Cases reported "Chromosome Breakage"

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11/15. Breakpoint mapping in a case of mosaicism with partial monosomy 9p23 --> pter and partial trisomy 1q41 --> qter suggests neo-telomere formation in stabilizing the deleted chromosome.

    We report on a clinical and molecular cytogenetic study of a patient who presents a complex chromosomal rearrangement with two different cell lines. Using high-resolution GTG banding and fluorescence in situ hybridization (FISH) with several probes, including bacterial artificial chromosomes (BACs), the karyotype was defined as 46,XX,del(9)(p23)[54]/46,XX,der(9)t(1;9)(q41;p23)[46], indicating the presence of monosomy 9p23 in all cells and trisomy 1q41 in approximately 50% of the cells. The patient studied presents most of the manifestations of the 9p deletion and 1q duplication syndromes. The breakpoint was mapped at 9p23 with a loss of approximately 13.9-Mb of dna. The duplicated segment consists of approximately 35 Mb from 1q41-qter region. We also suggest that a mechanism for telomere capture and interstitial telomeric sequences (ITs) is involved in a neo-telomere formation in one of the cell lines. This study highlights the importance of combining high-resolution chromosome and FISH with BACs in order to make genotype-phenotype correlations and to understand the mechanisms involved chromosomal aberrations.
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ranking = 1
keywords = partial trisomy, trisomy
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12/15. A father and son with mental retardation, a characteristic face, inv(12), and insertion trisomy 12p12.3-p11.2.

    A male patient with mental retardation (MR) and mild facial features was shown by high-resolution G-banding to have pericentric inversion of chromosome 12 with an unknown segment inserted into the long arm of the inverted chromosome [46,XY,inv(12)(pter-->p11.2::q14.1-->p11.2::?::q14.1-->qter)]. Both the inverted chromosome 12 and clinical manifestations were transmitted to his son. Karyotypes of the propositus' parents were normal. Studies with fluorescence in situ hybridization (FISH) in both the propositus and his son revealed that the extra segment was derived from 12p. Further FISH mapping and the genome-wide copy number detection by GeneChip Mapping 100K Array showed that an 11-Mb segment of 12p between two BAC clones, RP11-22H10 and RP11-977P2, was inserted at one of the reunion points in the long arm of the inv(12) chromosome. Analysis of parent-child transmissions of duplicated alleles using microsatellite markers defined the maternal origin of the chromosomal anomaly in the propositus and suggested a mechanism of its formation through a sister-chromatid rearrangement (SCR), that is, mismatched pairing and unequal crossover between sister chromatids as well as three break rearrangements including a U type rearrangement. Karyotypes of the propositus and his son were thus inv(12)(pter-->p11.22::q14.1-->p12.3::q14.1-->qter). This is the first report of "pure" proximal 12p-trisomy including p12.3-p11.22 region.
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ranking = 0.35815747571455
keywords = trisomy
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13/15. 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.
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ranking = 0.14326299028582
keywords = trisomy
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14/15. trisomy 15 rescue with jumping translocation of distal 15q in prader-willi syndrome.

    We report a patient with prader-willi syndrome (PWS) and mosaicism for a de novo jumping translocation of distal chromosome 15q, resulting in partial trisomy for 15q24-qter. A maternal uniparental heterodisomy for chromosome 15 was present in all cells, defining the molecular basis for the PWS in this patient. The translocated distal 15q fragment was of paternal origin and was present as a jumping translocation, involving three different translocation partners, chromosomes 14q, 4q, and 16p. The recipient chromosomes appeared cytogenetically intact and interstitial telomere dna sequences were present at the breakpoint junctions. This strongly suggests that the initial event leading to the translocation of distal 15q was a non-reciprocal translocation, with fusion between the 15q24 break-point and the telomeres of the recipient chromosomes. These observations are best explained by a partial zygotic trisomy rescue and comprise a previously undescribed mechanism leading to partial trisomy.
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ranking = 0.53581574757146
keywords = partial trisomy, trisomy
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15/15. Centromeric dna break in a 10;16 reciprocal translocation associated with trisomy 16 confined placental mosaicism and maternal uniparental disomy for chromosome 16.

    Stable centromeric breakage in non-acrocentric chromosomes and balanced reciprocal translocation mosaicism are both rare events. We studied a family in which the mother had mosaicism for a balanced reciprocal translocation between chromosomes 10 and 16 which was associated with a break in chromosome 16 centromere alpha-satellite dna inverted question mark146,XX,t(10;16)(q11.2;q11.1) [29]/46,XX[25] inverted question mark. The derivative chromosome 16 contained only a very small amount of 16 alpha-satellite dna while the derivative 10 contained all of the 10 alpha-satellite dna as well as a large amount of the 16 alpha-satellite dna. The same translocation was present in all cells in her son who was found prenatally to have trisomy 16 mosaicism inverted question mark46,XY,t(10;16) (q11.2;q11.1)mat[22]/47,idem, 16[4] inverted question mark. trisomy 16 cells were subsequently determined to be confined to the placenta. dna polymorphism analyses in the family demonstrated maternal uniparental disomy for chromosome 16 in the diploid child. The child, at age 7 months, had minor facial anomalies similar to a previously reported case of maternal uniparental disomy for chromosome 16. In addition to illustrating several rare events, this family further demonstrated that substantial deletion of the centromeric alpha-satellite dna does not impair centromere function and both mitotic and meiotic stability are retained in such cases.
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ranking = 0.35815747571455
keywords = trisomy
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