title: Somatic mosaicism in cases with small supernumerary marker chromosomes.
abstract: Somatic mosaicism is something that is observed in everyday lives of cytogeneticists. Chromosome instability is one of the leading causes of large-scale genome variation analyzable since the correct human chromosome number was established in 1956. Somatic mosaicism is also a well-known fact to be present in cases with small supernumerary marker chromosomes (sSMC), i.e. karyotypes of 47,+mar/46. In this study, the data available in the literature were collected concerning the frequency mosaicism in different subgroups of patients with sSMC. Of 3124 cases with sSMC 1626 (52%) present with somatic mosaicism. Some groups like patients with Emanuel-, cat-eye- or i(18p)- syndrome only tend rarely to develop mosaicism, while in Pallister-Killian syndrome every patient is mosaic. In general, acrocentric and non-acrocentric derived sSMCs are differently susceptible to mosaicism; non-acrocentric derived ones are hereby the less stable ones. Even though, in the overwhelming majority of the cases, somatic mosaicism does not have any detectable clinical effects, there are rare cases with altered clinical outcomes due to mosaicism. This is extremely important for prenatal genetic counseling. Overall, as mosaicism is something to be considered in at least every second sSMC case, array-CGH studies cannot be offered as a screening test to reliably detect this kind of chromosomal aberration, as low level mosaic cases and cryptic mosaics are missed by that.
authors.affiliation: Jena University Hospital, Institute of Human Genetics and Anthropology, Jena, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Liehr
authors.forename: Tatyana
authors.initials: T
authors.lastname: Karamysheva
authors.forename: Martina
authors.initials: M
authors.lastname: Merkas
authors.forename: Lukrecija
authors.initials: L
authors.lastname: Brecevic
authors.forename: Ahmed B
authors.initials: AB
authors.lastname: Hamid
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Ewers
authors.forename: Kristin
authors.initials: K
authors.lastname: Mrasek
authors.forename: Nadezda
authors.initials: N
authors.lastname: Kosyakova
authors.forename: Anja
authors.initials: A
authors.lastname: Weise