Paired multiplex reverse-transcriptase polymerase chain reaction (PMRT-PCR) analysis as a rapid and accurate diagnostic tool for the detection of MLL fusion genes in hematologic malignancies

Outcomes of acute myeloid leukemia with KMT2A (MLL) rearrangement: a multicenter study of TROPHY group

Acute myeloid leukemia (AML) with KMT2A rearrangement (KMT2A-r) is associated with poor prognosis, but the benefit of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for KMT2A-r AML is unclear. We reviewed adult AML patients treated within the TROPHY group and identified 292 cases of KMT2A-r AML, 254 (87.0%) of whom achieved first complete remission (CR1) and 192 (75.6%) of CR1 patients underwent allo-HSCT. We show that allo-HSCT is an independent favorable prognostic factor in CR1 patients for both overall survival (OS) (hazard ratio [HR] = 0.56, 95% confidence interval [CI]: 0.45-0.69, P < 0.001) and cumulative incidence of relapse (CIR) (HR = 0.01, 95% CI: 0.005-0.04, P < 0.001). Among allo-HSCT recipients, survival outcomes were comparable between patients with KMT2A::MLLT3 and those with other 11q23/KMT2A rearrangements (3-year OS: 74.3% vs. 77.5%, P = 0.97; 3-year event-free survival [EFS]: 55.2% vs. 62.2%, P = 0.34; 3-year CIR: 24.4% vs. 20.8%, P = 0.32). Both multiparameter flow cytometry-based measurable residual disease (MFC-MRD) and KMT2A-r MRD determined by quantitative PCR prior to allo-HSCT were associated with worse transplant outcomes. Multivariable analysis identified detectable KMT2A-r MRD at allo-HSCT as a significant risk factor for reduced EFS (HR = 2.46, 95% CI: 1.32-4.60, P = 0.005). These findings confirm the survival benefit of allo-HSCT in adult patients with KMT2A-r AML and underscore the prognostic value of KMT2A-r MRD prior to transplantation.

The clinical observation of none-promyelocytic AML patients inducted with idarubicin or daunorubicin included standard regimens: a tertiary care center experience

BACKGROUND

Few Chinese study compared the impacts of idarubicin and daunorubicin based "3+7" intensive chemotherapies on early and long-term outcomes of AML patients through exploring their real-world data.

PATIENTS AND METHODS

Our none promyelocytic AML patients inducted with "3+7" regimens were studied to find out the factors relating with induction response and long term survival.

RESULTS

Idarubicin induction was related with less chemotherapy refractory rate comparing with daunorubicin induction (10% vs 25%, P = 0.02). But cytogenetic molecular risk classification was the only independent factor relating with achieving CR after initial induction or chemotherapy refractory (P = 0.000 and 0.036). Both to overall survival (OS) and progress free survival (PFS), having transplantation and chemotherapy refractory were independent factors related, MLL rearrangement and DNA methylating related genes' mutations as well. CR at time of transplantation and MLL rearrangement were independent factors relating both with OS after transplantation and relapse free survival after transplantation.

CONCLUSION

Traditional "3+7" chemotherapy regimen with idarubicin plays better in CR induction than that with daunorubicin. But the patient's long-term survival related with clinical practice aspects, like having stem cell transplantation, as well as genetic alterations equally, like MLL rearrangement and DNA methylating related genes' mutations.

Characterization of Common Chromosomal Translocations and Their Frequencies in Acute Myeloid Leukemia Patients of Northwest Iran

Objective

Detection of chromosomal translocations has an important role in diagnosis and treatment of hematological disorders. We aimed to evaluate the 46 new cases of de novo acute myeloid leukemia (AML) patients for common translocations and to assess the effect of geographic and ethnic differences on their frequencies.

Materials and Methods

In this descriptive study, reverse transcriptase-polymerase chain reaction (RT-PCR) was used on 46 fresh bone marrow or peripheral blood samples to detect translocations t (8; 21), t (15; 17), t (9; 11) and inv (16). Patients were classified using the French-American-British (FAB) criteria in to eight sub-groups (M0-M7). Immunophenotyping and biochemical test results of patients were compared with RT-PCR results.

Results

Our patients were relatively young with a mean age of 44 years. AML was relatively predominant in female patients (54.3%) and most of patients belonged to AML-M2. Translocation t (8; 21) had the highest frequency (13%) and t (15; 17) with 2.7% incidence was the second most frequent. CD19 as an immunophenotypic marker was at a relatively high frequency (50%) in cases with t (8; 21), and patients with this translocation had a specific immunophenotypic pattern of complete expression of CD45, CD38, CD34, CD33 and HLA-DR.

Conclusion

Similarities and differences of results in Iran with different parts of the world can be explained with ethnic and geographic factors in characterizations of AML. Recognition of these factors especially in other comprehensive studies may aid better diagnosis and management of this disease.

Single Fluorescence Channel-based Multiplex Detection of Avian Influenza Virus by Quantitative PCR with Intercalating Dye

Since its invention in 1985 the polymerase chain reaction (PCR) has become a well-established method for amplification and detection of segments of double-stranded DNA. Incorporation of fluorogenic probe or DNA intercalating dyes (such as SYBR Green) into the PCR mixture allowed real-time reaction monitoring and extraction of quantitative information (qPCR). Probes with different excitation spectra enable multiplex qPCR of several DNA segments using multi-channel optical detection systems. Here we show multiplex qPCR using an economical EvaGreen-based system with single optical channel detection. Previously reported non quantitative multiplex real-time PCR techniques based on intercalating dyes were conducted once the PCR is completed by performing melting curve analysis (MCA). The technique presented in this paper is both qualitative and quantitative as it provides information about the presence of multiple DNA strands as well as the number of starting copies in the tested sample. Besides important internal control, multiplex qPCR also allows detecting concentrations of more than one DNA strand within the same sample. Detection of the avian influenza virus H7N9 by PCR is a well established method. Multiplex qPCR greatly enhances its specificity as it is capable of distinguishing both haemagglutinin (HA) and neuraminidase (NA) genes as well as their ratio.

Rare MLL-ELL fusion transcripts in childhood acute myeloid leukemia-association with young age and myeloid sarcomas?

BACKGROUND

The chromosomal translocation t(11;19)(q23;p13) with a breakpoint within subband 19p13.1 is found mainly in acute myeloid leukemia (AML) and results in the MLL-ELL fusion gene. Variations in the structure of MLL-ELL seem to influence the leukemogenic potency of the fusion in vivo and may lie behind differences in clinical features. The number of cases reported so far is very limited and the addition of more information about MLL-ELL variants is essential if the possible clinical significance of rare fusions is to be determined.

CASE PRESENTATION

Cytogenetic and molecular genetic analyses were done on the bone marrow cells of a 20-month-old boy with an unusual form of myelomonocytic AML with multiple myeloid sarcomas infiltrating bone and soft tissues. The G-banding analysis together with FISH yielded the karyotype 47,XY, +6,t(8;19;11)(q24;p13;q23). FISH analysis also demonstrated that MLL was split. RNA-sequencing showed that the translocation had generated an MLL-ELL chimera in which exon 9 of MLL (nt 4241 in sequence with accession number NM_005933.3) was fused to exon 6 of ELL (nt 817 in sequence with accession number NM_006532.3). RT-PCR together with Sanger sequencing verified the presence of the above-mentioned fusion transcript.

CONCLUSIONS

Based on our findings and information on a few previously reported patients, we speculate that young age, myelomonoblastic AML, and the presence of extramedullary disease may be typical of children with rare MLL-ELL fusion transcripts.

Evidence-based RT-PCR methods for the detection of the 8 most common MLL aberrations in acute leukemias

MLL aberrations are detected in around 5-10% of acute myeloid and lymphatic leukemias and an additional 5% of acute myeloid leukemias show a partial internal MLL duplication (PTD). MLL rearrangements are important for therapy stratification, assessment of minimal residual disease and for targeted therapies. However, no truly evidence-based RT-PCR methods for the detection of most of these aberrations have been published yet. Based on the large data collection of MLL genomic breakpoints in acute leukemias comprising more than 1.600 cases at the Diagnostic Center for Acute Leukemias (DCAL) in Frankfurt, Germany that provide an overview over the experimentally observed fusion transcript variants, we developed RT-PCR methods for the reliable detection of the 8 most common MLL aberrations (MLL-AF4, MLL-AF6, MLL-AF9, MLL-AF10, MLL-ENL, MLL-ELL, MLL-EPS15, MLL PTD), together accounting for around 90% of MLL-r cases. The easily implementable RT-PCRs should enable a reliable detection of these MLL fusion transcripts by RT-PCR.

Targeted next-generation sequencing at copy-number breakpoints for personalized analysis of rearranged ends in solid tumors

BACKGROUND

The concept of the utilization of rearranged ends for development of personalized biomarkers has attracted much attention owing to its clinical applicability. Although targeted next-generation sequencing (NGS) for recurrent rearrangements has been successful in hematologic malignancies, its application to solid tumors is problematic due to the paucity of recurrent translocations. However, copy-number breakpoints (CNBs), which are abundant in solid tumors, can be utilized for identification of rearranged ends.

METHOD

As a proof of concept, we performed targeted next-generation sequencing at copy-number breakpoints (TNGS-CNB) in nine colon cancer cases including seven primary cancers and two cell lines, COLO205 and SW620. For deduction of CNBs, we developed a novel competitive single-nucleotide polymorphism (cSNP) microarray method entailing CNB-region refinement by competitor DNA.

RESULT

Using TNGS-CNB, 19 specific rearrangements out of 91 CNBs (20.9%) were identified, and two polymerase chain reaction (PCR)-amplifiable rearrangements were obtained in six cases (66.7%). And significantly, TNGS-CNB, with its high positive identification rate (82.6%) of PCR-amplifiable rearrangements at candidate sites (19/23), just from filtering of aligned sequences, requires little effort for validation.

CONCLUSION

Our results indicate that TNGS-CNB, with its utility for identification of rearrangements in solid tumors, can be successfully applied in the clinical laboratory for cancer-relapse and therapy-response monitoring.

Risk-based classification of leukemia by cytogenetic and multiplex molecular methods: results from a multicenter validation study

Modern management of leukemia and selection of optimal treatment approaches entails the analysis of multiple recurrent cytogenetic abnormalities with independent diagnostic or prognostic value. We report the first multicenter validation of a multiplex molecular assay for 12 relevant fusion transcripts relative to cytogenetic methods. Performance was evaluated using a set of 280 adult and pediatric acute or chronic leukemias representative of the variety of presentations and pre-analytical parameters encountered in the clinical setting. The positive, negative and overall agreements were >98.5% with high concordance at each of the four sites. Positive detection of cases with low blast count or at relapse was consistent with a method sensitivity of 1%. There was 98.7% qualitative agreement with independent reference molecular tests. Apparent false negatives corresponded to rare alternative splicing isoforms not included in the panel. We further demonstrate that clinical sensitivity can be increased by adding those rare variants and other relevant transcripts or submicroscopic abnormalities. We conclude that multiplex RT-PCR followed by liquid bead array detection is a rapid and flexible method attuned to the clinical laboratory workflow, complementing standard cytogenetic methods and generating additional information valuable for the accurate diagnosis, prognosis and subsequent molecular monitoring of leukemia.

Identification of MLL partner genes in 27 patients with acute leukemia from a single cytogenetic laboratory

Chromosomal rearrangements involving the MLL gene have been associated with many different types of hematological malignancies. Fluorescent in situ hybridization with a panel of probes coupled with long distance inverse-PCR was used to identify chromosomal rearrangements involving the MLL gene. Between 1995 and 2010, 27 patients with an acute leukemia were found to have a fusion gene involving MLL. All seven ALL patients with B cell acute lymphoblastic leukemia were characterized by the MLL/AFF1 fusion gene resulting from a translocation (5 patients) or an insertion (2 patients). In the 19 AML patients with acute myeloblastic leukemia, 31.6% of all characterized MLL fusion genes were MLL/MLLT3, 21.1% MLL/ELL, 10.5% MLL/MLLT6 and 10.5% MLL/EPS15. Two patients had rare or undescribed fusion genes, MLL/KIAA0284 and MLL/FLNA. Seven patients (26%) had a complex chromosomal rearrangement (three-way translocations, insertions, deletions) involving the MLL gene. Splicing fusion genes were found in three patients, leading to a MLL/EPS15 fusion in two and a MLL/ELL fusion in a third patient. This study showed that fusion involving the MLL gene can be generated through various chromosomal rearrangements such as translocations, insertions and deletions, some being complex or cryptic. A systematic approach should be used in all cases of acute leukemia starting with FISH analyses using a commercially available MLL split signal probe. Then, the analysis has to be completed, if necessary, by further molecular cytogenetic and genomic PCR methods.

Molecular findings in childhood leukemia in Brazil: high frequency of MLL-ENL Fusion/t(11;19) in infant leukemia

Translocations involving chromosome 11q23 are frequently found in pediatric leukemia, especially in infants. The mixed lineage leukemia (MLL)-AF4 fusion/t(4;11) is mostly found in acute lymphoblastic leukemia (ALL) and MLL-AF9 fusion/t(9;11) in acute myeloid leukemia (AML). We study 441 consecutive new cases of childhood leukemia diagnosed in Brazil. Chromosomal translocation was determined solely by conventional polymerase chain reaction (PCR) in 72 out of 265 ALL and in 43 out of 103 AML. MLL-AF4 fusion/t(4;11) was detected in 3 out of 265 ALL and MLL-AF9 fusion/t(9;11) in 4 out of 103 of AML. MLL-rearrangements were presented in 7 out of 23 infant leukemia, whose 5 were MLL-ENL fusion/t(11;19). No fusion MLL-AF4 fusion/t(4;11) was found. Other translocation frequencies differed from that reported for an American population suggesting interethnic differences on chromosomal translocations frequencies in acute leukemia.

Clinical features and prognostic implications of TCF3-PBX1 and ETV6-RUNX1 in adult acute lymphoblastic leukemia

BACKGROUND

The t(9;22) and t(4;11) chromosomal translocations, which generate the BCR-ABL and MLL-AF4 fusion genes, define high-risk subtypes of acute lymphoblastic leukemia in adults. However, the prognostic impact of other rarer fusion genes is less well established in adult acute lymphoblastic leukemia than in the childhood form.

DESIGN AND METHODS

In the context of the German Multicenter Therapy Study Group for Adult Acute Lymphoblastic Leukemia (GMALL) we used reverse transcriptase polymerase chain reaction to investigate 441 cases of BCR-ABL- and MLL-AF4-negative B-precursor acute lymphoblastic leukemia for the TCF3-PBX1 (E2A-PBX1) and ETV6-RUNX1 (TEL-AML1) fusion transcripts generated by the t(1;19)(q23;p13.3) and t(12;21)(p13;q22) translocations. Both are well-known molecular alterations in pediatric acute lymphoblastic leukemia in which they have favorable prognostic implications.

RESULTS

We identified 23 adult patients with TCF3-PBX1 and ten with ETV6-RUNX1. In contrast to previous reports we found no significant difference in overall survival between TCF3-PBX1-positive and -negative patients. At 2 years after diagnosis all the ETV6-RUNX1-positive patients were alive and in continuous complete remission, but their long-term outcome was negatively affected by late relapses. TCF3-PBX1-positive patients exhibited a characteristic CD34(-)/CD33(-) and mostly cyIg(+) immunophenotype. ETV6-RUNX1 only occurred in patients under 35 years old and was associated with a significantly lower white blood count.

CONCLUSIONS

In contrast to previous suggestions, adult patients with TCF3-PBX1-positive acute lymphoblastic leukemia do not appear to have a worse outcome than their negative counterparts. ETV6-RUNX1-positive patients had a very favorable performance status during the first few years but their long-term survival was negatively affected by late relapses. Both groups of patients are characterized by distinct clinicobiological features which facilitate their diagnostic identification.

Occurrence of Acute Myeloid Leukemia in Young Pregnant Women

Although acute leukaemia is rare in pregnancy its importance lies in its life-threatening potential, both to the child and the mother. The possibility of vertical transmission of leukemic cells increases the attention devoted to these patients and their offspring. Three cases of pregnant young women (15-17 years of age) with AML are presented. This series of cases is the first report where gene abnormalities such as ITD mutations of the FLT3 gene and AML1/ETO fusion genes were screened in pregnant AML patients and their babies, so far. Unfortunately, very poor outcomes have been associated to similar cases described in literature, and the same was true to the patients described herein. Although very speculative, we think that the timing and possible similar exposures would be involved in all cases.

A novel AF9 breakpoint in MLL-AF9-positive acute monoblastic leukemia

MLL-AF9 is the most frequent MLL rearrangement in childhood acute myeloid leukemia (AML) and it may be also found in acute lymphoblastic leukemia (ALL) of patients younger than 1-year-old (infants). We report a novel AF9 breakpoint site, located between previously reported sites A and B, detected in an infant who was diagnosed with AML-FAB M5. The occurrence of this new breakpoint should be considered when designing RT-PCR assays for the screening of MLL abnormalities. The precise characterization of the MLL-AF9 transcript is important to carry out the minimal residual disease analysis during the follow-up of the patients.

Complex MLL rearrangements in t(4;11) leukemia patients with absent AF4 · MLL fusion allele

The human mixed lineage leukemia (MLL) gene is frequently involved in genetic rearrangements with more than 55 different translocation partner genes, all associated with acute leukemia. Reciprocal chromosomal translocations generate two MLL fusion alleles, where 5'- and 3'-portions of MLL are fused to gene segments of given fusion partners. In case of t(4;11) patients, about 80% of all patients exhibit both reciprocal fusion alleles, MLL.AF4 and AF4.MLL, respectively. By contrast, 20% of all t(4;11) patients seem to encode only the MLL.AF4 fusion allele. Here, we analyzed these 'MLL.AF4(+)/AF4.MLL(-)' patients at the genomic DNA level to unravel their genetic situation. Cryptic translocations and three-way translocations were found in this group of t(4;11) patients. Reciprocal MLL fusions with novel translocation partner genes, for example NF-KB1 and RABGAP1L, were identified and actively transcribed in leukemic cells. In other patients, the reciprocal 3'-MLL gene segment was fused out-of-frame to PBX1, ELF2, DSCAML1 and FXYD6. The latter rearrangements caused haploinsufficiency of genes that are normally expressed in hematopoietic cells. Finally, patients were identified that encode only solitary 3'-MLL gene segments on the reciprocal allele. Based on these data, we propose that all t(4;11) patients exhibit reciprocal MLL alleles, but due to the individual recombination events, provide different pathological disease mechanisms.

Molecular cytogenetic findings of acute leukemia included in the Brazilian Collaborative Study Group of Infant acute leukemia

BACKGROUND

Chromosome abnormalities often occur prenatally in childhood leukemia, characterizing an early event in leukemogenesis. The majority of the abnormalities occurring in infants involve the MLL gene on chromosome band 11q23. We describe the molecular cytogenetic findings of 207 infant acute leukemia (IAL) cases included in the Brazilian Collaborative Study Group of Infant acute leukemia.

PROCEDURE

The diagnosis of Acute Lymphoblastic leukemia (ALL) or acute myeloblastic leukemia (AML) was made according to morphology and immunophenotyping classification, followed by conventional karyotyping. Samples were then screened using RT-PCR for the presence of specific chromosome translocations. FISH assay for MLL rearrangements was performed only in cases with negative or inconclusive cytogenetic or PCR results.

RESULTS

The characteristics of children with IAL were as follows: 115 boys and 92 girls, age range 0-23 months, mean age 12 months, 145 ALL, and 62 AML. A statistically significant association was observed between pro-B ALL cases and MLL+ve (P=0.0001) cases and the age group 0-3 months with MLL+ve (P=0.008) cases. Two rare cases of pro-T ALL with MLL+ve were found. Other than MLL rearrangements, various other molecular aberrations were detected including TEL/AML1+ve (n=9), E2A/PBX1+ve (n=4), PML/RARA+ve (n=4), and AML1/ETO+ve (n=2). Cytogenetic analysis revealed hyperdiploidy (n=6), del(7) in two cases and del(11)(q23) in seven cases.

CONCLUSIONS

Our results show that not only MLL rearrangements, but also other molecular abnormalities occur before birth and may contribute to leukemogenesis.

Acute lymphoblastic leukemia with 4;11 translocation analyzed by a multi-modal strategy of conventional cytogenetics, FISH, morphology, flow cytometry and molecular genetics, and review of the literature

We report a case of acute lymphoblastic leukemia (ALL) with a 4;11 translocation. Metaphase cells and interphase nuclei derived from a routine unstimulated culture of bone marrow were analyzed using a combined strategy of G-banding and fluorescent in situ hybridization (FISH) in addition to hematopathological analysis, flow cytometry, and molecular genetics. This multimodal approach enables a successful correlation of pathology and cytogenetics to support a comprehensive diagnosis of the patient. Meaningful prognostication and appropriate therapeutic considerations are possible only when accurate diagnostic information is given. We further search and review the literature for the most up-to-date information currently available for this subtype of ALL in the constantly evolving field of molecular cytogenetics.

Monitoring minimal residual disease by quantification of genomic chromosomal breakpoint sequences in acute leukemias with MLL aberrations

An estimated 10% of acute leukemias carry mixed-lineage leukemia (MLL) fusion genes. Approximately 50 different fusion partners of the MLL gene have already been molecularly identified. These leukemias are commonly regarded as high-risk cases and are treated accordingly with intensified therapy regimens, including hematopoietic stem cell transplantation. However, a subset of patients may achieve long-term remissions with conventional therapy. Monitoring minimal residual disease (MRD) is undoubtedly of great value in clinical decision making, also in the pre- and post-transplant setting. Here, we describe a novel method for detecting MRD in leukemias with MLL aberrations. The method is based on monitoring patient-specific chromosomal breakpoint DNA sequences. This has several advantages over other methods that are based either on detecting specific RNA molecules of MLL fusion genes or on surrogate markers. An accurate and absolute quantification of the MRD level is possible. No reference to housekeeping genes is necessary and the target structure is much more stable than any mRNA fusion transcript.

Cryptic MLL-AF10 fusion caused by insertion of duplicated 5′ part of MLL into 10p12 in acute leukemia: a case report

Chromosomal translocations involving the mixed lineage leukemia gene (MLL) located at 11q23 belong to common chromosomal abnormalities in both acute lymphoblastic (ALL) and acute myeloid leukemias (AML). It has been suggested that the mechanism of MLL leukemogenesis might be a result of a gain-of-function effect of the MLL fusion gene and simultaneous loss of function of one of the MLL alleles (haploinsufficiency). One of the recurrent translocations in AML-M5 involves chromosomal locus 10p12 and results in the MLL-AF10 fusion gene. Several mechanisms leading to MLL-AF10 fusion have been reported, and they have involved rearrangement of the 11q23 region. We present a detailed structural analysis of an AML case with an extra copy of the 5' part of MLL region and its insertion into the short arm of chromosome 10, resulting in an MLL-AF10 fusion without rearrangement of the MLL alleles on both chromosomes 11. Our observation supports a role for a simple MLL gain-of-function in leukemogenesis.

Molecular genetic analysis of haematological malignancies: I. Acute leukaemias and myeloproliferative disorders

Molecular genetic techniques are now routinely applied to haematological malignancies within a clinical laboratory setting. The detection of genetic rearrangements not only assists with diagnosis and treatment decisions, but also adds important prognostic information. In addition, genetic rearrangements associated with leukaemia can be used as molecular markers allowing the detection of low levels of residual disease. This review will concentrate on the application of molecular genetic techniques to the acute leukaemias and myeloprolferative disorders.

Classification of pediatric acute lymphoblastic leukemia by gene expression profiling

Contemporary treatment of pediatric acute lymphoblastic leukemia (ALL) requires the assignment of patients to specific risk groups. We have recently demonstrated that expression profiling of leukemic blasts can accurately identify the known prognostic subtypes of ALL, including T-cell lineage ALL (T-ALL), E2A-PBX1, TEL-AML1, MLL rearrangements, BCR-ABL, and hyperdiploid karyotypes with more than 50 chromosomes. As the next step toward developing this methodology into a frontline diagnostic tool, we have now analyzed leukemic blasts from 132 diagnostic samples using higher density oligonucleotide arrays that allow the interrogation of most of the identified genes in the human genome. Nearly 60% of the newly identified subtype discriminating genes are novel markers not identified in our previous study, and thus should provide new insights into the altered biology underlying these leukemias. Moreover, a proportion of the newly selected genes are highly ranked as class discriminators, and when incorporated into class-predicting algorithms resulted in an overall diagnostic accuracy of 97%. The performance of an array containing the identified discriminating genes should now be assessed in frontline clinical trials in order to determine the accuracy, practicality, and cost effectiveness of this methodology in the clinical setting.

Cryptic insertion and translocation or nondividing leukemic cells disclosed by FISH analysis in infant acute leukemia with discrepant molecular and cytogenetic findings

Of 51 infants with acute leukemia, 13 (25%) had contradictory findings on 11q23/MLL rearrangements that were analyzed by cytogenetic and Southern blot methods: seven had rearranged MLL and normal karyotype, four had rearranged MLL and abnormal karyotype with no 11q23 translocation, and two had germline MLL and 11q23 translocations. Fluorescent in situ hybridization (FISH) analysis using an MLL probe that was performed to elucidate the discrepancy disclosed the presence of normal dividing cells and nondividing leukemic cells in the same bone marrow in five patients, and cryptic insertion or translocation in another five. Subsequent FISH and reverse transcription-polymerase chain reaction analysis identified the MLL-AF10, MLL-AF4, or MLL-AF1q fusions that were produced by the cryptic rearrangements in four of the five patients. In the remaining three patients, the breakpoint of 11q23 translocation was located distal to the MLL locus in one, and the discrepancy was unresolved in two. Thus, FISH should complement cytogenetic analysis when cytogenetic and molecular genetic findings are contradictory in infant leukemia, and when infant leukemia does not show 11q23 translocations or other specific translocations including t(7;12), t(1;22), etc that are recurrently found in infant leukemia.