from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The condition of having three copies of a given chromosome in each somatic cell rather than the normal number of two.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The presence of three copies, instead of the normal two, of a particular chromosome of in an organism.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. chrosomal abnormality in which there is one more than the normal number of chromosomes in a cell


tri- + -som(e)3 + -y2.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From trisome +‎ -y. (Wiktionary)


  • The doctors soon discovered that he had multiple physical problems due to a genetic condition called trisomy 18.

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  • The baby had a serious chromosomal problem called trisomy 18, and Helen had to terminate the pregnancy.

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  • ROWLAND: Sam Strickland (ph) and Mandy Lemky's (ph) son was born with a deadly chromosomal disorder, known as trisomy 18, instead of two chromosome 18s, he had three.

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  • Bella Santorum was born with a genetic disorder called trisomy 18 - or Edwards syndrome - which results in severe disabilities and abnormalities. | Top Stories

  • Bella Santorum, 3, suffers from a rare and life-threatening disorder known as trisomy 18. News

  • Alzheimer's disease patients harbor some cells with three copies of chromosome 21, known as trisomy 21, instead of the usual two.


  • Down syndrome, also called trisomy 21, is a genetic disorder first reported in 1866 by J. Langdon Down, a British physician.

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  • Antoneta Granic and team in their study "Alzheimer Ab Peptide Induces Chromosome Mis-segregation and Aneuploidy, including Trisomy 21; Requirement for Tau and APP," published in Molecular Biology of the Cell, provided the mechanism behind previous work by Potter's laboratory showing that all Alzheimer's disease patients harbour some cells with three copies of chromosome 21, known as trisomy 21, a characteristic shared by all the cells in people with the birth defect Down syndrome.

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  • Now known as trisomy-21 because of the third copy of the 21st chromosome, Down syndrome was first described by the English doctor, John Langdon Down, in 1866 but until Professor Lejeune's publication in 1959, the ultimate cause of Down Syndrome was unknown.


  • McDade learned during a routine sonogram that the baby she was carrying had a rare genetic disorder called trisomy 18 that frequently results in death either before or immediately after the child is born.

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