A complex chromosome rearrangement forms the BCR-ABL fusion gene in leukemic cells with a normal karyotype

Chromosome in situ hybridization studies showed that the normal karyotype of leukemic cells from a patient with Ph1-negative, BCR-positive chronic myeloid leukemia (CML) concealed a complex t(9;22;20)(q34;q11;p13). The close association of 5'-BCR and 3'-ABL was demonstrated by field inversion gel electrophoresis, and in situ hybridization showed that BCR-ABL was located on the short arm of chromosome 20. Our findings further indicate that chromosome rearrangement is the cause of BCR-ABL gene fusion in leukemic cells that show a normal karyotype. Results from in situ hybridization studies were consistent with formation of the t(9;22;20) by a two step chromosomal rearrangement, but field inversion gel electrophoresis results indicated a more complex rearrangement.     

Complex de novo rearrangement of chromosome 9 with clinical features of monosomy 9p syndrome

A girl with a complex rearrangement of chromosome 9 is reported. She shows the characteristic clinical features of monosomy 9p syndrome. The rearrangement was apparently preceded by four breaks which resulted in a presumptive tiny deletion of the distal end of the short arm, inversion of the rest of this arm and a proven deletion of the secondary constriction region of the long arm. By means of C-banding, it was possible to demonstrate the paternal origin of the rearranged chromosome 9. Finally, it is shown that the region determining the phenotypic expression of monosomy 9p syndrome is seemingly located at band 9p24.     

Complex chromosomal translocations in the Philadelphia chromosome leukemias. Serial translocations or a concerted genomic rearrangement?

Joining of the BCR and ABL genes is an essential feature of the group of human leukemias characterized by the Philadelphia chromosome and there is recent evidence that the human BCR-ABL fusion gene induces leukemia in experimental animals. Joining of these two genes is the result of cytogenetic translocation, usually the t(9;22)(q34;q11), but sometimes of more complex translocations involving one or more chromosomes in addition to chromosomes 9 and 22. The leukemic cells of some patients carry the BCR-ABL fusion gene but have an apparently normal karyotype. Recent studies show that these cells conceal complex chromosome rearrangements. Because the BCR-ABL fusion gene appears to be the result of cytogenetic rearrangement in all cases of these leukemias, the causes and mechanism of chromosome rearrangement will be relevant to the development of leukemia in man. We examine mechanisms of chromosome rearrangement and propose that both simple and complex chromosome translocations result from a single, though sometimes complex, interchange event.     

Partial DiGeorge syndrome in two patients with a 10p rearrangement

We describe 2 patients with a partial DiGeorge syndrome (facial dysmorphism, hypoparathyroidism, renal agenesis, mental retardation) and a rearrangement of chromosome 10p. The first patient carries a complex chromosomal rearrangement, with a reciprocal insertional translocation between the short arm of chromosome 10 and the long arm of chromosome 8, with karyotype 46, XY ins(8;10) (8pter 8q13::10p15-->10p14::8q24.1-->8qter) ins(10:8) (10pter--> 10p15::8q24.1-->8q13::10p14-->10qter). The karyotype of the second patient shows a terminal deletion of the short arm of chromosome 10. In both patients, the breakpoints on chromosome 10p reside outside the previously determined DiGeorge critical region II (DGCRII). This is in agreement with previous reports of patients with a terminal deletion of 10p with breakpoints distal to the DGCRII and renal malformations/hypoparathyroidism, and thus adds to evidence that these features may be caused by haploinsufficiency of one or more genes distal to the DGCRII.     

Cytogenetic characterization of a BCR-ABL transduced mouse cell line

Most patients with Philadelphia (Ph)-positive acute lymphoblastic leukemia (ALL) show evidence of secondary chromosome aberrations that may influence the course of disease and response to treatment. To better understand how these secondary chromosomal aberrations occur and to investigate whether the p185/p190 BCR-ABL fusion protein may directly induce an increased chromosomal instability and subsequently the appearance of clonal chromosome aberrations, three BRC-ABL (p185/ p190)-transduced mouse pre-B cell lines were analyzed by spectral karyotyping and fluorescence in situ hybridization. The human wild-type BCR-ABL gene was expressed at a level comparable with that in human Ph-positive leukemias at diagnosis. All BCR-ABL-transduced cell lines acquired similar clonal chromosomal aberrations. Trisomy 5 was always present, followed by loss of the Y chromosome, trisomy of chromosomes 12 and 18, and an unbalanced translocation between chromosomes X and 12. Thus, ectopic p185/p190 BCR-ABL expression, such as p210 BCR-ABL, PML-RARA, or C-MYC transduction, may induce an increased chromosomal instability leading to clonal karyotypic evolution, which may mimic secondary chromosome aberrations in human Ph-positive ALL.     

Involvement of the short arm of the derivative chromosome 9 in Philadelphia-positive acute lymphoblastic leukemia

Three Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL) patients showed rearrangement of the short arm of the chromosome 9 involved in Ph formation. At diagnosis, blast cells were morphologically L2 and phenotypically B-cell precursors, as shown by common ALL antigen (CALLA), B1, B4 and HLA-DR positivity. Cytogenetically, they had in common the presence of cells with normal karyotypes, the Ph, involvement of band 9p13----p21, and loss of region 9p13----9pter. In our experience, involvement of the p arm of the derivative chromosome 9 in Ph+ leukemias is a very rare event found in ALLs only.     

Mosaic rearrangement of chromosome 18: characterization by FISH mapping and DNA studies shows trisomy 18p and monosomy 18p both of paternal origin

Structural abnormalities of chromosome 18p mainly consist of isochromosomes of the short arm, which result in tetrasomy 18p. Trisomy 18p is much rarer, and less well characterized. We report on a 12-year-old girl with minor facial anomalies, delayed development, abnormal hands, atopic dermatitis, and hearing loss. She was mosaic for two abnormal cell lines in peripheral blood. In 90% of cells, a dicentric chromosome with duplication of the whole short arm of chromosome 18 resulted in trisomy 18p; 10% of cells had monosomy 18p, arising from a t(14;18)(p11;q11). FISH mapping, with multiple region specific and locus specific probes from the short and long arm of chromosome 18, showed that the structure of the dicentric chromosome 18 was 18pter-->18q23::18q11-->18pter. DNA polymorphisms for chromosome 18 showed that the abnormalities of chromosome 18 were paternal in origin. Combining all results, we could link the trisomy 18p and monosomy 18p to a common origin via a complex series of events in an early mitosis.     

Clinical implications of fluorescence in situ hybridization analysis in 13 chronic myeloid leukemia cases: Ph-negative and variant Ph-positive.

Thirteen chronic myeloid leukemia (CML) patients, 10 with variant Philadelphia (Ph) translocations and 3 Ph negative cases, were analyzed by fluorescence in situ hybridization (FISH) with the use of BCR and ABL cosmid probes and a chromosome 22 painting probe. In the variant Ph translocations, the BCR-ABL fusion gene was located on the Ph chromosome; in 1 CML Ph-negative patient, the BCR-ABL fusion gene was located on the Ph chromosome; and, in 2 patients, it was located on chromosome 9. The chromosome 22 painting probe was detected on the third-party chromosome of the variant translocation, and in none of the variant translocations was there any detectable signal on chromosome 9. In CML patients with clonal evolution of a simple Ph, a signal of the chromosome 22 painting probe was detected on the der(9) of the Ph translocation. It was concluded that the variant Ph translocations evolved simultaneously in a three-way rearrangement. The clinical parameters of the 13 patients were similar to those of a large group of CML patients with a simple Ph translocation. It is suggested that, to determine the prognosis of CML patients with a complex karyotype, FISH analysis with a chromosome 22 painting probe be performed.     

dic(9; 20): A new recurrent chromosome abnormality in adult acute lymphoblastic leukemia

Loss of chromosome 20 and rearrangement of the short arm of chromosome 9 were identified by banding analysis of three adult patients with acute lymphoblastic leukemia (ALL). The G-banding pattern suggested and identical deletion of 9p, but, also, an unbalanced translocation with chromosome 20 was taken into consideration. Dual-color chromosome painting with probes for chromosomes 9 and 20 revealed the presence of material from chromosome 20 at the short arm of the abnormal chromosome 9 in all three cases. Centromeric alpha-satellite DNA of both chromosome 9 and chromosome 20 was demonstrated by fluorescence in situ hybridization and indicated the presence of a dicentric chromosome. The hybridization of a YAC clone of the short arm of chromosome 20 proved that the dicentric chromosome contained the short arm of chromosome 20, which had been suspected from the G-banding pattern. Thus, the rearrangement was interpreted as dic(9; 20)(pl I;qi I . ? I). Because this was the sole chromosome abnormality in two patients, dic(9; 20) may be a primary chromosome aberration in ALL. In one case, a 9q⁺ chromosome derived from a Philadelphia (Ph) translocation was involved in the formation of the dicentric chromosome. Immunophenotyping revealed CD 1o⁺ B-cell precursor ALL in all three cases. Whereas the two patients in whom dic(9; 20) was the sole cytogenetically detectable change are in continuous complete remission for 10 and 45 months, respectively, the Ph⁺ patient relapsed with leukemia and died 8 months after diagnosis. © 1995 Wiley-Liss, Inc.     

Patient with rheumatoid arthritis and MCA/MR syndrome due to unbalanced der(18) transmission of a paternal translocation t(18;20)(p11.1;p11.1)

A girl with psychomotor retardation and a pattern of minor anomalies was found to have a slightly enlarged short arm of chromosome 18 by conventional GTG-banded chromosome examination. The 18p+chromosome has also been found in the father. FISH studies using chromosome 18-and chromosome 20-specific painting probes confirmed a reciprocal whole arm translocation between chromosomes 18 and 20 in the father, resulting in monosomy of the short arm of chromosome 18 and trisomy of the short arm chromosome 20 in the patient. FISH analysis using a chromosome 18 alpha-satellite-specific probe showed a reduced signal intensity. The patient presented with a flat, oval face, upslanting palpebral fissures, periorbital fullness, and mental retardation; she also had chronic diarrhea with milk protein intolerance and juvenile rheumatoid arthritis at age 5 years. Juvenile rheumatoid arthritis, like several other immunologic disorders, has occasionally been reported in patients with deletion of 18p, and thus most likely loss of a gene or genes on 18p is responsible for various immunologic disorders occurring in these patients.     

Jumping translocation of chromosome 14 in a skin squamous cell carcinoma from a xeroderma pigmentosum patient

The cytogenetic study of a case of cutaneous squamous cell carcinoma developed in a child affected by xeroderma pigmentosum is described. In this paratetraploid tumor, virtually all mitoses had the following rearrangements: i(1q), i(1p), t(3q14q), del(9p), and der(19)t(8;19). In addition, there were several deletions of 1p and 1q. The del(9p) likely occurred as the first rearrangement. The distal segment of the short arm of chromosome #9 and the long arm of #19 and #22 were the most underrepresented and chromosome #6 the most overrepresented chromosome or chromosome segment. The most striking anomaly detected was a jumping translocation of chromosome #14, involved with chromosomes #1, #3, #5, #7, #9, #14, and #22. The breakage of chromosome #14 always occurred on the short arm.     

A case of insertional translocation involving chromosomes 2 and 4

We report on a 6-year-old Caucasian boy with direct insertion of genetic material from the short arm of chromosome 4 to the short arm of chromosome 2. He was referred for evaluation because of global developmental delay and seizure disorder. A karyotype performed at 41/2 months of age, by a laboratory elsewhere, reportedly showed a deletion of chromosome 4(p12). When we saw him, he had macrocephaly, hypotonia, psychomotor retardation, multiple minor congenital anomalies, and EEG abnormalities. Repeat chromosomes performed by our laboratory revealed that his karyotype was 46, XY, dir ins(2;4)(p24;p15.3p13).
Fluorescence in situ hybridization (FISH) analysis, using chromosomes 2 and 4 painting probes confirmed that material from 4p has been translocated to 2p. Also, FISH analysis using the Wolf-Hirschhorn critical region probe revealed that both loci are intact. Parental chromosomes were normal. This complex rearrangement, though it appears balanced, probably might have resulted in either a structural loss of genetic material or functional loss of a gene action. Thus, his phenotype could be explained by this de novo insertion of chromosome 4 material into chromosome 2. There is no reported case of this specific chromosome rearrangement.     

A new genomic mechanism leading to cri-du-chat syndrome

Using standard banding techniques, a within-arm intrachromosomal insertion can be mistakenly interpreted as a paracentric inversion. The need to correctly distinguish between these two types of chromosome rearrangements is emphasized by their different reproductive risks. For carriers of an intrachromosomal insertion, the empiric risk of having a liveborn child with a recombinant chromosome leading to a genetic imbalance is at least 15%, whereas the risk for a carrier of a paracentric inversion having a liveborn child with a recombinant chromosome leading to a genetic imbalance is thought to be practically negligible. We report a unique observation in which a paracentric inversion in the short arm of chromosome 5, 46,XX,inv(5)(p13.3p15.3), was identified in a women who had a daughter with an apparently terminal deletion in the distal short arm of chromosome 5, 46,XX,del(5)(p14.3), and the clinical diagnosis of cri-du-chat syndrome. We further characterized the rearrangement, and fluorescence in situ hybridization (FISH) and microsatellite analyses confirmed the paracentric inversion in the mother and showed the deletion in the daughter was maternal in origin. Therefore, this represents a case in which a confirmed paracentric inversion likely resulted in a viable terminal deletion. We propose a mechanism involving dicentric chromosome formation with subsequent breakage and telomere healing during meiosis. This illustrates a new genomic mechanism of chromosome rearrangement leading to cri-du-chat syndrome and should provide significant information for the medical management of patients with other terminal deletion syndromes.     

A patient with isochromosome 18q, radial-thumb aplasia, thrombocytopenia, and an unbalanced 10;18 chromosome translocation

We report on the clinical and cytogenetic findings in a newborn with a de novo isochromosome 18q. Radial/thumb aplasia and thrombocytopenia were significant features in addition to multiple congenital anomalies. Comparison with reported cases suggests that the genes for such features are located on the 18q arm. An additional finding of a non-reciprocal translocation between chromosome 18p telomere and chromosome 10q telomere was also observed in a majority of cells examined. This additional rearrangement likely has minimal phenotypic consequences, but does raise the possibility that cryptic translocations of telomeric ends of the deleted arm in isochromosome cases may be more common than appreciated.     

Fluorescence in situ hybridization characterization of different cryptic BCR-ABL rearrangements in chronic myeloid leukemia

Using fluorescence in situ hybridization probes, obtained from bacterial artificial chromosome (BAC) libraries that relate to sequences either side of the BCR and ABL genes, this study characterized four chronic myeloid leukemia cases with cryptic BCR-ABL rearrangements. Each case showed evidence of a different underlying mechanism: one case showed a microinsertion of BCR into ABL, another a microinsertion of ABL into BCR, and the third showed a complex rearrangement including deletion of adjacent flanking sequences, consistent with the reverse translocation model of cryptic rearrangement. The fourth case also showed evidence of a more complex rearrangement involving chromosome 1.     

Prenatal diagnosis and characterization of an unbalanced whole arm translocation resulting in monosomy for 18p

Monosomy for the short arm of chromosome 18 is one of the most frequent autosomal deletions observed. While most cases result from terminal deletion of 18p, 16% of cases reported were as a result of an unbalanced whole arm translocation resulting in monosomy 18p. The origin and structure of these derivative chromosomes were reported in only a few cases. We report the prenatal diagnosis and characterization of a new case of monosomy 18p as a result of an unbalanced whole arm translocation. Amniocentesis was performed at 15 weeks of gestation on a 34-year-old woman initially referred for advanced maternal age. Holoprosencephaly was identified by ultrasound at the time of amniocentesis. Karyotype analysis showed an unbalanced whole arm translocation between the long arm of one chromosome 18 and the long arm of one chromosome 22, 45,XX,der(18;22)(q10;q10), in all metaphases. In effect, the fetus had monosomy for 18p. Parental karyotypes were normal, suggesting a de novo origin for the der(18;22). Fluorescence in situ hybridization (FISH) analysis was performed with alpha-satellite probes D18Z1 and D14Z1/D22Z1 to identify the origin of the centromere on the der(18;22). Signal was observed with both probes, indicating that the centromere was composed of alpha-satellite DNA from both constituent chromosomes. Genotyping of the fetus and her parents with chromosome 18p STS marker D18S391 showed only the paternal 187 bp allele was present in the fetus, indicating that it was the maternal chromosome 18 involved in the der(18;22). This case and previous reports show that de novo unbalanced whole arm translocations are more likely to retain alpha-satellite sequences from the two chromosomes involved.     

Fluorescence in situ hybridization detection of two telomeres on the short arm of a derived chromosome 16 in an infant with thrombocytopenia

We report a case of severe thrombocytopenia with an abnormal bone marrow karyotype described by G-banding analysis as t(16;21)(p?13;q11). Using fluorescence in situ hybridization (FISH) analysis with whole chromosome paints, the chromosome rearrangement was shown to be more complex, with the additional cryptic involvement of the long arm of chromosome 3. The chromosome rearrangement involved the breakpoints 3q26, 16p13.3, and 21q11; this rearrangement has not been previously described. The size of genomic material translocated from the chromosome 16 homologue was too small to be detected by chromosome paint. A 16p-specific telomeric probe was hybridized to locate the translocated 16p material. The 16p telomeric unique sequence DNA was retained on the der(16) chromosome, indicating a more distal breakpoint. This study demonstrates that telomeric translocations can occur that would be undetected by telomeric-specific FISH probes.