Ring chromosome

About: Ring chromosome is a research topic. Over the lifetime, 1546 publications have been published within this topic receiving 31061 citations. The topic is also known as: supernumerary circular chromosome.

Telomeric 22q13 deletions resulting from rings, simple deletions, and translocations: cytogenetic, molecular, and clinical analyses of 32 new observations

Abstract: The terminal regions of human chromosomes are known to contain specialised DNA sequences and may be vulnerable to rearrangements causing human genetic diseases and particularly idiopathic mental impairment.1,2 During the last decade, there have been several reports of patients who are described as having a 22q13 monosomy resulting from simple terminal deletions.1,3–11 A common phenotype emerged from these reports, including variable learning difficulties with disproportionate verbal delay, generalised hypotonia, normal to accelerated growth, and minor facial dysmorphy.10 Monosomies for 22q13 have also been reported that result from unbalanced translocation with an acrocentric short arm.10,12 The acrocentric short arms only bear ribosomal genes, and their duplication or deletion is not generally thought to be phenotypically significant. Therefore such translocations can be considered as “pure” terminal 22q13 deletions. A distinct group of 22q13 monosomies has been reported that result from the formation of a ring chromosome which combines loss of some long arm material with loss of part of the short arm, with no clinical consequences. Nevertheless, although ring chromosome 22 has been described in over 50 cases,13 it remains uncertain whether the variable phenotype is caused by the loss of a variable amount of chromosomal material or by a cellular mosaicism arising from instability of the ring. Regardless of the causative rearrangement, very few cases of “pure” 22q13 monosomy have been investigated up to now by detailed molecular studies. In order to characterise this syndrome better, facilitate the diagnosis, and provide targeted health care for affected individuals, we have studied 33 patients (32 new observations) with a pure 22q13 partial monosomy, using molecular and cytogenetic methods. ### Subjects Our study involved 33 patients with a “pure” partial 22q13 monosomy, with exclusion of all rearrangements involving loss or gain of euchromatic material from any other …

The structure and dynamics of ring chromosomes in human neoplastic and non-neoplastic cells.

Abstract: Acquired ring chromosomes have been found in most types of human neoplasia, with a frequency approaching 10% in malignant mesenchymal tumours. In this study, the composition and dynamics of ring chromosomes were analysed in eight cases of acute myelogenous leukaemia, 17 solid tumours, and five cases with constitutional rings. Chromosomal banding and fluorescence in situ hybridisation were performed to determine the content and the structural heterogeneity of the rings. Telomeric repeats were detected using peptide nucleic acid probes or primed in situ labelling, whereas centromeric activity was evaluated by detection of kinetochore proteins. Mitotic instability was assessed by the frequency of anaphase bridges. The results suggest that human ring chromosomes can be structurally and functionally divided into two categories. In the first of these, size variation is minimal and rearrangement at cell division is uncommon. The majority of such rings contain subtelomeric sequences. Constitutional ring chromosomes and most rings in leukaemias belong to this group, whereas only a few mesenchymal tumours exhibit rings of this type. The second category consists of rings with amplified sequences, primarily from chromosome 12, characteristically occurring in atypical lipomatous tumours and other subtypes of low or borderline malignant mesenchymal neoplasms. Variation in size and number is extensive, and breakage-fusion-bridge events occur at a high frequency. Abnormalities in pericentromeric sequences are common and, in some cases, kinetochores assemble in the absence of alphoid DNA. We conclude that it is not only the ring structure per se or the neoplastic nature of the host cell that determines ring instability, but probably also the functional role of the genes carried in the ring.

Chromosomal aberrations in heavy smokers.

Abstract: Lymphocyte chromosomes from 20 heavy smokers were analyzed from 48-h whole blood cultures for the frequency of dicentric chromosomes, ring chromosomes, and chromatid translocations. Compared to controls, these exchange type aberrations occurred more frequently in the smokers.