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Complex small supernumerary marker chromosomes - an update.

Thomas Liehr1, Sanja Cirkovic2, Tanja Lalic2

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Summary
This summary is machine-generated.

Complex small supernumerary marker chromosomes (sSMC) are rare, making up 8.4% of sSMC cases, often linked to Emanuel syndrome. Detailed cytogenetic analysis is crucial for diagnosing these complex sSMC, especially in cases of idiopathic mental retardation.

Keywords:
Complex small supernumerary marker chromosomes (sSMC)Emanuel syndromeGenotype-phenotype correlationMosaicismSSMC shape

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Area of Science:

  • Cytogenetics
  • Human Genetics
  • Molecular Biology

Background:

  • Complex small supernumerary marker chromosomes (sSMC) represent a rare subgroup of sSMC.
  • These chromosomes comprise material from multiple chromosomal origins, with Emanuel syndrome (der(22)t(11;22)) being a well-known example.
  • Previous research suggested complex sSMC might be part of an under-recognized clinical entity.

Purpose of the Study:

  • To summarize and analyze the characteristics of all reported complex sSMC cases.
  • To highlight the prevalence and common features of complex sSMC.
  • To emphasize the diagnostic significance of complex sSMC in genetic disorders.

Main Methods:

  • Compilation and analysis of published data on complex sSMC.
  • Review of cytogenetic findings in patients with complex sSMC.
  • Identification of chromosomal breakpoints and inheritance patterns.

Main Results:

  • A total of 412 complex sSMC cases were summarized, accounting for 8.4% of characterized sSMC.
  • Eighty-two percent of complex sSMC cases are associated with Emanuel syndrome.
  • Other identified complex sSMC syndromes include der(22)t(8;22) and der(13 or 21)t(13 or 21;18).
  • The majority of complex sSMC are centric minutes derived from acrocentric chromosomes, often inherited from balanced translocations and non-mosaic.
  • Specific chromosomal "hot spots" for breakpoints were identified.

Conclusions:

  • Complex sSMC, particularly non-mosaic, centric minute types, require consideration in diagnostic evaluations.
  • Three complex sSMC-associated syndromes are currently identified, with more expected due to characterized recurrent breakpoints.
  • Detailed cytogenetic analysis is vital for diagnosing idiopathic mental retardation, as complex sSMC can be a contributing factor.