title: Complex small supernumerary marker chromosomes - an update.
abstract: BACKGROUND
  Complex small supernumerary marker chromosomes (sSMC) constitute one of the smallest subgroups of sSMC in general. Complex sSMC consist of chromosomal material derived from more than one chromosome; the best known representative of this group is the derivative chromosome 22 {der(22)t(11;22)} or Emanuel syndrome. In 2008 we speculated that complex sSMC could be part of an underestimated entity.
  
  
  RESULTS
  Here, the overall yet reported 412 complex sSMC are summarized. They constitute 8.4% of all yet in detail characterized sSMC cases. The majority of the complex sSMC is contributed by patients suffering from Emanuel syndrome (82%). Besides there are a der(22)t(8;22)(q24.1;q11.1) and a der(13)t(13;18)(q11;p11.21) or der(21)t(18;21)(p11.21;q11.1) = der(13 or 21)t(13 or 21;18) syndrome. The latter two represent another 2.6% and 2.2% of the complex sSMC-cases, respectively. The large majority of complex sSMC has a centric minute shape and derives from an acrocentric chromosome. Nonetheless, complex sSMC can involve material from each chromosomal origin. Most complex sSMC are inherited form a balanced translocation in one parent and are non-mosaic. Interestingly, there are hot spots for the chromosomal breakpoints involved.
  
  
  CONCLUSIONS
  Complex sSMC need to be considered in diagnostics, especially in non-mosaic, centric minute shaped sSMC. As yet three complex-sSMC-associated syndromes are identified. As recurrent breakpoints in the complex sSMC were characterized, it is to be expected that more syndromes are identified in this subgroup of sSMC. Overall, complex sSMC emphasize once more the importance of detailed cytogenetic analyses, especially in patients with idiopathic mental retardation.
authors.affiliation: Jena University Hospital, Friedrich Schiller University, Institute of Human Genetics, Kollegiengasse 10, Jena D-07743, Germany ; Institut für Humangenetik, Postfach, Jena D-07740, Germany.
authors.forename: Thomas
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authors.lastname: Liehr
authors.affiliation: Laboratory for Medical Genetics, Mother and Child Health Care Institute of Serbia "Dr Vukan Cupic", Radoje Dakic str. 6-8, Belgrade 11070, Serbia.
authors.forename: Sanja
authors.initials: S
authors.lastname: Cirkovic
authors.affiliation: Laboratory for Medical Genetics, Mother and Child Health Care Institute of Serbia "Dr Vukan Cupic", Radoje Dakic str. 6-8, Belgrade 11070, Serbia.
authors.forename: Tanja
authors.initials: T
authors.lastname: Lalic
authors.affiliation: Laboratory for Medical Genetics, Mother and Child Health Care Institute of Serbia "Dr Vukan Cupic", Radoje Dakic str. 6-8, Belgrade 11070, Serbia ; University of Belgrade, Faculty of Biology, Belgrade, Serbia.
authors.forename: Marija
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authors.lastname: Guc-Scekic
authors.affiliation: Military Hospital associated with "Universidad de la República (UDELAR)", Montevideo, Uruguay.
authors.forename: Cynthia
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authors.lastname: de Almeida
authors.affiliation: Department of Gynecology and Obstetrics, UKSH Campus Kiel, Arnold-Heller-Str. 3; House 24, Kiel 24105, Germany.
authors.forename: Jörg
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authors.lastname: Weimer
authors.affiliation: Research Center for Mental Health, RAMS, Moscow, Russia ; Institute of Pediatrics and Children Surgery, RF Ministry of Health, Moscow, Russia.
authors.forename: Ivan
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authors.lastname: Iourov
authors.affiliation: Department of Morphology and Genetics, Universidade Federal de São Paulo, Rua Botucatu 740, São Paulo SP, 04023-900, Brazil.
authors.forename: Maria Isabel
authors.initials: MI
authors.lastname: Melaragno
authors.affiliation: Department of Morphology and Genetics, Universidade Federal de São Paulo, Rua Botucatu 740, São Paulo SP, 04023-900, Brazil.
authors.forename: Roberta S
authors.initials: RS
authors.lastname: Guilherme
authors.affiliation: Department of Pediatrics, Laboratory of Medical Genetics, University General Hospital of Patras, Rion, Patras 26504, Greece.
authors.forename: Eunice-Georgia G
authors.initials: EG
authors.lastname: Stefanou
authors.affiliation: Hacettepe University School of Medicine, Dept of Medical Genetics, 06100 Sihhiye, Ankara, Turkey.
authors.forename: Dilek
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authors.lastname: Aktas
authors.affiliation: Jena University Hospital, Friedrich Schiller University, Institute of Human Genetics, Kollegiengasse 10, Jena D-07743, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Kreskowski
authors.affiliation: Jena University Hospital, Friedrich Schiller University, Institute of Human Genetics, Kollegiengasse 10, Jena D-07743, Germany.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Klein
authors.affiliation: Jena University Hospital, Friedrich Schiller University, Institute of Human Genetics, Kollegiengasse 10, Jena D-07743, Germany.
authors.forename: Monika
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authors.lastname: Ziegler
authors.affiliation: Jena University Hospital, Friedrich Schiller University, Institute of Human Genetics, Kollegiengasse 10, Jena D-07743, Germany.
authors.forename: Nadezda
authors.initials: N
authors.lastname: Kosyakova
authors.affiliation: Institut für Humangenetik, Universitätsklinikum, Leipziger Str. 44, Magdeburg 39120, Germany.
authors.forename: Marianne
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authors.lastname: Volleth
authors.affiliation: Jena University Hospital, Friedrich Schiller University, Institute of Human Genetics, Kollegiengasse 10, Jena D-07743, Germany.
authors.forename: Ahmed B
authors.initials: AB
authors.lastname: Hamid
keywords: Complex small supernumerary marker chromosomes (sSMC); Emanuel syndrome; Genotype-phenotype correlation; Mosaicism; SSMC shape