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.

Mechanisms of ring chromosome formation, ring instability and clinical consequences

Abstract: Background The breakpoints and mechanisms of ring chromosome formation were studied and mapped in 14 patients.

New chromosomal syndrome: Miller-Dieker syndrome and monosomy 17p13

Abstract: The Miller-Dieker Syndrome (MDS) consists of lissencephaly, characteristic facies, pre- and postnatal growth retardation, plus various other birth defects. Autosomal recessive inheritance has been presumed based on four reported families with two or more affected siblings. We present substantial evidence that monosomy 17p13.3 causes the MDS phenotype. This includes two patients with ring chromosome 17, one patient with a de novo 17p13 deletion, and one patient with monosomy 17p due to an unbalanced 7p; 17p translocation. We report the first prenatal diagnosis of MDS in a 20-week fetus from this latter family. Additionally, we report a balanced translocation between chromosome 17 and different autosomes (8, 12, and 15) in three of the four familial cases of lissencephaly. The finding of a chromosomal basis for this presumed autosomal recessive disorder significantly alters genetic counseling and makes prenatal diagnosis possible in some families.

Chemical Mutagens and Sister-Chromatid Exchange

Abstract: The recent introduction of the sister-chromatid exchange (SCE) test has revolutionized the cytogenetic approach to the identification of biologically hazardous chemicals. Increasingly, laboratories are turning to this technique in preference to scoring chromosome aberrations. This chapter explores some of the problems and perspectives of the SCE test and reviews some of the results obtained so far.

Combined spectral karyotyping and DAPI banding analysis of chromosome abnormalities in myelodysplastic syndrome.

Abstract: Spectral karyotyping (SKY) is a new molecular cytogenetic technique that allows simultaneous visualization of each chromosome in a different color. We have used SKY for comprehensive analysis of 20 myelodysplastic syndromes (MDSs) (13 primary MDSs, 3 therapy-related MDSs, and 4 acute leukemias developed from MDS, including 1 cell line established from a secondary leukemia), previously analyzed by G-banding. To locate the chromosomal breakpoints, DAPI-counterstained band images from all metaphases were transformed to G-band–like patterns. By using SKY, it was possible to identify the origin and organization of all clonal marker chromosomes (mar), as well as the origin of all abnormalities defined as additional material of unknown origin (add) or homogeneously staining regions (hsr) by G-banding. In total, SKY identified the chromosomal basis of 38 mar, add, and hsr, corrected 8 abnormalities misidentified by G-banding, and revealed 6 cryptic translocations in 5 cases. Total or partial chromosomal loss (mainly of -5/5q- and -7/7q-) is the most frequent cytogenetic abnormality in MDS. In 3 of 11 cases with -5/5q- and in 4 of 8 with -7/7q-, lost material was detected by SKY in unbalanced translocations. A total of 60 chromosomal losses were identified by G-banding in 16 cases with multiple chromosome abnormalities involving at least 3 chromosomes. For 26 of these losses (43%), SKY analysis suggested that the losses were not complete, but had been translocated to a variety of partner chromosomes. Moreover, SKY analysis revealed that a ring chromosome in a case of acute leukemia developed from MDS contained three to six segments that originated from chromosome 21 material. Fluorescence in situ hybridization showed the amplification of the AML1 gene on regions derived from chromosome 21, providing the first evidence of amplification involving this gene in MDS. Genes Chromosomes Cancer 26:336–345, 1999. © 1999 Wiley-Liss, Inc.

Molecular and phenotypic characterization of ring chromosome 22.

Abstract: We performed a phenotype study of 35 individuals (19 males, 16 females) with ring chromosome 22 or r(22) with a mean age of 10 years. In common with other studies, a phenotype of moderate-to-profound learning difficulties and delay or absence of speech affected all individuals with the exception of the case with the smallest deletion. Autistic traits were significantly associated with r(22), as shown by an autism screening questionnaire. Mild and variable dysmorphic features, predominantly craniofacial and distal limb, were observed. Internal organ involvement was uncommon. Even though ring chromosomes are reportedly associated with growth abnormalities, only 2 out of 24 individuals showed evidence of growth failure, while 2 showed accelerated growth. Chromosome 22 long arm deletions, as determined by hemizygosity for informative microsatellite markers, varied from <67 kb to 10.2 Mb in size (or <0.15 to 21% of total chromosome length), with no significant differences in the parental origin of the ring chromosome. Few phenotypic features correlated with deletion size suggesting a critical gene, or genes, of major effect lies close to the telomere. Loss of the SHANK3/PROSAP2 gene has been proposed to be responsible for the main neurological developmental deficits observed in 22q13 monosomies. This study supports this candidate gene by identifying a phenotypically normal r(22) individual whose ring chromosome does not disrupt SHANK3. All other r(22) individuals were hemizygous for SHANK3, and we propose it to be a candidate gene for autism or abnormal brain development.