Leukemic recombinations involving heterochromatin in myeloproliferative disorders with t(1;9)

The unbalanced t(1;9) is a rare, recurrent rearrangement in polycythemia vera (PV) resulting in trisomy of both 1q and 9p arms, whereas a balanced t(1;9)(q12;q12), to our knowledge, has never been reported before. We studied two patients with PV and one with idiopathic myelofibrosis bearing an unbalanced t(1;9) and one patient with essential thrombocythemia with a balanced t(1;9). In all cases fluorescence in situ hybridization showed that the breakpoints were located within the satellite II family of heterochromatin of chromosome 1 and the satellite III of chromosome 9. Heterochromatin breakage and reunion produce the unbalanced t(1;9) and may contribute to a gene dosage effect due to gains of 1q and 9p. Case 4 with the balanced t(1;9), however, suggests that translocation of heterochromatin close to critical genes could interfere with their function. The molecular event underlying juxtaposition of satellite II of chromosome 1 and the satellite III of chromosome 9 remains to be elucidated.     

Trisomy 1q generating translocations in Wilms tumor

Unbalanced translocations generating trisomy of 1q are common in Wilms tumor (WT). We present eight unbalanced 1q translocations from seven tumors and a review of the literature. An unbalanced translocation that results in a der(16)t(1q;16q) chromosome represents more than half of the published +1q generating translocations in WT. This translocation is also common to many other tumor types. Four of the tumors presented here contained this chromosome and,in two cases, it was the primary acquired cytogenetic abnormality within the tumor. The other four translocations involved 9q31, 9q34, 17p1?, and 21p11 as the partner to 1q. The chromosome 17 and 21 translocations occurred within the same tumor as apparently independent events. In contrast with the 16q translocations, these other translocations were secondary cytogenetic events, thereby indicating a role in tumor progression rather than initiation. Probes mapping to 1q12 and 1q21 were employed for fluorescence in situ hybridization and it was demonstrated that different 1q breakpoints are possible. In this series, the majority of breakpoints either mapped to 1q12 or were centromeric to this region.     

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.     

The first recurring chromosome translocation in hepatoblastoma: Der(4)t(1;4)(q12;q34)

We report four cases of hepatoblastoma with a derivative chromosome 4 from an unbalanced translocation between the long arms of chromosomes 1 and 4, an aberration reported only rarely in isolated cases of other types of neoplasms. The abnormality in three hepatoblastomas was der(4)t(1;4)(q12;q34), whereas the fourth case appeared to have a der(4)t (q25;q32). All had hyperdiploid tumor karyotypes; however, in the case with t(q25;q32), the der(4) was the only abnormality in the stemline. We speculate that the oncogenetic event in our cases may be the loss of a gene or genes on distal 4q or their alteration by juxtaposition to 1q12 heterochromatin. Genes Chromosom. Cancer 19:291–294, 1997. © 1997 Wiley-Liss, Inc.     

Dual-color fish analysis of breakpoints on robertsonian translocations

Summary We investigated six Robertsonian translocations, including two cases of rob(13q14q), one of rob(14q21q), one of rob(13q22q), and two of rob(21q21q), by means of fluorescencein situ hybridization (FISH) using five repetitive DNA probes: two alpha-satellite DNAs (D21Z1/D13Z1 and D14Z1/D22Z1), satellite III DNA, beta-satellite DNA, and ribosomal DNA. Single color FISH successfully defined the breakpoints in four cases of the six. Since the remaining two cases, rob(13q22q) and rob(21q21q), revealed to retain rDNA, we tried to define the breakpoints in detail by dual color FISH in these rare types. In the rob(13q22q) the chromosomal breakage on chromosome 22 was likely to have occurred within the rDNA region and that the chromosome 13 breakpoint was within the alpha-satellite region. In one rob(21q21q) case we defined the breakpoint on one chromosome distal to, or within, the beta-satellite region distal to the rDNA, and the other chromosome breakage had occurred within alpha-satellite DNA. Our results underscored the power of dual-color FISH for defining the precise locations of breakpoints in Robertsonian translocations.     

Unique t(Y;1)(q12;q12) reciprocal translocation with loss of the heterochromatic region of chromosome 1 in a male with azoospermia due to meiotic arrest: a case report

A de novo reciprocal translocation 46,X,t(Y;1)(q12;q12) was found in an azoospermic male with meiotic arrest. Cytogenetics and fluorescent in situ hybridization (FISH) were used to define the karyotype, translocation breakpoints and homologue pairing. SRY (Yp), Yq11.2-AZF regions, DAZ gene copies and the distal Yq12 heterochromatin were studied by PCR and restriction analysis using sequence-tagged sites and single nucleotide variants. High resolution GTL, CBL and DA-DAPI staining revealed a (Y;1) translocation in all metaphases and a normal karyotype in the patient's father. FISH showed the presence of the distal Yq12 heterochromatic region in der(1) and loss of the heterochromatic region of chromosome 1. PCR demonstrated the intactness of the Y chromosome, including the SRY locus, AZF regions, DAZ genes and distal heterochromatin. A significant decrease (P = 0.005) of Xp/Yp pairing (18.6%), as compared with controls (65.7%), was found in arrested primary spermatocytes, and cell culture and mRNA expression studies confirmed an irreversible arrest at meiosis I, with induction of apoptosis and removal of germ cells by Sertoli cells. We characterized a de novo t(Y;1)(q12;q12) balanced reciprocal translocation with loss of the heterochromatic region of chromosome 1, that caused unpairing of sex chromosomes followed by meiosis I arrest, apoptotic degeneration of germ cells and azoospermia.     

Recurrent chromosome aberrations in human lung squamous cell carcinomas

Cytogenetic study of seven cases of previously untreated lung squamous cell carcinomas (SQC) is reported. Chromosome numbers vary from 38 to 538, with a majority of hypotriploid karyotypes with complex rearrangements. The numbers of recurrent imbalances were evaluated in considering the average number of chromosomes or chromosome segments in each analyzed metaphase and for each case. In decreasing order of frequency, deficiencies for 3p, 5q, 8p, Y, 5p, 10p, 13, and, to a lesser degree, for 8q, 9, 10q, 11pter, 14, 15, and 21 were observed; the excesses principally involve 1q, 3q, and 7q. In three tumors, homogeneously staining regions were observed at various chromosome sites. Most chromosome rearrangements occurred after breakage in constitutive heterochromatin, and no recurrent breakpoints were found in euchromatin except 11p15. The major consequences of these anomalies may be chromosomal imbalances, leading to hemizygosity and perhaps related to gene dosage, rather than to alterations of genes.     

Kallmann syndrome in a boy with a t(1;10) translocation detected by reverse chromosome painting.

Prometaphase chromosomes from a 16 year old boy with hypogonadotrophic hypogonadism and anosmia (Kallmann syndrome) showed a tiny chromosome fragment attached to the long arm of one chromosome 1 without a visible reciprocal translocation chromosome. Chromosome painting with libraries from chromosomes 1 and X excluded a t(X;1) translocation, but failed to detect a second translocation chromosome. Through reverse chromosome painting, an unbalanced der(1), t(1;10) (q44;q26) translocation could be detected. This is the third case of Kallmann syndrome with a de novo rearrangement between two autosomes. The distal long arm of chromosome 1 may contain a candidate locus for a gene, mutations of which may cause the Kallmann phenotype; a 10q location seems less likely.     

Correlation of DNA hypomethylation at pericentromeric heterochromatin regions of chromosomes 16 and 1 with histological features and chromosomal abnormalities of human breast carcinomas

Changes in DNA methylation status are not only important for regulating gene expression but are also suggested to induce chromosome instability. To reveal the correlation of DNA methylation status in heterochromatin regions with tumor histology and with chromosome alterations, DNA methylation status was examined by Southern blot analysis, and numerical and structural chromosome alterations, including the formation of der(16)t(1;16)/der(1;16), were examined by fluorescence in situ hybridization at the two loci in the pericentromeric satellite 2 regions of chromosomes 16 and 1 in 39 human breast carcinomas. DNA hypomethylation at the D16Z3 and the D1Z1 loci was detected in 31% (12 of 39) and 36% (12 of 33) of carcinomas, respectively, and mostly concurred. DNA hypomethylation was more frequent in the carcinoma group of more aggressive histological types or grade 3 than in the carcinoma of less aggressive histological types or grades 1 and 2, and tended to be more frequent in carcinomas with > or =4 copies of chromosomes 16 and/or 1 than in carcinomas with < or =3 copies of any of these chromosomes. The frequency of DNA hypomethylation at the D16Z3 and the D1Z1 loci was 45% (10 of 22) and 53% (9 of 17) in carcinomas without der(16)t(1;16)/der(1;16), formation, but only 12% (2 of 17) and 19% (3 of 16) in carcinoma with der(16)t(1;16)/der(1;16), respectively (P = 0.036 and 0.070). The 16q breakage was almost equally detected between carcinoma groups with and without the DNA hypomethylation. DNA hypomethylation in the satellite 2 regions was suggested to be associated with the accumulation of a large number of numerical chromosome alterations and involved in the development of breast carcinomas of aggressive histological features. On the contrary, chromosome instability induced by mechanisms other than DNA hypomethylation in heterochromatin regions might cause the formation of der(16)t(1;16)/der(1;16) and less aggressive breast carcinomas.     

Low level of DNA repair in human chromosome 1 heterochromatin

Band 1q12 is a breakage prone region commonly involved in chromosome 1 rearrangements found in human cancer. We have investigated whether a lack of DNA repair can account for the observed 1q12 fragility. Ethyl methanesulfonate (EMS)-induced repair sites originating in G₀/G₁ phase of the cell cycle were converted to chromosome breaks by blocking the re-synthesis step of excision repair with cytosine arabinoside. Thus, unfilled repair gaps reached S-phase and were detected as chromosome breaks after cell division. Chromosome breakage in the overall genome was monitored by scoring of micronuclei. Breaks in 1q12 were detected in interphase lymphocytes by in situ hybridization with tandem probes targeting the chromosome 1 centromere (D1Z5) and the adjacent heterochromatic band 1q12 (pUC1.77). Mitomycin-C (0.12 and 0.24 μg/ml) and X-rays (1 and 2 Gy) were used as positive controls to check the suitability of the tandem labelling approach in detecting 1q12 clastogenicity. Our data indicated that, although the methodology was suitable to detect 1q12 breakage and a high level of overall genome DNA repair occurred, there was a low level of EMS-induced DNA repair sites in 1q12 converted to hromosome breaks. This finding was consistent throughout G₁ phase, suggesting that there is a relatively low level of DNA excision repair in human chromosome 1 heterochromatin. Genes Chromosomes Cancer 20:173–184, 1997. © 1997 Wiley-Liss, Inc.     

Array-based comparative genomic hybridization facilitates identification of breakpoints of a novel der(1)t(1;18)(p36.3;q23)dn in a child presenting with mental retardation

Monosomy of distal 1p36 represents the most common terminal deletion in humans and results in one of the most frequently diagnosed mental retardation syndromes. This deletion is considered a contiguous gene deletion syndrome, and has been shown to vary in deletion sizes that contribute to the spectrum of phenotypic anomalies seen in patients with monosomy 1p36. We report on an 8-year-old female with characteristics of the monosomy 1p36 syndrome who demonstrated a novel der(1)t(1;18)(p36.3;q23). Initial G-banded karyotype analysis revealed a deleted chromosome 1, with a breakpoint within 1p36.3. Subsequent FISH and array-based comparative genomic hybridization not only confirmed and partially characterized the deletion of chromosome 1p36.3, but also uncovered distal trisomy for 18q23. In this patient, the duplicated 18q23 is translocated onto the deleted 1p36.3 region, suggesting telomere capture. Molecular characterization of this novel der(1)t(1;18)(p36.3;q23), guided by our clinical array-comparative genomic hybridization, demonstrated a 3.2 Mb terminal deletion of chromosome 1p36.3 and a 200 kb duplication of 18q23 onto the deleted 1p36.3, presumably stabilizing the deleted chromosome 1. DNA sequence analysis around the breakpoints demonstrated no homology, and therefore this telomere capture of distal 18q is apparently the result of a non-homologous recombination. Partial trisomy for 18q23 has not been previously reported. The importance of mapping the breakpoints of all balanced and unbalanced translocations found in the clinical laboratory, when phenotypic abnormalities are found, is discussed.     

Hypomethylation of chromosome 1 heterochromatin DNA correlates with q-arm copy gain in human hepatocellular carcinoma

Using comparative genomic hybridization (CGH) analysis, we, and others, have shown that there is a high and consistent incidence of chromosome 1q copy gain in human hepatocellular carcinoma (HCC). Chromosome 1 rearrangements, that involved peri-centromeric breakpoints, have also been frequently reported in karyotypic studies of HCC. Satellite DNA hypomethylation has been postulated as the mechanism underlying the induction of chromosome 1 peri-centromeric instability in many human cancers and in individuals with the rare recessive disorder ICF (immunodeficiency, centromeric heterochromatin instability, facial anomalies). In this study, we have investigated the role of DNA hypomethylation in 1q copy gain in HCC by examining the methylation status of chromosome 1 heterochromatin DNA (band 1q12). Thirty-six histologically confirmed samples of HCC were studied (24 paired tumor and adjacent nontumorous liver tissues, and 12 tumor only). Hypomethylation of satellite 2 (Sat2) DNA in 1q12 was analyzed by Southern blotting using methyl-sensitive enzyme digestion. In parallel, all cases were analyzed by CGH. A strong correlation between hypomethylated Sat2 sequences and 1q copy gain with a 1q12 breakpoint was found (P < 0.001). We postulate that such hypomethylation alters the interaction between the CpG-rich satellite DNA and chromatin proteins, resulting in heterochromatin decondensation, breakage and aberrant 1q formation. Spectral karyotyping further supported the presence of fragile 1q12 in HCC. Of particular interest was the finding of Sat2 DNA hypomethylation in 5 of 24 adjacent nontumorous liver tissues examined. These tissues showed no evidence of malignancy on histological examination nor did they display any CGH abnormalities. Our findings suggest a role for Sat2 demethylation in the early stages of the stepwise progression of liver carcinogenesis.     

High incidence of familial breast cancer segregates with constitutional t(11;22)(q23;q11)

In a family with a high incidence of postmenopausal breast cancer and a case of glioblastoma, the constitutional translocation t(11;22)(q23;q11.2) was shown to segregate with the malignancies. The breakpoints in this family coincided with the common breakpoints in t(11;22) as shown by a translocation-specific PCR assay. Loss of heterozygosity analysis of breast tumor tissue revealed deletion of the normal chromosome 22, but retention of der(22) in the tumor cells, suggesting a predisposing effect of the der(22) for breast and brain tumor development in this family.     

Maternal balanced translocation leading to partial duplication of 4q and partial deletion of 1p in a son: Cytogenetic and FISH studies using band-specific painting probes generated by chromosome microdissection

A 9-month-old boy with pre- and post-natal growth retardation, microcephaly, plagiocephaly, and several minor anomalies had the initial karyotype: 46,XY,der(1)t(1;?)(p36.1;?). Further analysis showed that the der(1) was derived from an unfavorable segregation of a maternal complex chromosome rearrangement, i.e., 46,XX,der(1)t(1;?)(p36.1;?), der(4)t(4;?)(q?;?). Whole chromosome fluorescence in situ hybridization (FISH) and chromosome microdissection were used to clarify the maternal karyotype as: 46,XX,der(1)t(1;4)(4qter→4q33::1p36.13→1qter),der(4)t(1;4)inv(4)(4pter→ 4q31.3::1p36.33→1p36.13::4q33→4q31.3::1p36.33→1pter). Therefore, the karyotype of the boy actually was 46,XY,der(1)t(1;4)(p36.13;q33). Clinical comparison of the patient's clinical findings showed similarities to individuals with partial del(1p) and dup(4q). To our knowledge the above cytogenetic abnormalities have not been described previously. This case further demonstrates the advantages of chromosome microdissection and FISH in the identification of anomalous chromosome regions and breakpoints. Am. J. Med. Genet. 71:160–166, 1997. © 1997 Wiley-Liss, Inc.     

Derivative (1;18)(q10;q10): a recurrent and novel unbalanced translocation involving 1q in myeloid disorders.

We report two cases of hematological malignancies, comprising a case of myelodysplastic syndrome (MDS) that rapidly evolved into acute myeloid leukemia, and a case of myeloproliferative disorder (MPD), in which der(1;18)(q10;q10) was found as the sole acquired karyotypic abnormality. This observation indicates that the unbalanced translocation is a recurrent aberration in myeloid disorders. To the best of our knowledge, centromeric fusion between long arms of chromosomes 1 and 18, leading to a normal chromosome 18 substituted with a der(1;18) chromosome, is novel and has not been described in cancer. Mechanistically, either trisomy 1q or monosomy 18p that results from the translocation may potentially contribute to leukemogenesis. Finally, chromosomes with large constitutive heterochromatin bands such as chromosome 1 may be at risk of centromeric instability and be predisposed to centromeric fusion with other chromosomes.     

Identification of the origin of centromeres in whole-arm translocations using fluorescent in situ hybridization with α-satellite DNA probes

We detected 2 patients with whole-arm translocations resulting in a derivative chromosome consisting of 18q and 21q. Because the breakpoints were near the centromere, classical cytogenetic techniques could not determine the centromeric origin of the derivative chromosomes. Using nonradioactive in situ hybridization with a chromosome 18 α-satellite DNA probe (D18Z1), the centromeres in the abnormal chromosomes were determined to be from chromosome 18. The abnormality in one patient resulted in monosomy 18p with a karyotype 45, XX, ?18, ?21, + der(18)t(18;21) (p11;q11)mat complement. The second patient with a 46, XX, ?21, + der(18)t(18;21)(p11;q11) de novo karyotype had complete trisomy of 18q. In both cases the appropriate phenotype was observed.     

FISH studies identify the i(20q-) anomaly as a der(20)del(20)(q11q13)idic(20)(p11)

Fluorescence in situ hybridization (FISH) analyses were performed on six of seven patients who had been reported in 2004 to have an i(20q-) anomaly expressed as ider(20)(q10)del(20)(q11q13). The i(20q-) was investigated with a series of probes: a centromere-specific probe for chromosome 20, two paint probes for 20p and 20q, and a panel of locus-specific probes prepared from BAC/PAC clones mapped to 20p. The results showed that: (1) i(20q-) was a dicentric chromosome; (2) both of its arms comprised a deleted 20q and a small part of 20p near the centromere of chromosome 20; and (3) the breakpoints and reunion sites of i(20q-) differed, residing in the region 20p11.21-20p11.22 delineated by BAC/PAC clones RP11-96L6 and RP13-401N8. Thus, i(20q-) could be more precisely described as a der(20)del(20)(q11q13)idic(20)(p11).