De novo Unbalanced 1;22 Translocation with 22q11 Deletion Syndrome

This report describes a newborn girl presenting with some of the common features of DiGeorge syndrome/velocardiofacial syndrome (DGS/VCFS), including hypocalcemia, atrial septal defect, and aortic stenosis. Several genetic tests were carried out to determine the origin of the clinical phenotype. MLPA was initially performed followed by aCGH, cytogenetic analysis, and FISH. Cytogenetic analysis of the proband's parents was also done. MLPA revealed a deletion in 22q11.1q11.2 spanning from the cat eye syndrome region to the most commonly deleted region in DGS/VCFS patients. The size of the deletion as defined by aCGH was 3.2 Mb. The karyotype of the proband was 45,XX,der(1)t(1;22)(p36.3;q11.2)dn,-22, the karyotypes of the parents were normal. FISH analysis showed that the 22q11 deletion occurred in the der(1). No loss or gain of chromosomal material was evident for chromosome 1, as confirmed by MLPA, aCGH, and FISH. Unbalanced translocations resulting in DGS are relatively rare, with limited reports in the literature. To our knowledge, this is the second case involving chromosome 1 and the first one with breakpoints in 1p36 and 22q11.2. This case also emphasizes the importance of combining diagnostic methods to better understand a given genetic abnormality.

Chronic neutrophilic leukemia with congenital Robertsonian translocation successfully treated with allogeneic bone marrow transplantation in a young man

We present a 23-year-old man with chronic neutrophilic leukemia (CNL). Physical examination revealed hepatosplenomegaly. Leukocytosis was evident with predominance of mature neutrophils with basophilic granules. Bone marrow aspiration revealed mature myeloid hyperplasia. Congenital Robertsonian translocation [45,XY,der(13;22)(q10;q10), in all of analyzed 20 cells] was detected; however, cytogenetic and molecular studies for 9:22 translocation were negative. He was diagnosed with CNL and hydroxyurea was started to control his symptoms and white blood cell count. He was then successfully treated with allogeneic bone marrow transplantation (BMT). Although the prognosis of CNL was not determined, curative therapy including allogeneic hematopoietic stem cell transplantation should be attempted in young patients with CNL.

Dermatofibrosarcoma protuberans

Dermatofibrosarcoma protuberans (DFSP) is a soft tissue neoplasm of intermediate malignancy that is initially localized to the skin from where it can invade deep structures (fat, fascia, muscle and bone). It is the most frequent fibrohistiocytic tumor, comprising approximately 1.8 % of all soft tissue sarcomas and 0.1 % of all cancers. It has an estimated incidence of 0.8-5 cases per one million persons per year. Treatment of localized disease consists in complete surgical excision of the lesion by conventional surgery with wide margins (>3 cm) or by micrographic Mohs surgery. Although the cases of metastatic DFSP do not reach 5 % of the total, almost all of them appear after previous local relapses. The prognosis for metastatic cases is very poor with a survival of less than 2 years following detection of metastatic disease. Patients with locally advanced DFSP are not candidates for an initial radical surgical therapy therefore neoadyuvant treatment is required prior to surgery in order to reduce tumor burden. In this regard, chemotherapy and radiotherapy have not been highly efficacious so it is necessary to consider new alternatives. The demonstration of the oncogenic power of the translocation COL1A1-PDGFB in DFSP has allowed the successful introduction of drug therapy with antagonists of the PDGFB receptor for metastatic or locally advanced cases.

Distinct patterns of histone methylation and acetylation in human interphase nuclei

To study 3D nuclear distributions of epigenetic histone modifications such as H3(K9) acetylation, H3(K4) dimethylation, H3(K9) dimethylation, and H3(K27) trimethylation, and of histone methyltransferase Suv39H1, we used advanced image analysis methods, combined with Nipkow disk confocal microscopy. Total fluorescence intensity and distributions of fluorescently labelled proteins were analyzed in formaldehyde-fixed interphase nuclei. Our data showed reduced fluorescent signals of H3(K9) acetylation and H3(K4) dimethylation (di-me) at the nuclear periphery, while di-meH3(K9) was also abundant in chromatin regions closely associated with the nuclear envelope. Little overlapping (intermingling) was observed for di-meH3(K4) and H3(K27) trimethylation (tri-me), and for di-meH3(K9) and Suv39H1. The histone modifications studied were absent in the nucleolar compartment with the exception of H3(K9) dimethylation that was closely associated with perinucleolar regions which are formed by centromeres of acrocentric chromosomes. Using immunocytochemistry, no di-meH3(K4) but only dense di-meH3(K9) was found for the human acrocentric chromosomes 14 and 22. The active X chromosome was observed to be partially acetylated, while the inactive X was more condensed, located in a very peripheral part of the interphase nuclei, and lacked H3(K9) acetylation. Our results confirmed specific interphase patterns of histone modifications within the interphase nuclei as well as within their chromosome territories.

Interleukin-2 receptor beta chain locus rearrangement in a T-cell acute lymphoblastic leukemia

A translocation t(1;22)(p13;q13) was detected in a child with T-cell acute lymphoblastic leukemia (T-ALL). FISH studies showed that the breakpoint was located in the 5' part of the interleukin-2 receptor beta chain (IL2RB) locus, but could only be located distal to 1p13.3 on the partner chromosome. This is the first case of the IL2RB locus rearrangement in T-ALL. The localization of the breakpoint suggests that the chromosomal translocation results in deregulation of IL2RB expression.

Molecular cytogenetic characterization of deletions on der(9) in chronic myelocytic leukemia

The t(9;22)(q34;q11), generating the Philadelphia chromosome, is found in more than 90% of patients with chronic myelocytic leukemia (CML). Deletions adjacent to the translocation breakpoint on the derivative chromosome 9 have been described by several groups. These studies revealed two primary points: (1) genomic microdeletions were concomitant with the t(9;22) rearrangement; and (2) the location of the deleted sequence was centromeric to ABL and telomeric to BCR genes. We report on a detailed molecular cytogenetic characterization of chromosomal rearrangements in two CML patients bearing a complex variant t(9;22) and insertions of chromosome 22 sequences in 9q34. Our study shows that the location of the deleted sequences was downstream of the ABL gene and that genomic microdeletions were concomitant with the ins(9;22)(q34;q11q11) rearrangement.

Spinal epidural extraskeletal Ewing sarcoma in an adolescent boy: a case report

Extraskeletal Ewing sarcoma (EES) represents a rare soft tissue malignant neoplasm histologically similar to skeletal Ewing sarcoma. It occurs mainly in adolescents and young adults and commonly affects the paravertebral regions. The differential diagnosis includes other small, blue round cells tumors. The authors report a case of an EES involving the spinal epidural and paravertebral spaces in an adolescent boy. EES diagnosis was confirmed by features of histologic analysis and immunohistochemistry and by the presence of the t(11;22)(q24;q12) chromosomal translocation by reverse transcriptase-polymerase chain reaction.

A 200-kb region of human chromosome 22q11.2 confers antipsychotic-responsive behavioral abnormalities in mice

Human chromosome 22q11.2 has been implicated in various behavioral abnormalities, including schizophrenia and other neuropsychiatric/behavioral disorders. However, the specific genes within 22q11.2 that contribute to these disorders are still poorly understood. Here, we show that an approximately 200-kb segment of human 22q11.2 causes specific behavioral abnormalities in mice. Mice that overexpress an approximately 200-kb region of human 22q11.2, containing CDCrel, GP1Bbeta, TBX1, and WDR14, exhibited spontaneous sensitization of hyperactivity and a lack of habituation. These effects were ameliorated by antipsychotic drugs. The transgenic mice were also impaired in nesting behavior. Although Tbx1 has been shown to be responsible for many physical defects associated with 22q11.2 haploinsufficiency, Tbx1 heterozygous mice did not display these behavioral abnormalities. Our results show that the approximately 200-kb region of 22q11.2 contains a gene(s) responsible for behavioral abnormalities and suggest that distinct genetic components within 22q11.2 mediate physical and behavioral abnormalities.

Rational approaches to the design of therapeutics targeting molecular markers: the case of chronic myelogenous leukemia

Progress in understanding the molecular basis of signal transmission and transduction has contributed substantially to clarifying the mechanisms of leukemogenesis and of leukemia progression and has led to the identification of a number of specific molecular targets for treatment. Chronic myeloid leukemia (CML) has provided one of the best models, as the identification of a leukemia-specific hybrid tyrosine kinase (BCR-ABL, p210, p190) has led to the identification and the successful therapeutic application of a powerful tyrosine kinase inhibitor, imatinib. The BCR-ABL fusion gene is the result of a reciprocal translocation between the long arms of chromosomes 9 and 22, t(9;22)(q34;q11), which characterizes more than 95% of the cases of CML. The resulting chimeric proteins (P210 and P190), which retain a constitutively activated tyrosine kinase activity, have a causative role in the genesis of the leukemia process. In agreement with this observation, BCR-ABL tyrosine kinase inhibitors have recently emerged as powerful new therapeutic tools, obtaining extraordinary results in early chronic-phase CML as well as in more advanced phases of the disease. Although these results represent a remarkable breakthrough, there are still numerous issues, such as the emergence of resistance, that remain unsolved and that will need further investigation. In spite of its low incidence, CML remains a paradigmatic model for understanding the pathogenesis and therapeutic options of human leukemias.

Gene expression microarray analysis and genome databases facilitate the characterization of a chromosome 22 derived homogeneously staining region

Karyotype and fluorescence in situ hybridization (FISH) analyses previously identified a homogeneously staining region (HSR) derived from chromosome 22 in OV90, an epithelial ovarian cancer (EOC) cell line. Affymetrix expression microarrays in combination with the UniGene and Human Genome Browser databases were used to identify the candidate genes comprising the amplicon of the HSR, based on comparison of expression profiles of OV90, EOC cell lines lacking HSRs and primary cultures of normal ovarian surface epithelial (NOSE) cells. A group of probe sets displaying a minimum 3-fold overexpression with a high reliability score (P-call) in OV90 were identified which represented genes that mapped within a 1-2 Mb interval on chromosome 22. A large number of probe sets, some of which represent the same genes, displayed no evidence of overexpression and/or low reliability scores (A-call). An investigation of the probe set sequences with the Affymetrix and Sanger Institute Chromosome 22 Group databases revealed that some of the probe sets displaying discordant results for the same gene were complementary to intronic sequences and/or the antisense strand. Microarray results were validated by RT-PCR. Genomic analysis suggests that the HSR was derived from the amplification of a 1.1 Mb interval defined by the chromosomal map positions of ZNF74 and Hs.372662, at 22q11.21. The deduced amplicon is derived from a complex region of chromosome 22 that harbors low-copy repeats (LCRs). The amplicon contains 18 genes as likely targets for gene amplification. This study illustrates that large-scale expression microarray analysis in combination with genome databases is sufficient for deducing target genes associated with amplicons and stresses the importance of investigating probe set design before engaging in validation studies.

A new complex rearrangement involving the ETV6, LOC115548, and MN1 genes in a case of acute myeloid leukemia

A new complex rearrangement involving chromosome bands 5q13, 12p13, 22q11, and 3q12 was identified and characterized in a patient with acute myeloid leukemia. Fluorescence in situ hybridization showed the involvement of the ETV6 gene in 12p13. ETV6 primers were specifically designed for 3'- and 5'-RACE-PCR experiments, which led to the identification of the other two rearranged genes. The derivative chromosome 5 harbored a fusion of the ETV6 sequence with that of the LOC115548 gene. The two genes were placed in opposite orientation and did not encode a fusion protein. On the derivative chromosome 12, ETV6 was fused to the MN1 gene on chromosome 22. Also in this case, the insertion, within the MN1 sequence, of a portion of chromosome 3 prevented the formation of a fusion protein. Finally, the derivative chromosome 22 contained the 3' portions of both LOC115548 and MN1, and no fusion transcript with coding potential could be predicted. In conclusion, all chromosome breakpoints led to the truncation of the three involved genes in the absence of predicted fusion proteins. This study lends further support to the hypothesis that gene disruption resulting in either loss of function or haploinsufficiency may be relevant in acute myeloid leukemia pathogenesis.

Allelic variations at the haploid TBX1 locus do not influence the cardiac phenotype in cases of 22q11 microdeletion

Microdeletion at the 22q11 locus is characterised by a high clinical variability. Congenital heart defects (CHD) are the most life-threatening manifestations of the syndrome and affect approximately 50% of patients carrying the deleted chromosome 22. The causes of this phenotype variability remain unknown although several hypotheses have been raised. It has been suggested that allelic variations at the haploid locus could modify the phenotypic expression. Regarding this hypothesis, TBX1 was thought to be a major candidate to the cardiac phenotype or its severity in patients carrying the 22q11 microdeletion. A mutational screening was performed in this gene, in a series of 39 deleted patients, with and without CHD. The results indicate that mutations in TBX1 are not likely to be involved in the cardiac phenotype observed in del22q11 patients.

Molecular cytogenetic characterization of proximal-type epithelioid sarcoma

Proximal-type epithelioid sarcoma is a recently described soft-tissue tumor that is distinguished from conventional-type epithelioid sarcoma by a far more aggressive clinical course, frequent location in the proximal anatomic regions, and variable rhabdoid morphology. Because of their rarity and peculiar morphology, proximal-type epithelioid sarcomas frequently pose serious diagnostic dilemmas, being easily misdiagnosed as a variety of other malignant neoplasms. To date, the information available on the genetic alterations associated with this tumor entity has been confined to single conventional cytogenetic reports. In this article, we present the results of a conventional and molecular cytogenetic analysis of six proximal-type epithelioid sarcomas. Spectral karyotyping analysis of these cases deciphered the characteristics of several marker chromosomes and complex translocations, leading to the recognition of recurrent rearrangements. The most frequently involved chromosome arm was 22q, and the identification of two cases with a similar translocation, t(10;22), suggests a role for one or more genes on chromosome 22 in the pathogenesis of this tumor and provides an opportunity for finely mapping the translocation-associated breakpoints. Chromosome arm 8q gain was also a frequent event and correlated with gain of MYC gene copy number, as demonstrated by fluorescence in situ hybridization. A review of both cases reported in the literature and those presented in this study reinforced the involvement of chromosomes 8 and 22 and also indicated frequent rearrangements of chromosomes 7, 14, 18, and 20.

Coexistent Rearrangements of c-MYC,BCL2, andBCL6 Genes in a Diffuse Large B-Cell Lymphoma

We present a patient with stage III de novo diffuse large B-cell lymphoma. The lymphoma cells showed mature B-cell immunophenotype but lacked surface immunoglobulin (Ig) expression. Long-distance and long-distance inverse polymerase chain reaction assays to detect the oncogene/Ig gene rearrangement revealed that the cells carried 3 independent fusion genes, namely, c-MYC/Ig heavy chain gene (IgH), BCL2/IgH, and Ig lambda light chain gene/BCL6. Thus, the lymphoma cells concurrently carried t(8;14)(q24;q32), t(14;18)(q32;q21), and t(3;22)(q27;q11), which developed in association with class switching, V/D/J recombination, and somatic hypermutation, respectively. The lymphoma responded to chemoradiotherapy, and the patient has been well for 2 years, suggesting that multiple oncogene rearrangements may not necessarily be associated with poor clinical outcome.

Safety of live viral vaccines in patients with chromosome 22q11.2 deletion syndrome (DiGeorge syndrome/velocardiofacial syndrome)

The package inserts of live viral vaccines include immunodeficiency as a contraindication. Nevertheless, patients with mild forms of immunodeficiency may benefit from vaccination. No published guidelines exist for the administration of these vaccines specifically to patients with chromosome 22q11.2 deletion syndrome. This syndrome is also sometimes called DiGeorge syndrome and is associated with thymic hypoplasia and diminished T-cell numbers and has a wide spectrum of phenotypic features that include cardiac anomalies, dysmorphic facial features, and hypocalcemia. Patients generally exhibit a mild to moderate decrement in T-cell numbers with preservation of T-cell function. The aims of this study were to investigate the incidence of side effects after live viral vaccine administration in a population with chromosome 22q11.2 deletion syndrome. The high frequency of this syndrome in the population (1:3000 children) mandates a greater understanding of the risks and benefits related to live viral vaccine administration. A retrospective analysis of vaccine adverse events was performed. The data acquisition form evaluated the frequency of live vaccine administration and the consequences of both vaccination and withholding the vaccine. Flow cytometric enumeration of T cells was performed as part of an immunologic evaluation. Thirty-two of 59 responders were vaccinated with the varicella vaccine. Only 9% of patients reported adverse events. However, 63% of unvaccinated children developed chickenpox. Comparison of patients who tolerated the vaccine with those who reported adverse events showed no statistically significant differences in current age (7 vs 5.7 years), age at vaccination (3 vs 2.5 years), or T-cell subset counts: CD3 (1951 vs 2083 cells/ microL), CD4 (1283 vs 1463 cells/ microL), and CD8 (530 vs 502 cells/ microL). Fifty-two of 59 responders were vaccinated with measles-mumps-rubella (MMR). Twelve (23%) of 52 reported mild side effects, including fever, rash, and constitutional symptoms. No severe adverse reactions were reported. No patient reported natural disease with measles, mumps, or rubella. There were no statistically significant differences between the T-cell counts in the vaccinated group reporting side effects versus the vaccinated group without side effects (mean CD3 counts: 1928 vs 1736 cells/ microL; CD4 counts: 1250 vs 1127 cells/ microL; and CD8 counts: 528 vs 483 cells/ microL). In our study, patients with chromosome 22q11.2 deletion syndrome had a similar incidence of adverse effects with varicella and MMR vaccines compared with that reported in the general population. All side effects were mild. However, in patients who did not receive the varicella vaccine, an overwhelming 63% contracted the disease. Patients who were not vaccinated against MMR did not develop natural disease. The data suggest that this is a cohort of patients with 22q11.2 deletion syndrome who have tolerated live viral vaccinations without evidence of significant side effects. A prospective study could address whether there are T-cell thresholds below which vaccination is unsafe; however, the information that we present suggests that vaccinating children with chromosome 22q11.2 deletion with live viral vaccines does not carry a significantly higher risk of adverse reactions compared with the general population, provided that they have no evidence of severe immunocompromise.

No justification of routine screening for 22q11 deletions in patients with overt cleft palate

The velo-cardio-facial syndrome (VCFS), caused by a submicroscopic deletion of chromosome 22q11, is the most common syndrome that has palatal anomalies as a major feature. A possible strategy for early detection of VCFS is routine screening for 22q11 deletions in all infants with cleft palate (CP). The purpose of this study was to evaluate whether this strategy is preferable to testing on clinical suspicion. At the Nijmegen Cleft Palate Craniofacial Center, 58 new patients with overt CP were routinely tested, using fluorescence in situ hybridization (FISH), for a 22q11 deletion. One deletion was identified in a newborn girl with an overt CP who was clinically not suspected of having VCFS. Based on this study (n = 45) and the literature (n = 54), the prevalence of 22q11 deletions among children with CP, but without any other symptoms of VCFS, is estimated to be one in 99. We take the view that this figure is rather low and that early discovery will rarely have significant clinical or genetic consequences. Because CP patients remain under medical attention, almost all of the infants with isolated CP and VCFS will be recognized as having the syndrome at a later age when additional features have developed. Therefore, we conclude that routine FISH testing for 22q11 deletions in infants with overt CP is not indicated, provided clinical follow-up is guaranteed.

Five new subjects with ring chromosome 22

Ring chromosome 22, a rare cytogenetic finding, was first described by Weleber et al. in 1968. Since then approximately 50 patients have been reported in the medical literature. We describe five previously unreported subjects with ring chromosome 22 syndrome, summarize the clinical findings of reported patients from the literature and discuss the involvement of the ring chromosome and clinical outcome. Our subjects demonstrated the prominent features of this syndrome including mental retardation, hypotonia, motor delay, lack of speech, full eyebrows, and large ears. In addition, two of our subjects had central nervous system malformations and regression. The lack of consistent physical abnormalities in our subjects further supports no consistent phenotype manifestations in this cytogenetic syndrome. The variable clinical manifestations seen in ring chromosome 22 subjects may be associated with loss of chromosome 22 sequences near the telomere or attributed to the genetic background of each subject. Similarly, recessive alleles unmasked by the deletion could also contribute to the phenotype.

Clinical applications of BCR-ABL molecular testing in acute leukemia

Recent advances in molecular genetics impact the health care and outcome of patients with acute lymphoblastic leukemia (ALL). BCR-ABL, a common molecular defect in adult ALL, is a valuable tumor marker whose detection influences prognosis and clinical management decisions. Molecular methods such as fluorescence in situ hybridization (FISH), reverse-transcriptase polymerase chain reaction (rtPCR), and real-time quantitative rtPCR can be used to detect the chimeric BCR-ABL gene or its transcripts. These molecular assays improve our ability to measure residual disease and to estimate risk of relapse. On the horizon are gene expression profiles that will likely provide additional information beyond what is obtainable with current clinical and laboratory approaches.

Evans syndrome in a patient with chromosome 22q11.2 deletion syndrome: a case report

One patient with a chromosome 22q11.2 deletion and Evans syndrome is reported in this paper. Microdeletions of 22q11.2 are the main etiology for DiGeorge syndrome, a disorder characterized by heart defects, immune deficiencies due to aplasia or hypoplasia of the thymus, and hypocalcemia. Evans syndrome refers to a hematological autoimmune disorder with autoimmune hemolytic anemia accompanied by immune thrombocytopenia. A wide range of autoimmune disorders have been described in DiGeorge syndrome and velocardiofacial syndrome, including one prior report of autoimmune hemolytic anemia and immune thrombocytopenia. The patient reported herein strengthens the association between the 22q11.2 deletion spectrum and Evans syndrome.

A unique clone involving multiple structural chromosome rearrangements in a myelodysplastic syndrome case

In a young female patient presenting with a myelodysplastic syndrome (MDS), a unique clone involving six structural chromosome rearrangements was identified using G-banding and molecular cytogenetic techniques. Fifty GTG-banded metaphases from bone marrow were initially analyzed and all metaphases contained all of the six structural chromosome rearrangements. To further define the GTG-banded karyotype, a series of fluorescence in situ hybridization and primed in situ labeling experiments were performed and the karyotype was then characterized as: 46,XX,r(5)(p13q13),der(20)t(5;20),dup(11)(p11.2p15), r(11)(p15q25),del(13)(q14),idic(22)(p11). The patient quickly progressed to acute nonlymphocytic leukemia three months after the diagnosis and died of a hemorrhage in the brain parenchyma two months later. In this case, the multiple structural chromosome rearrangements conferred an obvious cellular proliferative advantage and indicated a very poor prognosis. Considering that multiple chromosome abnormalities associated with MDS transformation are often polyclonal, this unique clone involving six structural chromosome rearrangements make our case highly unusual.

Detection of a novel reciprocal t(16;22)(q11.2;q12) in a Ewing sarcoma

Several structural and numerical chromosomal abnormalities have been identified as primary and secondary chromosomal aberrations in Ewing sarcoma (ES). The majority of these are t(11;22) and trisomies, especially of chromosome 8. Specific chromosomal abnormalities often correlate with particular morphologic or phenotypic subtypes of tumor and play an important role in prognosis. The objective of this report is the cytogenetic evaluation of a case of ES using G-banding, fluorescence in situ hybridization, and spectral karyotyping techniques. Multiple chromosomal aberrations were identified including a novel reciprocal t(16;22)(q11.2;q12).

Newly established clear cell sarcoma (malignant melanoma of soft parts) cell line expressing melanoma-associated Melan-A antigen and overexpressing C-MYC oncogene

Clear cell sarcoma (CCS), malignant melanoma of soft parts, is a rare malignant tumor with a poor prognosis. In this study, a CCS cell line, designated MP-CCS-SY, was established from a metastatic tumor of a 17-year-old Japanese girl that originated in the left Achilles tendon. A small number of melanosomes were detected in the cytoplasm by electron microscopy. The melanosomes immunoreacted with two melanoma-associated antibodies, HMB45 and Melan-A. A Western blot demonstrated the existence of a Melan-A antigen in this cell line. Although a t(12;22)(q13;q12), which is characteristic of CCS, was not identified by a chromosomal analysis with conventional banding techniques, fluorescence in situ hybridization analysis with painting probes of chromosomes 12 and 22 revealed the insertion of a chromosome 12 fragment into one of the long arms of chromosome 22. The chimeric EWS/ATF1 transcript was detected by the reverse transcriptase polymerase chain reaction. Extra copies and structural abnormalities of chromosome 8 were observed. Overexpression of c-myc mRNA was detected by Northern blot analysis and may have a role in malignant progression of CCS. The availability of this MP-CCS-SY cell line will help to understand the molecular biology of this malignancy and should be useful as a tool for developing an immunotherapy.

Complex variant Philadelphia translocations involving the short arm of chromosome 6 in chronic myeloid leukemia

BACKGROUND AND OBJECTIVES

Around 5% of chronic myeloid leukemias (CML) are characterized by complex variant Philadelphia (Ph) translocations involving one or more chromosomal regions in addition to 9 and 22. The BCR/ABL1 fusion gene is usually found on der(22). The additional gene(s) involved in complex variant Ph rearrangements have not been characterized.

DESIGN AND METHODS

We performed fluorescent in situ hybridization (FISH) in three complex variant Ph translocations involving the short arm of chromosome 6 in addition to 9 and 22. The BCR/ABL1 D-FISH probe was applied to localize the BCR/ABL1 fusion gene as well as the 5'ABL1 and the 3'BCR. Locus-specific probes were used to narrow the 6p breakpoint.

RESULTS

In all cases the BCR/ABL1 fusion gene was located on the Ph chromosome whereas the reciprocal ABL1/BCR gene was detected only in patient #2. On 6p, breakpoints were narrowed to three different regions: centromeric to the human major histocompatibility complex (MHC), between PAC 524E15 and PAC162J16, in the first patient, and telomeric to the MHC, between PAC 329A5 and PAC 145H9, and between PAC 136B1 and PAC 206F19, in the second and third patients, respectively. In patients #2 and 3 a chromosomal rearrangement different from a true complex variant was discovered. In both cases, a classical t(9;22) was associated with an additional translocation involving the der(9)t(9;22).

INTERPRETATION AND CONCLUSIONS

Rearrangements at 6p in complex Ph aberrations involve more than one gene/locus. Classical t(9;22), masked by additional chromosomal rearrangements, can resemble complex variant Ph translocations, and can be detected only using appropriate FISH probes.

[Pseudohypoparathyroidism or hypoparathyroidism? A misleading clinical presentation]

We report the case of a 27-year old woman who presented hypocalcemia and hyperphosphoremia during her first pregnancy. Her phenotype was in favor of Albright's hereditary osteodystrophy: short stature, obesity, round face, brachymetacarpy and mental retardation. However, the diagnosis of pseudohypopara thyroidism type Ia was ruled out due to low PTH level (10 pg/ml). The patient's 22q11 microdeletion was suspected and identified because of the association of severe neonatal hypocalcemia, abnormal face and renal malformation in her children. Deletion 22q11 leads to various syndromes, including Di George syndrome, also referred to as CATCH 22 syndrome (Cardiac defect (C), Abnormal face (A), Thymic hypoplasia (T), Cleft palate (C) and Hypocalcemia (H)). Retrospectively, the patient presented with symptoms suggestive of CATCH 22: abnormal face, hypernasal voice suggestive of velopharyngeal insufficiency, mental retardation, recurrent otitis in childhood. It is also noteworthy that there was an idiopathic thrombocytopenic purpura. In conclusion, while the phenotype was suggestive of Albright's hereditary osteodystrophy, the constatation of a low PTH level would cast doubt on this diagnosis. Furthermore, the 22q11 microdeletion should be searched by FISH (Fluorescence In Situ Hybridization) in all patients with hypopara thyroidism of unknown origin, even in the absence of cardiac malformations. Finally, it seems that patients with CATCH 22 would be predisposed to auto-immune disease as a result of thymic dysfunction.

Statistical analysis of the DNA sequence of human chromosome 22

We study statistical patterns in the DNA sequence of human chromosome 22, the first completely sequenced human chromosome. We find that (i). the 33.4 x 10(6) nucleotide long human chromosome exhibits long-range power-law correlations over more than four orders of magnitude, (ii). the entropies H(n) of the frequency distribution of oligonucleotides of length n (n-mers) grow sublinearly with increasing n, indicating the presence of higher-order correlations for all of the studied lengths 1<or=n<or=10, and (iii). the generalized entropies H(n)(q) of n-mers decrease monotonically with increasing q and the decay of H(n)(q) with q becomes steeper with increasing n<or=10, indicating that the frequency distribution of oligonucleotides becomes increasingly nonuniform as the length n increases. We investigate to what degree known biological features may explain the observed statistical patterns. We find that (iv). the presence of interspersed repeats may cause the sublinear increase of H(n) with n, and that (v). the presence of monomeric tandem repeats as well as the suppression of CG dinucleotides may cause the observed decay of H(n)(q) with q.

Molecular determinants of neural crest migration

Normal septation of the cardiac outflow tract requires migration of neural crest cells from the posterior rhombencephalon to the branchial arches and developing conotruncal endocardial cushions. Proper migration of these cells is mediated by a variety of molecular cues. Adhesion molecules, such as integrins, are involved in the interaction of neural crest cells with the extracellular matrix, while cadherins allow neural crest cells to interact with each other during their migration. Pax3 appears to be important for proliferation of neural crest precursors, and connexin-43-mediated gap junction communication influences the rate of migration. Endothelin and its receptors are required for normal postmigratory differentiation. Platelet-derived growth factor and retinoic acid have roles in neural crest migration and differentiation as well. Finally, the similarity between the cardiovascular malformations seen in the DiGeorge and 22q11 deletion syndromes and animal models of neural crest deficiency has led to the examination of the role of genes located near or within the DiGeorge critical region in neural crest migration.

Immunophenotypic profile and FISH analysis in a case of Ewing's sarcoma

Ewing's sarcoma arising in the right fibula was diagnosed in a 12 years old female, considering clinical presentation, radiological findings and histological features. Our work points towards a possible neuroectodermal origin of Ewing's sarcoma, since MIC2/12E7 marker was found to be positive. Translocation t (11;22) (q24;q12) was found as the main cytogenetic change in this tumor, by means of FISH analysis.

Insertion (22;9)(q11;q34q21) in a patient with chronic myeloid leukemia characterized by fluorescence in situ hybridization

An unusual cytogenetic rearrangement, described as ins(22;9)(q11;q34q21), was detected in a 49-year-old male patient diagnosed with chronic myeloid leukemia (CML). Reverse transcriptase polymerase chain reaction (RT-PCR) revealed a b3a2 fusion transcript. In order to confirm the cytogenetic findings and fully characterize the inverted insertion, we performed fluorescence in situ hybridization (FISH) assays using locus-specific and whole chromosome painting probes. Our FISH analysis showed the presence of the BCR/ABL fusion gene, verified the insertion and determined that the breakpoint on chromosome 22 where the insertion took place was located proximal to the BCR gene and distal to the TUPLE1 gene on 22q11.

Molecular confirmation of Ewing sarcoma

OBJECTIVE

To analyze retrospectively results of reverse transcription polymerase chain reaction (RT-PCR) testing and demographic information in patients with known or suspected Ewing sarcoma/primitive neuroectodermal tumor family of tumors referred to the National Cancer Institute and to describe factors influencing the determination of molecular marker status.

PATIENTS AND METHODS

Tumor samples from 76 patients from February 1997 to December 1999 were analyzed. In all cases, the diagnosis of this family of tumors was confirmed by histopathologic review.

RESULTS

In 58 patients, the presence of a translocation associated with this family of tumors was confirmed using RT-PCR. Specifically, there were 45 Ewing sarcoma (EWS)-FLI type 1 translocations, four EWS-FLI type 2 translocations, five EWS-ERG translocations, and four less common EWS-FLI variants. Of patients with a confirmed translocation, four were confirmed only after nested RT-PCR techniques were used. In five patients who initially underwent needle biopsy, the diagnosis was confirmed only after open biopsy or repeat needle biopsy was undertaken. Samples from 18 patients were translocation-negative. Of these, seven samples were deemed inadequate for RT-PCR testing as a result of inappropriate tissue handling or the presence of necrotic material. Five patients were found to have a different diagnosis after complete histopathologic and molecular characterization. Six samples remained, in which adequate tissue was obtained with no evidence of a characteristic translocation.

CONCLUSIONS

In apparently translocation-negative samples, close attention should be given to the possibility of an alternative diagnosis, the potential need for nested RT-PCR, and the possibility of an inadequate sample. Strong consideration should be given to the use of open biopsy as opposed to needle biopsy to avoid the need for repeat biopsies and the potential for inaccurate assessment of molecular marker status.

Soft tissue Ewing sarcoma--peripheral primitive neuroectodermal tumor with atypical clear cell pattern shows a new type of EWS-FEV fusion transcript

This study describes a new case of Ewing sarcoma (ES)-peripheral primitive neuroectodermal tumor (pPNET) with unusual phenotype and fusion gene structure. The tumor located in the inguinal area of a 15-year-old boy showed a highly aggressive behavior with hematogenous metastases after intensive chemotherapy and bone marrow transplant, causing death 28 months after diagnosis. The tumor displayed a clear cell pattern, and several neuroectodermal markers proved positive both in the original tumor and in xenografts. This neuroectodermal character was confirmed by electron microscopy. Moreover, cytogenetically the tumor has an unusual chromosomal rearrangement, t(2;22)(q13;q22,t(3;18)(p21;q23); representing a new EWS-FEV fusion type in which exon 7 of EWS gene is fused with exon 2 of FEV gene. This is the third published study of an ES-pPNET showing EWS-FEV fusion described, but it is the first study of a tumor with the aforementioned fusion points. These findings support the genetic and morphologic heterogeneity existing within the group of ES-pPNET tumors.

A link between basic fibroblast growth factor (bFGF) and EWS/FLI-1 in Ewing's sarcoma cells

The EWS/FLI-1 fusion gene is characteristic of most cases of Ewing's sarcoma and has been shown to be crucial for tumor transformation and cell growth. In this study we demonstrate a drastic down-regulation of the EWS/FLI-1 protein, and a growth arrest, following serum depletion of Ewing's sarcoma cells. This indicates that growth factor circuits may be involved in regulation of the fusion gene product. Of four different growth factors tested, basic fibroblast growth factor (bFGF) was found to be of particular significance. In fact, upon treatment of serum-depleted cells with bFGF, expression of the EWS/FLI-1 protein and growth of the Ewing's sarcoma cells were restored. In addition, a bFGF-neutralizing antibody, which was confirmed to inhibit FGF receptor (FGFR) phosphorylation, caused down-regulation of EWS/FLI-1. Experiments using specific cell cycle blockers (thymidine and colcemide) suggest that EWS/FLI-1 is directly linked to bFGF stimulation, and not indirectly to cell proliferation. We also demonstrated expression of FGFRs in several tumor samples of Ewing's sarcoma. Taken together, our data suggest that expression of FGFR is a common feature of Ewing's sarcoma and, in particular, that the bFGF pathway may be important for the maintenance of a malignant phenotype of Ewing's sarcoma cells through up-regulating the EWS/FLI-1 protein. Oncogene (2000) 19, 4298 - 4301

Three-dimensional spectral precision distance microscopy of chromatin nanostructures after triple-colour DNA labelling: a study of the BCR region on chromosome 22 and the Philadelphia chromosome

Topological analysis of the three-dimensional (3D) chromatin nanostructure and its function in intact cell nuclei implies the use of high resolution far field light microscopy, e.g. confocal laser scanning microscopy (CLSM). However, experimental evidence indicates that, in practice, under biologically relevant conditions, the spatial resolution of CLSM is limited to about 300 nm in the lateral direction and about 700 nm in the axial direction. To overcome this shortcoming, the use of a recently developed light microscopical approach, spectral precision distance microscopy (SPDM) is established. This approach is based on the precise localization of small labelling sites of a given target in spectrally differential images. By means of quantitative image analysis, the bary centres (intensity weighted centroid analogous to the centre of mass) of these independently registered labelling sites can be used as point markers for distance and angle measurements after appropriate calibration of optical aberrations (here, polychromatic shifts). In combination with specific labelling of very small chromatin target sites with dyes of different spectral signatures by fluorescence in situ hybridization (FISH), SPDM presently allows us to analyse the nuclear topology in three-dimensionally conserved nuclei with a 'resolution equivalent', many times smaller than the conventional optical resolution. Chronic myelogeneous leukaemia (CML) is genetically characterized by the fusion of parts of the BCR and ABL genes on chromosomes 22 and 9, respectively. In most cases, the fusion leads to a translocation t(9; 22) producing the Philadelphia chromosome. SPDM was applied to analyse the 3D chromatin structure of the BCR region on the intact chromosome 22 and the BCR-ABL fusion gene on the Philadelphia chromosome (Ph) by using a new triple-colour FISH protocol: two different DNA probes were used to detect the BCR region and the third DNA probe was used to identify the location of the ABL gene. Consistent 3D distance measurements down to values considerably smaller than 100 nm were performed. The angle distributions between the three labelled sites on the Philadelphia chromosome territory were compared to two state-of-the-art computer models of nuclear chromatin structure. Significant differences between measured and simulated angle distributions were obtained, indicating a complex and non-random angle distribution.

Characterization of chromosomal breakpoints in an ALL patient using cross-species color banding

Cross-species color-banded karyotype (Rx-FISH) results were compared with those of conventional G-banded metaphases from the same sample. Breakpoints and karyotype were confirmed as 46,XX,t(8;22)(q24;q11), der(9)t(1;9)(q21;p13) through the novel technology of cross-species color banding in an acute leukemic patient (ALL, L3); the karyotype was 46,XX,t(8;22)(q24;q11),der(9)t(1;9)(q25;p24) by conventional G-banding.

The topological organization of chromosomes 9 and 22 in cell nuclei has a determinative role in the induction of t(9,22) translocations and in the pathogenesis of t(9,22) leukemias

The neighborhood relationships of chromosomes can be of great importance for basic cellular processes such as gene expression or translocation induction. In this study, the topological organization of chromosomes 9 and 22 was investigated in cell nuclei of G0-phase lymphocytes. We found that the territories of both chromosomes are predominantly located in the central region of cell nuclei. In addition to this, chromosomes 9 and 22 were frequently associated in pairs detected as false-positive ABL-BCR fusions. Both effects might substantially increase the probability of interaction between chromosomes. Because of this, exchange aberrations were studied in chromosomes 9 and 22 of human lymphocytes irradiated by neutrons. The rate of aberration induction between these chromosomes was 11 times higher than the expected frequency based on the fractional molecular weight of these chromosomes. We show that the increased rate of exchange between chromosomes 9 and 22 induced by neutrons corresponds to the neighborhood relationships of both chromosomes. Similar topological characteristics of ABL and BCR genes were found in several cell lines: T- and B-lymphocytes. HL60 cells and bone marrow cells. This finding suggests that the specific chromatin structure mentioned might be responsible for the high rate of induction of t(9;22)-positive leukemias in the human population.

RT-PCR evaluation of peripheral blood, bone marrow and peripheral blood stem cells in children and adolescents undergoing VACIME chemotherapy for Ewing's sarcoma and alveolar rhabdomyosarcoma

Peripheral blood stem cell support allows dose intensification of multiple cycle chemotherapy for metastatic tumors, including pediatric sarcomas. The VACIME protocol (vincristine, adriamycin, cyclophosphamide, ifosfamide, mesna and etoposide) utilizes peripheral blood stem cells (PBSC) collected following the treatment cycle as support for subsequent dose- and time-intensive chemotherapy. A critical assumption is that PBSC collected in this manner will be purged of residual tumor cells in vivo. We tested this assumption using sensitive reverse-transcriptase polymerase chain reaction (RT-PCR) to assess the presence of the characteristic translocations of the Ewing's sarcoma family of tumors (ESFT) and alveolar rhabdomyosarcoma (ARMS), t(11;22), and t(2;13), respectively. We used RT-PCR to evaluate 122 samples of peripheral blood (PB), bone marrow (BM) and PBSC collected from 12 pediatric patients with metastatic ESFT and ARMS. The samples included pre-therapy BM and PB, as well as BM, PB, and PBSC collections at various times in the VACIME treatment course. Molecular evidence of tumor contamination was detected in 1/40 PBSC collections from 12 patients. In all patients, we documented clearance of disease by RT-PCR in peripheral blood and bone marrow by week 9 of the VACIME protocol. In vivo purging in combination with the intensive VACIME regime appears to be effective in removing tumor cells from PBSC, bone marrow, and peripheral blood as detected by RT-PCR.

Clinical, morphological, cytogenetic and molecular aspects of a series of Ph-negative chronic myeloid leukemias

Clinical, morphological, cytogenetic and molecular (fluorescence in situ hybridization and RT-PCR) data were analyzed in twelve Philadelphia negative chronic myeloid leukemias (Ph-negative CMLs). Four patients were classified as BCR-positive. A standard b2a2 or b3a2 transcript was found, and the BCR-ABL hybrid gene was located on the 22q11 band in three cases and on the 1p35 band in one case with a t(1;9)(p35;q34). All were classified as typical chronic granulocytic leukemia (CGL) according to the French-American-British (FAB) morphological guidelines. Responses to therapy were evaluated by FISH in the four patients, and proved to be poorer than in Ph-positive CMLs. Eight BCR-negative patients were identified. They could be characterized by an older age, a less proliferative form of disease than the BCR-positive patients, and a frequent (six out of eight) abnormal karyotype. The FAB classification identified four CGLs and four atypical CMLs (aCML). A normal karyotype was more frequent in the patients classified as CGL whereas all the aCMLs had a chromosomal abnormality. Three patients had chromatin clumping and this morphologic feature was associated with trisomy 8 in two. No correlation between the cytogenetic, morphologic and the clinical data were found. Five patients had poor tolerance to therapy with a frequent occurrence of bone marrow failure and hemorragic syndrome, whereas three patients responded to a standard treatment of CML. Our study reinforces previous data on Ph-negative BCR-positive CMLs and emphasizes the difficulty in correlating clinical, morphologic, cytogenetic data in Ph-negative BCR-negative CMLs. However, our data also argue in favor of the existence of true Ph-negative BCR-negative CMLs and suggest that some of them can respond to a standard treatment of CML.

Frequent expression of human Thy-1 antigen on pre-B cell acute lymphoblastic leukemia with t(9;22)

Thy-1 (CDw90) is a phosphatidylinositol-anchored protein, and is expressed on human pluripotential hematopoietic stem cells. The expression pattern of this antigen on leukemia cells is still controversial. In this study, 72 adult patients with pre-B cell acute lymphoblastic leukemia (pre-B ALL) were examined for the expression pattern of Thy-1 by using indirect immunofluorescence and reversed transcription polymerase chain reaction (RT-PCR) methods. Twelve cases were judged positive on the basis of conventional immunophenotype criteria. Thirteen cases showed a weak clonal shift on the fluorogram, even though their positive percentages were from 6.7% to 14.9%. Thy-1 gene transcripts were detected in all of the 13 cases showing a weak clonal shift. The study of antibody binding capacity, which was calculated by the mean fluorescence intensity of the test sample on the basis of a calibration curve using standard beads, showed that cases with more than 150 sites/cell could be positive. Thy-1 positivity in pre-B ALL was not associated with the expression of B-cell differentiation antigens. Thy-1 expression was significantly higher in pre-B ALL cases with karyotypic abnormalities than in those with normal karyotype (p = 0.0071). The t(9;22) abnormality was found in 18 of the 25 Thy-1+ cases. Simultaneous expression of transcriptional factors, GATA-2 and SCL, was frequently detected in the Thy-1+ cases. bcr-abl and GATA-2 are thought to play important roles in the proliferation of immature hematopoietic cells. Indeed, cell-cycle analysis showed that the cell population in the S/G2/M phase of the present Thy-1+ cases was less than that in the Thy-1- cases (p = 0.001770). Our data suggest that Thy-1 expression indicates the proliferative status of the leukemia cells, not their phenotypic immaturity.

Monozygotic twins concordant for Cayler syndrome

Deletions within chromosome band 22q11.2 are associated with a variety of conditions, although a simple genotype-phenotype correlation has not been established so far. Environmental factors, chance events, or a second hit theory were supported by two observations of monozygotic twins with 22q11.2 deletions and discordant phenotypes [Goodship et al., J Med Genet 1995;32:746-748; Fryer, J Med Genet 1996;33:173]. We present monozygotic twins concordant for 22q11.2 deletion and Cayler syndrome, favoring the view that there exists a predominant genetic determination of the del 22q11.2 phenotype. As these twins are diamniotic and dichorionic, they may offer a more reliable insight in genetic phenotype determination than the other published, probably monochorionic, twins who may have a discordant malformation by twinning itself.

Goosecoid-like sequences and the smallest region of deletion overlap in DiGeorge and velocardiofacial syndromes

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Structure and chromosomal assignment to 22q12 and 17qter of the ras-related Rac2 and Rac3 human genes

Members of the Rho/Rac/Cdc42Hs family of GTPases have been shown to participate in many aspects of the signaling of cell growth and differentiation. Although the biochemical properties of these GTPases have been extensively studied, very little is known about the structure of the corresponding genes. To gain insight on the evolution of the Rho family, we were interested in studying the genomic structure of several members. We report here the structure and the localization to 22q12 of the human Rac2 gene, as well as the localization to 17qter of Rac3, a new member closely related to Rac1 and Rac2. Unlike the structure of its closest relative ARH-G gene, which contains a single intron, Rac2 is made of at least 7 exons, spanning over 18 kb of DNA. Comparison of gene structure and exonic borders suggests that the emergence of the whole superfamily took place early during evolution.

Distribution of ABL and BCR genes in cell nuclei of normal and irradiated lymphocytes

Using dual-color fluorescence in situ hybridization (FISH) combined with two-dimensional (2D) image analysis, the locations of ABL and BCR genes in cell nuclei were studied. The center of nucleus-to-gene and mutual distances of ABL and BCR genes in interphase nuclei of nonstimulated and stimulated lymphocytes as well as in lymphocytes stimulated after irradiation were determined. We found that, after stimulation, the ABL and BCR genes move towards the membrane, their mutual distances increase, and the shortest distance between heterologous ABL and BCR genes increases. The distribution of the shortest distances between ABL and BCR genes in the G0 phase of lymphocytes corresponds to the theoretical distribution calculated by the Monte-Carlo simulation. Interestingly, the shortest ABL-BCR distances in G1 and S(G2) nuclei are greater in experiment as compared with theory. This result suggests the existence of a certain regularity in the gene arrangement in the G1 and S(G2) nuclei that keeps ABL and BCR genes at longer than random distances. On the other hand, in about 2% to 8% of lymphocytes, the ABL and BCR genes are very close to each other (the distance is less than approximately 0.2 to 0.3 microm). For comparison, we studied another pair of genes, c-MYC and IgH, that are critical for the induction of t(8;14) translocation that occurs in the Burkitt's lymphoma. We found that in about 8% of lymphocytes, c-MYC and IgH are very close to each other. Similar results were obtained for human fibroblasts. gamma-Radiation leads to substantial changes in the chromatin structure of stimulated lymphocytes: ABL and BCR genes are shifted to the nuclear center, and mutual ABL-BCR distances become much shorter in the G1 and S(G2) nuclei. Therefore, we hypothesize that the changes of chromatin structure in the irradiated lymphocytes might increase the probability of a translocation during G1 and S(G2) stages of the cell cycle. The fact that the genes involved in the t(8;14) translocation are also located close together in a certain fraction of cells substantiates the hypothesis that physical distance plays an important role in the processes leading to the translocations that are responsible for oncogenic transformation of cells.

Unusual segregation of t(11;22) resulting from crossing-over followed by 3:1 disjunction at meiosis I

Reciprocal translocation t(11;22)(q23;q11) is of particular interest because the unbalanced offspring of the translocation carriers usually present with a supernumerary derivative chromosome 22. This common unbalanced karyotype is the result of 3:1 chromosome segregation during meiosis. We report the third case of a rare segregation pattern of a paternal 11;22 translocation. The proband's karyotype revealed the presence of a der(11) and two copies of a der(22), i.e. 47,XX,t(11;22)(q23;q11),+der(22) t(11;22)pat. The karyotype is the result of paternal 3:1 segregation after crossing-over involving the derived and the normal chromosome 22, as revealed by chromosome polymorphism analysis. Contrary to the preferential maternal, transmission of this common unbalanced translocation, the data from the literature, including our case, may suggest preferential paternal transmission of this rare type of unbalanced translocation.

Neutrophilic-chronic myeloid leukemia: a distinct disease with a specific molecular marker (BCR/ABL with C3/A2 junction)

Neutrophilic-chronic myeloid leukemia (CML-N) is a rare myeloproliferative disorder that runs a much more benign course than chronic myeloid leukemia, and for which no specific underlying molecular lesion has been described so far. We have analyzed the genomic DNA by Southern blotting and the BCR/ABL hybrid gene transcripts by reverse transcriptase-polymerase chain reaction in three patients with clinical findings of CML-N, who did have a t(9;22) chromosomal translocation. In all patients we have found a rare type of BCR/ABL rearrangement, with a breakpoint between exons c3 and c4 of the BCR gene (corresponding to BCR exons 19 and 20). This was confirmed by hybridization with an oligonucleotide probe spanning the c3/a2 region. This type of junction causes almost the entire BCR gene to fuse with ABL. The junction is in frame and it gives rise to a fusion protein of predicted 230 kD. Our data now provide a molecular diagnostic marker for CML-N, and they are consistent with the notion that the inclusion or exclusion of BCR exons in the fusion protein affects dramatically its capacity to derange myeloid proliferation and differentiation, leading to the appearance of different disease phenotypes.