Cases reported "Ring Chromosomes"

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1/32. Simultaneous occurrence of two supernumerary autosomal ring chromosomes r(1) and r(16) in twins.

    ring chromosomes are estimated to occur in 3/10000 newborns and the simultaneous occurrence of two autosomal rings must be a very rare event. Recently, the characterisation of these markers using fluorescence in situ hybridisation (FISH) has greatly enhanced cytogenetic-phenotypic correlations in patients with these marker chromosomes. This kind of analysis enabled us to clarify a unique karyotype containing a r(1) and a r(16) in identical twins born after a 26 week gestation with minimal somatic abnormalities. The origin of the rings was identified using a satellite and whole chromosome painting probes. FISH analysis showed the same abnormal female karyotype in both twins, 48,XX, r(1)(p13q21), r(16)(p11q11).ish r(1) (D1Z5 ,wcpl ), r(16)(D16Z2 ,wcp16 ) in about two thirds of the cells. Each also had minor clones with a normal female karyotype or with one or the other supernumerary ring. Half of the r(1) contained CBG band negative material and the r(16) appeared to be totally CBG band positive. These twins represent the second report of the simultaneous occurrence of multiple autosomal rings. Their description may help to delineate a new chromosome disorder and shows the usefulness of FISH analysis.
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2/32. Neocentromere formation in a stable ring 1p32-p36.1 chromosome.

    Neocentromeres are functional centromeres formed in chromosome regions outside the normal centromere domains and are found in an increasing number of mitotically stable human marker chromosomes in both neoplastic and non-neoplastic cells. We describe here the formation of a neocentromere in a previously undescribed chromosomal region at 1p32-->p36.1 in an oligospermic patient. Cytogenetic GTL banding analysis and the absence of detectable fluorescence in situ hybridisation (FISH) signals using telomeric probes indicate the marker to be a ring chromosome. The chromosome is negative for CBG banding and is devoid of detectable centromeric alpha satellite and its associated centromere protein CENP-B, suggesting activation of a neocentromere within the 1p32-36.1 region. Functional activity of the neocentromere is shown by the retention of the ring chromosome in 97% of the patient's lymphocytes and 100% of his cultured fibroblasts, as well as by the presence of key centromere binding proteins CENP-E, CENP-F, and INCENP. These results indicate that in addition to CENP-A, CENP-C, and CENP-E described in earlier studies, neocentromere activity can further be defined by CENP-F and INCENP binding. Our evidence suggests that neocentromere formation constitutes a viable mechanism for the mitotic stabilisation of acentric ring chromosomes.
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3/32. Amplification of the MLL gene on double minutes, a homogeneously staining region, and ring chromosomes in five patients with acute myeloid leukemia or myelodysplastic syndrome.

    gene amplification is one of the mechanisms for activating proto-oncogenes resulting in an enhanced expression of the corresponding gene product. By fluorescence in situ hybridization (FISH), amplification of the proto-oncogene MLL has been described only in seven patients with acute myeloid leukemia (AML). We report five new patients (four had de novo AML, one had a de novo myelodysplastic syndrome) displaying different mechanisms of MLL amplification, suspected by G-banding and confirmed by FISH analysis. In two patients, MLL was amplified on double-minute chromosomes (dmins). In both cases, an interstitial deletion in 11q23 including the MLL gene was associated with the occurrence of the dmins containing MLL. As a rarely described mechanism, MLL amplification in the form of size-variable ring chromosomes was observed in two patients. Remodeling of the ring chromosomes leads to multiple copies of MLL and obviously provided a selective growth advantage. In one of the two cases with ring chromosomes, the centromeric alpha-satellite dna of the ring chromosome was not detectable. Our fifth patient showed the unique finding of MLL amplification within a uniformly (homogeneously?) stained region in interaction with amplified ribosomal dna sequences. Also, one of the patients with ring chromosomes exhibited the amplification of ribosomal dna on the ring chromosomes. The transcriptionally active genes for ribosomal rna could probably enhance the expression of MLL. In one of our five patients, we found the new combination of concomitant amplification of the proto-oncogenes MLL and MYC.
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4/32. Mother and daughter with 45,X/46,X,r(X)(p22.3q28) and mental retardation: analysis of the X-inactivation patterns.

    We report on a mother and daughter both with a 45,X/46,X,r(X)(p22. 3q28) karyotype and mental retardation. fluorescence in situ hybridization (FISH) and microsatellite analyses for 14 loci/region at Xp22.3 and seven loci/region at Xq28 indicated that the ring x chromosome was missing a roughly 12-Mb region from Xp22.3 with the breakpoint between DXS85 and DXS9972, and another region of less than 100 kb from Xq28 with the breakpoint distal to the region defined by the FISH probe c8.2/1. X-inactivation analysis, using the methylation status of the AR gene (exon 1) as an indicator, showed that the normal and ring X chromosomes in the X,r(X)(p22.3q28) cell lineage were randomly inactivated. The Xp22.3 deleted region partially overlaps with the regional intervals of MRX19, MRX21, MRX24, MRX37, MRX43, and MRX49 associated with heterozygote manifestation. Therefore, it is likely that one or more of these MRX genes, subject to X-inactivation, are lost from the ring x chromosome, and that reduced expression of the MRX gene(s) caused by random X-inactivation has resulted in mental retardation in the mother and daughter.
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5/32. Novel ring chromosome composed of X- and Y-derived material in a girl with manifestations of Ullrich-turner syndrome.

    We present a female infant who has a novel genetic variant of Ullrich-turner syndrome. Chromosome analysis on amniotic fluid cells obtained because of ultrasound observation of nuchal thickening showed 45,X in all cells. The infant was born with a low posterior hairline and moderate edema over hands and feet. Postnatal chromosome analysis demonstrated two cell lines-47% of the metaphases were 45,X, but 53% had a ring chromosome in addition to the normal X. FISH studies using alpha satellite probes, an X-whole-chromosome-paint (WCP) probe, and a Y-cocktail probe determined that the ring was composed of both X and Y sequences. FISH studies also determined that the KAL locus was present on the ring, but that XIST was absent. PCR-based analysis of lymphocyte dna documented that the ring contained sequences from both the short and the long arm of the y chromosome. X-chromosome analysis using a panel of highly polymorphic markers indicated that the ring contained material derived only from Xp22.1 to Xp21.3. No Xq material was identified on the ring, and androgen receptor-based X-inactivation studies suggested that the intact x chromosome was not subject to random X inactivation.
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6/32. Boy with bilateral retinoblastoma due to an unusual ring chromosome 13 with activation of a latent centromere.

    We present a patient with bilateral retinoblastoma and developmental delay who has an abnormal male karyotype containing 47 chromosomes, including an acentric derivative chromosome 13. We postulate that the derivative 13 occurred after a break at 13q14, with the proximal portion of the chromosome forming a ring and the distal portion undergoing duplication. Thus, this patient is trisomic for 13q14-->qter. The derivative chromosome with duplicated distal portion (13q14-->qter) lacked the 13 centromere and was negative for chromosome 13 alpha-satellite dna by low stringency FISH. Nevertheless, this chromosome is stably transmitted in lymphocytes and fibroblasts. A single primary constriction was observed at band 13q21, consistent with activation of a latent centromere (neocentromere) at this band. The neocentromere on der(13) was positive for multiple centromeric proteins, suggesting that it acts as the functional centromere. By FISH, the Rb gene was present on the normal 13, the proximally derived ring chromosome, but not on the derivative chromosome. Although there was no evidence for disruption of the Rb gene, this chromosome rearrangement most likely results in abnormal expression of the Rb gene product. copyright Wiley-Liss. Inc.
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7/32. Detailed characterization of 12 supernumerary ring chromosomes using micro-FISH and search for uniparental disomy.

    Twelve patients with varying degrees of mosaicism for a supernumerary ring chromosome were studied. The ring chromosomes were characterized using microdissection in combination with degenerate nucleotide-primed polymerase chain reaction (PCR) and reverse painting (micro-FISH). This method made it possible to determine the chromosomal origin of the ring chromosomes in detail, and thus to compare the phenotypes of similar cases. Eleven of the marker chromosomes were derived from the most proximal part of 1p, 3p, 3q, 5p, 7q, 8p, 8q, 9p, 10p and 20p. One marker chromosome had a complex origin, including the proximal and the most distal part of 20q. Eight of the families were also investigated for uniparental disomy (UPD) using microsatellite analysis. One case with maternal UPD 9 was found in a child with a ring chromosome derived from chromosome 9, r(9)(p10p12).
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8/32. Kabuki syndrome-like features associated with a small ring chromosome X and XIST gene expression.

    Although clinical features in Kabuki syndrome (KS; Niikawa-Kuroki syndrome) have been well defined, the underlying genetic mechanism still remains unclear. We report a 9-year-old girl with typical KS-like facial appearance, skeletal and dermatoglyphic abnormalities, severe mental retardation, and growth deficiency. In 60 of 100 GTG-banded metaphases from peripheral blood lymphocytes, a ring chromosome smaller than a G group chromosome was found, which, according to reverse painting, consisted of Xq11.1q13. The proband's karyotype was described as mos45,X/46,X, r(X). Several loci were analyzed with fluorescence in situ hybridization (FISH) and microsatellite markers revealing that one r(X) breakpoint mapped proximal to DXS422 (Xp11.21) and the second mapped distal to XIST gene, between loci DXS128E and DXS441 (Xq13.2). uniparental disomy for X and r(X) was excluded and the paternal origin of r(X) was identified. XIST expression was demonstrated by nested reverse transcription polymerase chain reaction (RT-PCR) using primers spanning exons 5, 6i, and 6 in rna prepared from lymphocytes. The observation of XIST expression is in contrast to two other cases in which the XIST gene was either not present on r(X) or not expressed. To our knowledge, this is the first case of Kabuki-like syndrome manifestations with r(X) and XIST expression.
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9/32. Identification of a small supernumerary marker chromosome, r(2)(p10q11.2), and the problem of determining prognosis.

    The identification of small supernumerary marker chromosomes (SMCs) and the elucidation of their clinical significance remain two of the problems in classical human cytogenetics. We observed a small supernumerary ring in amniotic fluid cell cultures and identified its origin as r(2)(p10q11.2) and its extent by means of fluorescent in situ hybridisation (FISH). uniparental disomy (UPD) was excluded by microsatellite analysis using polymorphic markers localised in the same region. On the basis of normal ultrasonographic checks, the patient decided to continue the pregnancy. A normal female was delivered at term and subsequent neonatal follow-ups confirmed the normal phenotype and development. In the present case, genetic counselling was not helpful because of the absence of reference cases. Detailed characterisation made it possible to correlate the normal baby phenotype with the trisomic 2p10-2q11.2 genomic region. Further molecular cytogenetic investigations of SMCs classified by dna content and pregnancy outcome data should improve genetic counselling and risk evaluation.
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10/32. Ring chromosome 21 in a boy and a derivative chromosome 21 in the mother: implication for ring chromosome formation.

    We report on r(21) chromosome in a boy and a der(21) chromosome in his mother. Cytogenetic studies revealed a mosaic 45,XY[4]/46,XY,r(21)[96] karyotype in the boy and a 46,XX,der(21)[100] karyotype in the mother. fluorescence in situ hybridization analysis for D21Z1 at the centromere, AML1 at 21q22.1, LSI21 at 21q22.2, and 21qtel at the telomere region showed that the r(21) chromosome retained single copies of D21Z1, AML1, and LSI21 and lacked the 21qtel, whereas the der(21) chromosome had two copies of the 21qtel on both of its ends and single copies of D21Z1, AML1, and LSI21, with a paracentric inversion of AML1 and LSI21 (21qtel-D21Z1-LSI21-AML1-21qtel). Microsatellite analysis for nine loci on 21q22.3 indicated that the r(21) chromosome was missing a distal 21q22.3 region involving D21S1890, D21S1411, and D21S1903 with no maternally derived alleles, and that the der(21) chromosome was associated with duplication of a distal 21q22.3 region encompassing D21S1890 and D21S1446. The results suggest that a U-type exchange occurred between the homologous distal 21q regions duplicated on the der(21) chromosome, leading to the r(21) formation. This is a novel mechanism put forward for the formation of a monocentric ring chromosome.
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