A t(21q21q) Ring Chromosome

Orye, E; Craen, Margarita

doi:10.1159/000152658

Cited by 10 publications

(4 citation statements)

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“…The difference in intensity of hybridization of the abnormal to normal bands (Fig. 4C) 21 and r(21)s have been reported (10,11,13). The evidence that these rings follow a t(21q;21q) Robertsonian translocation is indirect and derives from the presence of a second cell line in these mosaic individuals that was 46,-21,+t(21q;21q).…”

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confidence: 60%

“…The proposed mechanism of ring formation, breakage of both short and long arms of a chromosome with subsequent end to end fusion (8), remains unproven. In several reports of acrocentric ring chromosomes, a Robertsonian translocation produced by short arm fusion has been observed in the patient, a parent, or a sibling (9)(10)(11)(12)(13)(14)(15)(16) (19). The R2-10 line was also back selected for loss of the r(21) (cell line R2-1OW-S5) by growth in nonselective (purine supplemented) medium, followed by selective medium with the addition of bromodeoxyuridine and light (22).…”

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confidence: 99%

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Molecular mechanism in the formation of a human ring chromosome 21.

Wong

Kazazian

Stetten

et al. 1989

Proc. Natl. Acad. Sci. U.S.A.

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We have characterized the structural rearrangements of a chromosome 21 that led to the de novo formation of a human ring chromosome 21 [r(21)]. Molecular cloning and chromosomal localization of the DNA regions flanking the ring junction provide evidence for a long arm to long arm fusion in formation of the r(21). In addition, the centromere and proximal long arm region of a maternal chromosome 21 are duplicated in the r(21). Therefore, the mechanism in formation of the r(21) was complex involving two sequential chromosomal rearrangements. (i) Duplication of the centromere and long arm of one maternal chromosome 21 occurred forming a rearranged intermediate. (ii) Chromosomal breaks in both the proximal and telomeric long arm regions on opposite arms of this rearranged chromosome occurred with subsequent reunion producing the r(21).Ring chromosomes in humans represent a class of aberrant chromosomes observed frequently in congenital anomalies and occasionally with normal phenotypes (1). Most ring chromosomes arise de novo, yet occasional familial transmission has been reported (2-5). The frequency of ring chromosomes is 1 in 25,000 recognized conceptions (6), and all human chromosomes have been observed as rings. Almost 50% of ring autosomes are derived from the acrocentric chromosomes (7). The proposed mechanism of ring formation, breakage of both short and long arms of a chromosome with subsequent end to end fusion (8), remains unproven. In several reports of acrocentric ring chromosomes, a Robertsonian translocation produced by short arm fusion has been observed in the patient, a parent, or a sibling (9)(10)(11)(12)(13)(14)(15)(16) (19). The R2-10 line was also back selected for loss of the r(21) (cell line R2-1OW-S5) by growth in nonselective (purine supplemented) medium, followed by selective medium with the addition of bromodeoxyuridine and light (22). For mapping, a panel of somatic cell hybrids, 72532X-6, 153E7bx, and 2FuR1 (23), with characterized rearrangements of human chromosome 21 was used (19).Cloning the Chromosomal Break Points. DNA from the patient's blood lymphocytes was digested with EcoRI and a size-selected library (7-9 kb) was made in Agtwes B. About 300,000 recombinant phage were screened (24) with pPW231C and a single clone, A21BP (Fig. 1B), was purified. DNA from the region on the 3' side of the break point was cloned (A2lpq) by using probe CW21A from a flow-sorted, HindIII-digested chromosome 21 library in Charon 21A (ID code, LL21NS02; American Type Culture Collection number, 57713).Immunofluorescence Studies. For quantification of DNA, photographic negatives of 4',6-diamidino-2-phenylindole (DAPI)-stained (25) images were scanned using a Loats (Westminster, MD) video densitometer equipped with a twodimensional gel-scanning software package. Indirect immunofluorescence was performed on mitotic spreads (26). Chromosomes were first stained with DAPI and then with a monoclonal anti-centromere antibody prepared against the cloned 80-kDa human autoantigen

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confidence: 60%

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confidence: 99%

Molecular mechanism in the formation of a human ring chromosome 21.

Wong

Kazazian

Stetten

et al. 1989

Proc. Natl. Acad. Sci. U.S.A.

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“…To our knowledge, this case represents the fourth report of a patient with a translocation mosaicism involving two cell lines, one with t(21q21q) and the other with a ring 21 chromosome derived from a dicentric 21q21q (Orye andCraen 1974, Dallapiccola et al 1982). Our patient differs from these other patients in that the chromosomal mosaicism was detected in the blood of the other patients, and the individuals had mild manifestations of DS while our patient did not.…”

Section: Case Reportmentioning

confidence: 79%

Atypical Down syndrome phenotype with severe developmental delay, hypertonia, and seizures in a child with translocation trisomy 21

Keppler‐Noreuil¹,

Welch²,

Major³

et al. 2002

Dev Med Child Neurol

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An infant is reported who presented with a de novo 21;21 translocation trisomy 21 and an atypical phenotype for Down syndrome (DS). Findings included microcephaly, small stature, downslanting palpebral fissures, absent Brushfield spots, moderate micrognathia, left ptosis, left torticollis, severe developmental delay, seizures, and hypertonia. Further clinical evaluation using both the diagnostic criteria for DS and the Jackson checklist of 25 signs was inconsistent with the diagnosis for DS. Blood karyotype revealed: 46,XX,+21,dic(21;21) (p11.2;p11.2). Fluorescence in situ hybridization (FISH) analysis confirmed the trisomy 21 translocation. Both parents had normal karyotypes. Chromosome and FISH analyses were performed on skin fibroblasts. These studies revealed mosaicism for a translocation trisomy 21 cell line as wel as a second cell line consisting of one normal chromosome 21 and a ring chromosome 21 derived from translocation 21q21q which appeared to have a deletion of the critical region for DS involving the distal portion of the thelong arm of chromosome 21. The chromosome findings illustrate an atypical phenotype in the spectrum of mosaic DS and suggest possible mechanisms for the variability of the phenotype. It also emphasizes the importance of evaluating other tissues for mosaicism when presented with atypical clinical findings.

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“…However, as duplication or deficiency of a short arm region (pl 1, 12 and/or 13) of a D-group chromosome has no effects on the phenotype of an individual who carries it, they reduce to examples of partial trisomies of distal 13q. Orye and Craen (1974) described a case of 21 trisomy/ring 2t mosaicism [46,XY,+t(21q21q)/46,XY,+r[t(21q21q)] ]. According to the authors the ring was derived from the t(21q21q) chromosome.…”

Section: Discussionmentioning

confidence: 99%