALL cases, aiding diagnosis and monitoring.
Area of Science:
- Molecular Biology
- Hematology
- Genetics
Background:
- The t(4;11)(q21;q23) translocation is prevalent in infant acute lymphoblastic leukemias (ALLs).
- This translocation involves the MLL gene (chromosome 11) and the AF-4 gene (chromosome 4).
Purpose of the Study:
- To develop and validate reverse transcription-polymerase chain reaction (RT-PCR) assays for detecting t(4;11) fusion transcripts.
- To determine the origin and frequency of chimeric transcripts in pediatric ALL cases with t(4;11).
Main Methods:
- Oligonucleotide primers were designed based on MLL and AF-4 genes.
- RT-PCR assays were established to detect fusion transcripts from der(11) and der(4) chromosomes.
- Twenty-three pediatric ALL cases with t(4;11) were analyzed.
Main Results:
- The MLL/AF-4 fusion transcript from the der(11) chromosome was detected in all 23 cases (100%) with high sensitivity.
- Sequence analysis revealed alternative splicing of MLL/AF-4 fusion mRNAs.
- The der(4)-derived transcript was detected in only 84% of cases.
Conclusions:
- The der(11)-derived MLL/AF-4 fusion transcript is a critical factor in infant ALL pathogenesis.
- RT-PCR for the der(11)-encoded message is a valuable tool for diagnosing t(4;11) ALL and monitoring minimal residual disease.
Abstract:
The t(4;11)(q21;q23) is the most common translocation involving band 11q23 and is found predominantly in acute lymphoblastic leukemias (ALLs) of infants. Recent studies have shown that this translocation involves the MLL gene on chromosome 11 and the AF-4 gene on chromosome 4. Using oligonucleotide primers derived from these genes, we established reverse transcription-polymerase chain reaction (RT-PCR) assays for the detection of the fusion transcripts from both the der(11) and der(4) chromosomes. Using these assays we analyzed 23 pediatric cases of t(4;11) containing ALL. RT-PCR analysis for the der(11)-derived MLL/AF-4 fusion transcript resulted in its detection in every case at a sensitivity of greater than 1 leukemic cell in 10(5) cells. Sequence analysis of MLL/AF-4 PCR products demonstrated fusion mRNAs resulting from breaks in MLL introns 6, 7, or 8, with alternative splicing to one of three exons in the AF-4 gene. In contrast, analysis for the der(4)-derived transcript resulted in the detection of this chimeric mRNA in only 84% of the cases analyzed. These data suggest that the critical chimeric gene product involved in the establishment of the leukemic clone is derived from the der(11) chromosome. Moreover, these data demonstrate the utility of the RT-PCR assay for the der(11)-encoded message both for diagnosing t(4;11)-containing leukemia and for monitoring patients for minimal residual disease.