Research
Small supernumerary marker chromosomes (sSMC) in humans; are there B chromosomes hidden among them
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* Corresponding author: Thomas Liehr i8lith@mti.uni-jena.de
1 Institute of Human Genetics and Anthropology, Kollegiengasse 10, D-07743 Jena, Germany
2 Research Centre for Medical Genetics, Russian Academy of Medical Sciences, Moskvorechie Str. 1, Moscow 115478, Russian Federation
3 Division of Medical and Molecular Genetics, King's, Guy's and St. Thomas' Medical School, London, UK
4 Center for Human Genetics, University Hospital Leuven, Herestraat 49, B-3000 Leuven, Belgium
5 Department of Clinical Veterinary Medicine, Madingley Road, CB3 OES Cambridge, UK
6 Institute of Cytology and Genetics, Lavrentev Str. 10, 630090 Novosibirsk, Russia
Molecular Cytogenetics 2008, 1:12 doi:10.1186/1755-8166-1-12
Published: 4 June 2008Abstract
Background
Small supernumerary marker chromosomes (sSMC) and B-chromosomes represent a heterogeneous collection of chromosomes added to the typical karyotype, and which are both small in size. They may consist of heterochromatic and/or euchromatic material. Also a predominance of maternal transmission was reported for both groups. Even though sSMC and B-chromosomes show some similarity it is still an open question if B-chromosomes are present among the heterogeneous group of sSMC. According to current theories, sSMC would need drive, drift or beneficial effects to increase in frequency in order to become B chromosome. However, up to now no B-chromosomes were described in human.
Results
Here we provide first evidence and discuss, that among sSMC B-chromosomes might be hidden. We present two potential candidates which may already be, or may in future evolve into B chromosomes in human: (i) sSMC cases where the marker is stainable only by DNA derived from itself; and (ii) acrocentric-derived inverted duplication sSMC without associated clinical phenotype. Here we report on the second sSMC stainable exclusively by its own DNA and show that for acrocentric derived sSMC 3.9× more are familial cases than reported for other sSMC.
Conclusion
The majority of sSMC are not to be considered as B-chromosomes. Nonetheless, a minority of sSMC show similarities to B-chromosomes. Further studies are necessary to come to final conclusions for that problem.