title: Complex rearranged small supernumerary marker chromosomes (sSMC), three new cases; evidence for an underestimated entity?
abstract: BACKGROUND
  Small supernumerary marker chromosomes (sSMC) are present ~2.6 x 106 human worldwide. sSMC are a heterogeneous group of derivative chromosomes concerning their clinical consequences as well as their chromosomal origin and shape. Besides the sSMC present in Emanuel syndrome, i.e. der(22)t(11;22)(q23;q11), only few so-called complex sSMC are reported.
  
  
  RESULTS
  Here we report three new cases of unique complex sSMC. One was a de novo case with a dic(13 or 21;22) and two were maternally derived: a der(18)t(8;18) and a der(13 or 21)t(13 or 21;18). Thus, in summary, now 22 cases of unique complex sSMC are available in the literature. However, this special kind of sSMC might be under-diagnosed among sSMC-carriers.
  
  
  CONCLUSIONS
  More comprehensive characterization of sSMC and approaches like reverse fluorescence in situ hybridization (FISH) or array based comparative genomic hybridization (array-CGH) might identify them to be more frequent than only ~0.9% among all sSMC.
authors.affiliation: Institut für Humangenetik und Anthropologie, Kollegiengasse 10, D-07743 Jena, Germany. i8lith@mti.uni-jena.de.
authors.forename: Vladimir
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authors.lastname: Liehr