Small supernumerary marker chromosomes (sSMC) in humans; are there B chromosomes hidden among them
Liehr, Thomas × Mrasek, Kristin Kosyakova, Nadezda Ogilvie, Caroline Mackie Vermeesch, Joris Trifonov, Vladimir Rubtsov, Nikolai #
BioMed Central Ltd
Molecular Cytogenetics vol:1 issue:1
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 3.9x 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.