Small supernumerary marker chromosome

From Embryology


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Some Recent Findings

  • Small supernumerary marker chromosome 15 and a ring chromosome 15 associated with a 15q26.3 deletion excluding the IGF1R gene[1] "Array comparative genomic hybridization is essential in the investigation of chromosomal rearrangements associated with epilepsy, intellectual disability, and dysmorphic features. In many cases deletions, duplications, additional marker chromosomes, and ring chromosomes originating from chromosome 15 lead to abnormal phenotypes. We present a child with epilepsy, cardiac symptoms, severely delayed mental and growth development, behavioral disturbances and characteristic dysmorphic features showing a ring chromosome 15 and a small supernumerary marker chromosome. Array CGH detected a 1 Mb deletion of 15q26.3 in a ring chromosome 15 and a 2.6 Mb copy number gain of 15q11.2 corresponding to a small supernumerary marker chromosome involving proximal 15q. Our findings add to previously published results of 15q11q13 duplications and 15q26 terminal deletions. Based on our study we can support the previous reported limited information about the role of SELS, SNRPA1, and PCSK6 genes in the development of the heart morphology. On the other hand, we found that the copy number loss of our patient did not involve the IGF1R gene which is often associated with growth retardation (short stature and decreased weight). We hypothesize that haploinsufficiency of the 15q26 genomic region distal to IGF1R gene might be related to growth disturbance; however, presence of the ring chromosome 15 itself could also be responsible for the growth delay."

Small supernumerary marker chromosomes and uniparental disomy have a story to tell[2]

"Small supernumerary maker chromosomes (sSMC) and uniparental disomy (UPD) are rare, and a combination of both is rarely encountered. Accordingly, only 46 sSMC cases UPD have been reported. Despite of its rareness, UPD has to be considered, especially in prenatal cases with sSMC. Here, the authors reviewed all sSMC cases with UPD (sSMC(U+)) and compared them to sSMC without UPD (sSMC(U-)), which resulted in the following correlations: 1) every sSMC, irrespective of its chromosomal origin, may be principally connected with UPD; 2) mixed hetero- and iso-UPD (hUPD/iUPD) can be observed most often in sSMC(U+) cases followed by complete iUPD, complete hUPD, and segmental iUPD; 3) UPD of chromosomes 6, 7, 14, 15, 16, and 20 is most often reported in sSMC(U+); 4) maternal UPD was approximately nine times more frequent than paternal UPD; 5) if mosaic with a normal cell line, acrocentric-derived sSMC had a three times higher chance of occurrence than the corresponding nonmosaic sSMC cases; 6) UPD in connection with a parentally inherited sSMC is, if existent at all, a rare event; and 7) the gender type and shape of sSMC had no effect on UPD formation. Overall, sSMC(U+) cases may have a story to tell about chromosome number control mechanisms in early embryogenesis."

Handling small supernumerary marker chromosomes in prenatal diagnostics[3]

"Small supernumerary marker chromosomes (sSMCs) are structurally abnormal chromosomes that cannot be thoroughly characterized by conventional banding cytogenetics and are equal in size or smaller than chromosome 20. They are present in 0.075% of prenatal cases and, overall, approximately 3 million people worldwide are carriers of a sSMC. In prenatal cases with ultrasound abnormalities, sSMCs are found in up to approximately 0.2% of the cases. First described in 1961, it is now known that sSMCs have no phenotypic effects in approximately 70% of de novo cases. Nonetheless, in at least 30-50% of prenatally detected sSMC cases, the pregnancy is terminated; that is, for a certain percentage of potentially healthy children with a sSMC, an abortion is induced. This situation can only be improved by providing increased amounts of and more reliable information on sSMCs. This article provides an overview on current state-of-the-art technologies and how sSMC analysis can be optimized in prenatal diagnostics."

Frequency of small supernumerary marker chromosomes in prenatal, newborn, developmentally retarded and infertility diagnostics[4]

"In this study the substantial and in part contradictory data available in the literature was collected concerning the frequency of small supernumerary marker chromosomes (sSMC) in the human population in general, and in special subpopulations. One hundred and thirty-two studies on sSMC were reviewed. In summary 1,288,693 cytogenetically studied cases detecting 980 sSMC were compiled. In 132 international surveys there were no ethnic effects detected in the sSMC frequency. sSMC were present in 0.075% of unselected prenatal cases but only in 0.044% of consecutively studied postnatal ones. In infertile subjects, 0.125% were sSMC carriers, distinguishing male from female subjects by a 7.5:1 difference in sSMC frequency for this special group. In developmentally retarded patients the sSMC rate was elevated to 0.288%, similar to prenatal cases with ultrasound abnormalities (0.204%). No increased risk for the presence of sSMC was detected in ICSI-induced pregnancies. Worldwide there are approximately 2.7 x 10(6) living sSMC carriers; 1.8 x 10(6) have a de novo sSMC and approximately 70% of those are clinically normal. Strikingly, 30-50% of pregnancies diagnosed with an sSMC fetus are terminated. This may be connected with the empirical risk that approximately 30% of sSMC carriers manifest clinical abnormalities. Thus, in summary there is a strong need for a better genotype-phenotype correlation enabling better genetic counseling."

Small supernumerary marker chromosomes (sSMC) in humans[5]

"Small supernumerary marker chromosomes (sSMC), defined as additional centric chromosome fragments too small to be identified or characterized unambiguously by banding cytogenetics alone, are present in 0.043% of newborn children. Several attempts have been made to correlate certain sSMC with a specific clinical picture, resulting in the description of several syndromes such as the i(18p)-, der(22)-, i(12p)- (Pallister Killian syndrome) and inv dup(22)- (cat-eye) syndromes. However, most of the remaining sSMC including minute-, ring-, inverted-duplication- as well as complex-rearranged chromosomes, have not yet been correlated with clinical syndromes, mostly due to problems in their comprehensive characterization. Here we present an overview of sSMC, including the first attempt to address problems of nomenclature and their modes of formation, problems connected with mosaicism plus familial occurrence. The review also discusses the frequency of sSMC in prenatal, postnatal, and clinical cases, their chromosomal origin and their association with uniparental disomy. A short review of the up-to-date approaches available for sSMC characterization is included. Clinically relevant correlations concerning the presence of a specific sSMC and its phenotypic consequences should become available soon."


  1. Szabó A, Czakó M, Hadzsiev K, Duga B, Bánfai Z, Komlósi K & Melegh B. (2018). Small supernumerary marker chromosome 15 and a ring chromosome 15 associated with a 15q26.3 deletion excluding the IGF1R gene. Am. J. Med. Genet. A , 176, 443-449. PMID: 29226546 DOI.
  2. Liehr T, Ewers E, Hamid AB, Kosyakova N, Voigt M, Weise A & Manvelyan M. (2011). Small supernumerary marker chromosomes and uniparental disomy have a story to tell. J. Histochem. Cytochem. , 59, 842-8. PMID: 21673185 DOI.
  3. Liehr T, Ewers E, Kosyakova N, Klaschka V, Rietz F, Wagner R & Weise A. (2009). Handling small supernumerary marker chromosomes in prenatal diagnostics. Expert Rev. Mol. Diagn. , 9, 317-24. PMID: 19435454 DOI.
  4. Liehr T & Weise A. (2007). Frequency of small supernumerary marker chromosomes in prenatal, newborn, developmentally retarded and infertility diagnostics. Int. J. Mol. Med. , 19, 719-31. PMID: 17390076
  5. Liehr T, Claussen U & Starke H. (2004). Small supernumerary marker chromosomes (sSMC) in humans. Cytogenet. Genome Res. , 107, 55-67. PMID: 15305057 DOI.

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Idiogram Chromosome Banding - The term refers to the light and dark pattern, seen after staining with a dye, of individual chromosomes identified in metaphase. It is only in meiosis and mitosis during metaphase that chromosomes can be easily identified, during the normal cell life (interphase) the chromosomes are unravelled and distributed within the nucleus in chromosome territories. A band is that part of a chromosome which is clearly distinguishable from nearby regions by appearing darker or brighter with one or more banding techniques.
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Inheritance Pattern images: Genetic Abnormalities | autosomal dominant | autosomal recessive | X-linked dominant (affected father) | X-Linked dominant (affected mother) | X-Linked recessive (affected father) | X-Linked recessive (carrier mother) | mitochondrial inheritance | Codominant inheritance | Genogram symbols | Genetics
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Cite this page: Hill, M.A. (2019, June 26) Embryology Small supernumerary marker chromosome. Retrieved from

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G