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Abstract
BackgroundMarker chromosomes are small supernumerary chromosomes that cannot be unambiguously identified by chromosome banding techniques alone. However, the precise characterization of marker chromosomes is important for prenatal diagnosis and proper genetic counseling. In this study, we evaluated the chromosomal origin of marker chromosomes using a combination of banding cytogenetics and molecular cytogenetic techniques including diverse fluorescence in situ hybridization (FISH) assays and array comparative genomic hybridization (array CGH).ResultsIn a series of 2871 patients for whom cytogenetic analysis was requested, 14 cases with small supernumerary marker chromosomes (sSMCs) were identified. Nine sSMCs were mosaic, and five nonmosaic. Of the nine cases with known parental origins, four were identified as de novo, and four and one were maternally and paternally inherited, respectively. Six sSMCs were identified by FISH using centromeric probes; three sSMCs were derived from chromosome 15, including two heterochromatic sSMC(15)s and a large sSMC(15) spanning 15q11.1q13.1, and three sSMCs originated from chromosome 14 or 22. Array CGH revealed two cases with derivatives of chromosome 2 and whole chromosome painting multicolor-FISH (M-FISH) identified three cases with derivatives of chromosome 6, 16, and 19, respectively. One maker chromosome in Turner syndrome was characterized as sSMC(X) by preferential application of a centromeric probe for X-chromosome. In addition, one sSMC composed of genomic materials from chromosomes 12 and 18 was identified in parallel with parental karyotype analysis that revealed the reciprocal balanced translocation.ConclusionsThis report is the largest study on sSMCs in Korea and expands the spectrum of sSMCs that are molecularly characterized.Electronic supplementary materialThe online version of this article (doi:10.1186/s13039-016-0273-5) contains supplementary material, which is available to authorized users.
Highlights
Marker chromosomes are small supernumerary chromosomes that cannot be unambiguously identified by chromosome banding techniques alone
There has been a previous report on marker chromosomes identified in Korean patients [5] investigated with fluorescence in situ hybridization (FISH) analysis, but with advancements in molecular cytogenetic diagnostics, tools including whole-chromosome painting FISH and array comparative genomic hybridization have been applied in characterization of marker chromosomes
Of 2871 patients referred for chromosomal analysis, marker chromosomes were identified in 14 patients
Summary
Marker chromosomes are small supernumerary chromosomes that cannot be unambiguously identified by chromosome banding techniques alone. We evaluated the chromosomal origin of marker chromosomes using a combination of banding cytogenetics and molecular cytogenetic techniques including diverse fluorescence in situ hybridization (FISH) assays and array comparative genomic hybridization (array CGH). Known as small supernumerary marker chromosomes (sSMCs), are structurally abnormal chromosomes that cannot be unambiguously identified or characterized by conventional banding cytogenetics (ISCN 2013) [1] They are generally equal or smaller in size than a chromosome 20 of the same metaphase spread [2], and the According to a recent, comprehensive review [3], marker chromosomes are found in 0.075 % of unselected prenatal cases, and in 0.044 % of consecutive postnatal cases, but frequencies are elevated to 0.125 % in infertile subjects and to 0.255 % in developmentally retarded patients [3]. There has been a previous report on marker chromosomes identified in Korean patients [5] investigated with fluorescence in situ hybridization (FISH) analysis, but with advancements in molecular cytogenetic diagnostics, tools including whole-chromosome painting FISH and array comparative genomic hybridization (array CGH) have been applied in characterization of marker chromosomes.
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