Editing Trisomy (section)

==Human trisomy==
[[File:Trisomie 21 Genom-Schema.gif|thumb|[[Karyotype]] of a human with Trisomy 21 (Down syndrome)]]
Trisomies can occur with any [[chromosome]], but often result in [[spontaneous abortion]] (miscarriage) rather than live birth. For example, [[Trisomy 16]] is most common in human pregnancies, occurring in more than 1%, but the only surviving embryos are those having some normal cells in addition to the trisomic cells ([[Mosaic (genetics)|mosaic]] trisomy 16).<ref name="T Hassold et al">{{cite journal |pmc=1801507 |title=Recombination and maternal age-dependent nondisjunction: molecular studies of trisomy 16 |year=1995 |volume=57 |issue=4 |pmid=7573048 |last1=Hassold |first1=T |last2=Merrill |first2=M |last3=Adkins |first3=K |last4=Freeman |first4=S |last5=Sherman |first5=S |pages=867–74 |journal=American Journal of Human Genetics}}</ref> Furthermore, even these embryos usually suffer [[miscarriage]] in the first trimester.

The most common types of human [[autosome|autosomal]] (non-sex chromosome) trisomy that survive to birth are:

*Trisomy 21 ([[Down syndrome]])
*Trisomy 18 ([[Edwards syndrome]])
*Trisomy 13 ([[Patau syndrome]])
*[[Trisomy 9]]
*[[Trisomy 8]] (Warkany syndrome 2)

Of these, Trisomy 21 and Trisomy 18 are the most common. In rare cases, a fetus with Trisomy 13 can survive, giving rise to [[Patau syndrome]]. Autosomal trisomy can be associated with birth defects, [[intellectual disability]] and shortened life.

''Trisomy of [[sex chromosomes]]'' can also occur and include:<ref name="O'Connor">{{cite journal | url=http://www.nature.com/scitable/topicpage/chromosomal-abnormalities-aneuploidies-290 | title=Chromosomal Abnormalities: Aneuploidies | author=O'Connor, Clare | journal=Nature Education | year=2008 | volume=1 | issue=1 | pages=172}}</ref>

*XXX ([[Triple X syndrome]])
*XXY ([[Klinefelter syndrome]])
*[[XYY syndrome|XYY]] (Jacobs syndrome)
Compared to trisomy of the autosomal chromosomes, trisomy of the sex chromosomes normally has less severe consequences. Individuals may show few or no symptoms and have a normal life expectancy.<ref name="O'Connor"/>