Abstract
BackgroundSmall supernumerary marker chromosomes (sSMC) are present ~2.6 × 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.ResultsHere 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.ConclusionMore 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.
Highlights
Small supernumerary marker chromosomes are present ~2.6 × 106 human worldwide. sSMC are a heterogeneous group of derivative chromosomes concerning their clinical consequences as well as their chromosomal origin and shape
The third case reported here (Case C) is a child with a cat eye syndrome which is carrier of a dicentric sSMC leading to a partial tetrasomy of 22q11.21
Among ~2500 reported sSMC cases studied for their chromosomal origin and subsequently reported, 22 cases with unique complex sSMC were detected [10]
Summary
Small supernumerary marker chromosomes (sSMC) are present ~2.6 × 106 human worldwide. sSMC are a heterogeneous group of derivative chromosomes concerning their clinical consequences as well as their chromosomal origin and shape. Small supernumerary marker chromosomes (sSMC) are present ~2.6 × 106 human worldwide. Small supernumerary marker chromosomes (sSMC) are a major problem in cytogenetic diagnostics and genetic counseling. Molecular Cytogenetics 2008, 1:6 http://www.molecularcytogenetics.org/content/1/1/6 ticularly those that are prenatally ascertained, are not easy to correlate with a clinical outcome [2]. The risk for an abnormal phenotype in prenatally ascertained de novo cases with sSMC is considered to be ~13% [3]. This has been refined to 7% (for sSMC from chromosome 13, 14, 21 or 22) and 28% (for all nonacrocentric autosomes) [4] and has been suggested to be 30% [5]. SSMC transmitted by normal sSMC carriers to their progeny are not correlated with clinical problems [6], exceptions have been described [7]
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