engleski

MOLECULAR CYTOGENETIC CHARACTERIZATION OF SMALL SUPERNUMERARY MARKER CHROMOSOMES (sSMC)

By definition small supernumerary marker chromosomes (sSMC) are structurally abnormal chromosomes which are too small to be characterized by banding techniques alone ; and are equal or smaller than chromosome 20 of the same metaphase spread. For their identification and precise delineation molecular cytogenetics is required. As to their origin, about one third are derived from chromosome 15 ; one third produces four specific clinical phenotypes: Pallister-Killian syndrome, der(22)-, inv dup (22)/cat-eye syndrome, and i(18p)-syndrome ; and one third of small markers have not yet been correlated with clinical syndromes. When during the cytogenetic analysis a small marker chromosome is found, problems from the clinical side arise, because often there is an indistinct phenotype, the breakpoints on both arms are variable, and usually there are no familial cases available for reference. Furthermore, if marker is found at prenatal diagnosis, there is very limited time for workup and it is not easy to predict the clinical outcome. An additional problem is that the phenotype might be partially due to uniparental disomy. The ideal methods for identification of such small markers are M-FISH, reverse painting and aCGH. In this context an approach for the straightforward, precise and reliable characterization of sSMCs developed by Jena's group, includes cenM-FISH for the identification of the marker origin, followed by subcenM-FISH and MCB for the breakpoints characterization. The power of this comprehensive approach is demonstrated in the study of 14 sSMC cell lines obtained from the ECACC, and an overview of sSMC in humans is addressed in addition.

small supernumerary marker chromosomes; sSMC; cell lines; molecular cytogenetics

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