Non C-banding variants in some normal families might be homogeneously staining regions

Webb, Graham C.; Krumins, Edgar J. M.; Eichenbaum, S.Z.; Voullaire, Lucille; Earle, Elizabeth D.; Choo, K. H. Andy

doi:10.1007/bf00288273

Cited by 24 publications

(9 citation statements)

References 17 publications

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“…In some of these (eg Family D in the study of Wang and Miller 25 ), the additional material in 9p originates from the satellite III DNA, similar to case 52 in the present study. The cases described by Webb et al 26 show more similarity to cases 50, 51 and 53 of the present study. Interestingly, Webb et al 26 detected an amplification of the 9ph+ region transmitted through all generations.…”

Section: Discussionsupporting

confidence: 81%

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Homologous sequences at human chromosome 9 bands p12 and q13-21.1 are involved in different patterns of pericentric rearrangements

Starke

Seidel

Henn³

et al. 2002

Eur J Hum Genet

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A thorough study of the heterochromatin organisation in the pericentromeric region and the proximal long (q) and short (p) arms of human chromsome 9 (HSA 9) revealed homology between 9p12 and 9q13-21.1, two regions that are usually not distinguishable by molecular cytogenetic techniques. Furthermore, the chromosomal regions 9p12 and 9q13-21.1 showed some level of homology with the short arms of the human acrocentric chromosomes. We studied five normal controls and 51 clinical cases: 48 with chromosome 9 heteromorphisms, one with an exceptionally large inversion and two with an additional derivative chromosome 9. Using fluorescence in situ hybridisation (FISH) with three differentially labelled chromosome 9-specific probes we were able to distinguish 12 heteromorphic patterns in addition to the most frequent pattern (defined as normal). In addition, we studied one inversion 9 case with the recently described multicolour banding (MCB) technique. Our results, and previously published findings, suggest several hotspots for recombination in the pericentromeric heterochromatin of HSA 9. They also demonstrate that constitutional inversions affecting the pericentromeric region of chromosome 9 carry breakpoints located preferentially in 9p12 or 9q13-21.1 and less frequently in 9q12.

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Section: Discussionsupporting

confidence: 81%

“…The cases described by Webb et al 26 show more similarity to cases 50, 51 and 53 of the present study. Interestingly, Webb et al 26 detected an amplification of the 9ph+ region transmitted through all generations. Reddy, 27 Knight et al 28 and Jalal et al 29 all report healthy carriers with a CBG negative 9qh+ variant.…”

Section: Discussionsupporting

confidence: 81%

Homologous sequences at human chromosome 9 bands p12 and q13-21.1 are involved in different patterns of pericentric rearrangements

Starke

Seidel

Henn³

et al. 2002

Eur J Hum Genet

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“…Our results strongly suggest that the bands that have prompted cytogeneticists to describe these euchromatic variants as duplications or triplications of q11.2-q13 are just as spurious as those within HSRs and that the 15q12 band is not included. It is also possible that these variants are in fact constitutional HSRs as suggested by Webb et al (1989) for euchromatic variants of 9p. We are not aware of any evidence that extra NF-1 pseudogene copy number confers any increased risk of NF-1 itself, nor that the mutations which characterise the NF-1 pseudogenes are generally part of the spectrum of mutations found in NF-1 patients (Purandare et al 1995).…”

Section: Discussionmentioning

confidence: 95%

Neurofibromatosis pseudogene amplification underlies euchromatic cytogenetic duplications and triplications of proximal 15q

Barber¹,

Cross²,

Douglas³

et al. 1998

Human Genetics

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Cytogenetically visible interstitial duplications of proximal 15q, which lack the Prader-Willi Angelman critical region (PWACR) frequently segregate in families without phenotypic effect, but the nature of the extra euchromatin has remained unclear. We used comparative genome hybridisation to confirm that the extra material in a cytogenetic triplication originated from proximal 15q. A PAC clone containing sequences specific for the type-1 neurofibromatosis (NF-1) pseudogenes, which map to 15q11.2, hybridised along the length of the enlarged region between the PWACR and the centromere. Computerised measurement of the fluorescent signal from the enlarged and normal chromosomes gave an average ratio of 9.85:1, consistent with amplification. In a second family, an amplified P1-4 signal co-segregated with a cytogenetic duplication and the average ratio between amplified and normal signals in the proband was 8.22:1. Ratios in noncarrier family members and control individuals were close to unity in most cases, but significantly greater than one in at least one instance. Our results provide a novel explanation for cytogenetic variation in 15q11.2. They also suggest that NF-1 pseudogene copy number may be polymorphic in the normal population, and that high copy numbers can produce G bands which do not reflect those of the normal constitutional karyotype.

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“…According to the literature, both variants are considered to have no clinical effects, as they are observed in phenotypically normal persons (Gardner and Sutherland 2004). The first variant has an additional material inserted into the 9p12 band; reported, e.g., by Webb et al (1989). The second one has an extra dark G-band located within the q12 (qh) region (Docherty and Hulten 1993;von Beust and Bink 1999;Ozikinay et al 2005).…”

Section: Euchromatic Variants (Evs)mentioning

confidence: 99%

Chromosome abnormalities without phenotypic consequences

2007

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Some changes in chromosome morphology, detected during cytogenetic analysis, are not associated with clinical defects. Therefore a proper discrimination of harmless variants from true abnormalities, especially during prenatal diagnosis, is crucial to allow precise counseling. In this review we described chromosome variants and examples of chromosome anomalies that are considered to be unrelated to phenotypic consequences. The correlation between the presence of marker chromosomes and a risk of clinical signs is also discussed. Structural rearrangements of heterochromatic material, satellite polymorphism, or fragile sites, are well-known examples of common chromosome variation. However, the absence of clinical effects has also been reported in some cases of chromosome abnormalities concerning euchromatin. Such euchromatic anomalies were divided into 2 categories: unbalanced chromosome abnormalities (UBCAs), such as deletions or duplications, and euchromatic variants (EVs). Recently so-called molecular karyotyping, especially whole-genome screening by the use of high-resolution array-CGH technique, contributed to revealing a high number of previously unknown small genomic variations, which seem to be asymptomatic, as they are present in phenotypically normal individuals.

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Non C-banding variants in some normal families might be homogeneously staining regions

Cited by 24 publications

References 17 publications

Homologous sequences at human chromosome 9 bands p12 and q13-21.1 are involved in different patterns of pericentric rearrangements

Homologous sequences at human chromosome 9 bands p12 and q13-21.1 are involved in different patterns of pericentric rearrangements

Neurofibromatosis pseudogene amplification underlies euchromatic cytogenetic duplications and triplications of proximal 15q

Chromosome abnormalities without phenotypic consequences

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