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Pallister-Killian mosaic syndrome

Other Names for this Disease
  • Chromosome 12, Isochromosome 12p syndrome
  • Killian syndrome
  • Killian Teschler-Nicola syndrome
  • Pallister Killian syndrome
  • Pallister mosaic syndrome
More Names
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Pallister-Killian mosaic syndrome is a disorder that is characterized by extremely weak muscle tone (hypotonia) in infancy and early childhood, intellectual disability, distinctive facial features, sparse hair, areas of unusual skin coloring (pigmentation), and other birth defects. The signs and symptoms of the Pallister-Killian mosaic syndrome can vary, although most documented cases of people with the syndrome have severe to profound intellectual disability and other serious health problems.[1]

Pallister-Killian mosaic syndrome is usually caused by the presence of an abnormal extra chromosome 12 called isochromosome 12p. Normal chromosomes have one long (q) arm and one short (p) arm, but isochromosomes have either two q arms or two p arms. Isochromosome 12p is a version of chromosome 12 made up of two p arms. Cells normally have two copies of each chromosome, one inherited from each parent. In people with Pallister-Killian mosaic syndrome, cells have the two usual copies of chromosome 12, but some cells also have the isochromosome 12p. These cells have a total of four copies of all the genes on the p arm of chromosome 12. The extra genetic material from the isochromosome disrupts the normal course of development, causing the characteristic features of this disorder.[1]

Although Pallister-Killian mosaic syndrome is usually caused by an isochromosome 12p, other, more complex chromosomal changes involving chromosome 12 are responsible for the disorder in rare cases.[1]
Last updated: 9/11/2009


  1. Pallister-Killian mosaic syndrome. Genetics Home Reference. June 2009; Accessed 9/11/2009.
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Basic Information

  • Genetics Home Reference (GHR) contains information on Pallister-Killian mosaic syndrome. This website is maintained by the National Library of Medicine.
  • The National Organization for Rare Disorders (NORD) is a federation of more than 130 nonprofit voluntary health organizations serving people with rare disorders. Click on the link to view information on this topic.

In Depth Information

  • The Online Mendelian Inheritance in Man (OMIM) is an catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs.  Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Pallister-Killian mosaic syndrome. Click on the link to view a sample search on this topic.