Research

Small supernumerary marker chromosomes (sSMC) in humans; are there B chromosomes hidden among them

Thomas Liehr¹ , Kristin Mrasek¹ , Nadezda Kosyakova^1,2 , Caroline Mackie Ogilvie³ , Joris Vermeesch⁴ , Vladimir Trifonov^5,6 and Nikolai Rubtsov⁶

¹Institute of Human Genetics and Anthropology, Kollegiengasse 10, D-07743 Jena, Germany

²Research Centre for Medical Genetics, Russian Academy of Medical Sciences, Moskvorechie Str. 1, Moscow 115478, Russian Federation

³Division of Medical and Molecular Genetics, King's, Guy's and St. Thomas' Medical School, London, UK

⁴Center for Human Genetics, University Hospital Leuven, Herestraat 49, B-3000 Leuven, Belgium

⁵Department of Clinical Veterinary Medicine, Madingley Road, CB3 OES Cambridge, UK

⁶Institute of Cytology and Genetics, Lavrentev Str. 10, 630090 Novosibirsk, Russia

author email corresponding author email

Molecular Cytogenetics 2008, 1:12doi:10.1186/1755-8166-1-12

Published:	4 June 2008

Abstract

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.