Marker chromosome

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Karyotype of a tumor cell line stained with G-banding. Instead of the normal 46 chromosomes, there are 57 here. In addition to many other chromosome aberrations , a marker chromosome can be seen in the box at the top.
Classification according to ICD-10
Q92.6 Extra marker chromosomes
ICD-10 online (WHO version 2019)

Marker chromosomes are small chromosomes that can appear alongside normal chromosomes in an individual. In 1995, the International System for Human Cytogenetics defined a marker chromosome as an abnormal chromosome in which no part can be identified. The identification that was not possible related to the technique of G-banding , with which larger sections of normal chromosomes can be clearly identified (see also figure). This is not possible with marker chromosomes, usually due to their small size. Today, however, characterization is possible, for example, with high-resolution fluorescence in situ hybridization . Marker chromosomes that are smaller than human chromosome 20 are also known as small supernumerary marker chromosomes or with the corresponding English abbreviation sSMC (for: small supernumerary marker chromosomes).

Marker chromosomes contain a centromere and are therefore normally passed on to daughter cells during cell division ( mitosis ). Marker chromosomes can also have the shape of a ring chromosome . In contrast to B chromosomes , which have developed active mechanisms to accumulate in the germline , marker chromosomes are passed on to the offspring in a random pattern. While B chromosomes do not occur in humans, marker chromosomes have been described in a number of cases. The rate of occurrence of marker chromosomes in newborns is given as 0.043%. This results in estimates of 2.5 million people worldwide and 35,000 affected people in Germany. Human marker chromosomes can arise from any of the 24 human chromosomes. Around 60% of cases are new, 40% are inherited in families. Marker chromosomes can also occur in tumor cells (see figure).

Clinical significance

Whether a marker chromosome is of clinical importance depends on whether and, if so, which chromosomal genes it contains, and whether the presence of the marker chromosomes results in an imbalance in these genes. A partial trisomy , i.e. a partial triple presence of chromosomal segments instead of the normal double execution, comes into question here . The chromosomal origin and thus the genetic composition of the marker chromosome is important, but also whether other molecular genetic abnormalities occur in parallel, e.g. B. Uniparental disomy .

About 70% of people with an sSMC are clinically normal, 30% are clinically abnormal to varying degrees. Clinical abnormalities range from slight physical abnormalities or disabilities, mild intellectual disabilities to severe physical limitations / disabilities with or without mental and / or psychological disabilities / abnormalities, e.g. B. Autism . Marker chromosomes made from chromosome 15 material are the most common, accounting for around 30%. Isochromosomes of the short arm of chromosome 12 , the Pallister-Killian syndrome, follow with 11% . The cat-eye syndrome is another example.

The diagnosis of a marker chromosome is particularly problematic in prenatal diagnosis in newly emerging cases. Until recently, the statement about the possible clinical effects of the sSMC was also rather imprecise. Research on the genotype - phenotype correlation of the sSMC is currently in progress.

In the shorthand cytogenetic notation, marker chromosomes are referred to as mar . While a man with the normal 46 chromosomes (without marker chromosomes) is noted as 46, XY, a male karyotype with a marker chromosome is written as 47, XY, + mar, and a female karyotype as 47, XX, + mar.

literature

Individual evidence

  1. Alphabetical index for the ICD-10-WHO version 2019, volume 3. German Institute for Medical Documentation and Information (DIMDI), Cologne, 2019, p. 540
  2. Definition according to the glossary of the Gene Tests website ( Memento from December 19, 2009 in the Internet Archive ), University of Washington and Children's Health System, Seattle
  3. F. Mitelman (Ed.): ISCN 1995: An International System for Human Cytogenetic Nomenclature. S. Karger, Basel 1995.
  4. L. Brecevic, S. Michel, H. Starke, K. Müller, N. Kosyakova, K. Mrasek, A. Weise, T. Liehr: Multicolor FISH used for the characterization of small supernumerary marker chromosomes (sSMC) in commercially available immortalized cell lines. In: Cytogenetic & Genome Research. 2006, Vol. 114 Issue 3/4, pp. 319-324. doi: 10.1159 / 000094220
  5. a b c d e T. Liehr, U. Claussen, H. Starke: Small supernumerary marker chromosomes (sSMC) in humans. In: Cytogenet Genome Research. 2004; 107, pp. 55-67. doi: 10.1159 / 000079572 .
  6. ^ Jan Murken, Tiemo Grimm, Elke Holinski-Feder: Pocket textbook human genetics. 7th edition. Thieme, Stuttgart 2006, ISBN 3-13-139297-5 .
  7. T. Liehr, K. Mrasek, A. Weise, A. Dufke, L. Rodríguez, Guardia N. Martínez, A. Sanchís, JR Vermeesch, C. Rame, A. Polityko, OA Haas, J. Anderson, U. Claussen, F. von Eggeling, H. Starke: Small supernumerary marker chromosomes - progress towards a genotype-phenotype correlation. In: Cytogenetic & Genome Research. 2006, Vol. 112 Issue 1/2, pp. 23-34. doi: 10.1159 / 000087510

Web links

  • Report on small surplus marker chromosomes in the Uni-Journal Jena (online) .
  • English-language information page about surplus small marker chromosomes from a research group at the University of Jena (online) .
  • Report on a contagious tumor with marker chromosomes in the Tasmanian devil in the journal Telepolis (online) .