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

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 Bchromosomes 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.

A case of an infertile male with a small supernumerary marker chromosome negative for M-FISH and containing only heterochromatin

“…It supposed that the sSMC might represent a multifold amplification of a very small region of the genome, analogously to that have been seen in homologously staining regions (HSRs) and double minutes (DMs) described in some types of tumour cells [7][8][9][10]. Liehr T et al have reported a patient from whom the similar results were obtained [11].They suggested that a minority of sSMC show similarities to B-chromosomes.…”

Impaired Spermatogenesis due to Small Supernumerary Marker Chromosomes: The Reason for Infertility Is Only Reliably Ascertainable by Cytogenetics

“…Thus, the presence of an sSMC does not cause reproductive problems in all carriers. However, as sSMC and B chromosomes show some similarities, it has been suggested that it may be an evolutionary mechanism which can be observed in infertile males, i.e., genetic drift by which nature tries to get rid of the otherwise harmless sSMC via the male germline [Liehr et al, 2008].…”

Small Supernumerary Marker Chromosomes and Uniparental Disomy Have a Story to Tell

“…In general, sSMC can be derived from each of the 24 human chromosomes, although sSMC with no chromosomal origin determined have also been reported (Mackie Ogilvie et al 2001;Liehr et al 2008). Also, UPD can in principal appear for all human chromosomes (Liehr et al 2004;Rodríguez-Santiago et al 2010;Liehr 2011aLiehr , 2011b.…”