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Genetic and Rare Diseases Information Center (GARD)

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Pseudotrisomy 13 syndrome

Other Names for this Disease
  • Holoprosencephaly polydactyly syndrome
  • Pseudo trisomy 13 syndrome
  • Young-Maders syndrome
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What causes trisomy 13?

Almost all cases of trisomy 13 are caused by random events during the formation of an egg or sperm in healthy parents.  Most often, the error occurs during cell division when a pair of chromosomes 13 stick together in one cell instead of separating into two cells (this is called nondisjunction); this produces an egg or sperm cell (reproductive cells) with an extra copy of chromosome 13.  If one of these reproductive cells with an extra copy of chromosome 13 contributes to the genetic makeup of a child, the child will have an extra chromosome 13 in each cell of the body and have trisomy 13.

Translocation trisomy 13 occurs when a child inherits an extra chromosome 13 that is attached to another chromosome.  A parent with normal chromosomes can have a rearrangement of genetic material between chromosome 13 and another chromosome such that the two chromosome become attached to each other. These rearrangements are called balanced translocations because there is no extra material from chromosome 13. A person with a balanced translocation involving chromosome 13 has an increased chance of having a child with trisomy 13, because they may pass on the chromosome that is abnormally attached to chromosome 13, resulting in the child having extra chromosome material.[1]
Last updated: 4/16/2012

  1. Trisomy 13. Genetics Home Reference. January 2009; Accessed 1/9/2012.