Editing Germline mutation (section)

=== Trisomy 21 ===
Trisomy 21 (also known as [[Down syndrome]]) results from a child having three copies of chromosome 21.<ref name=":3" /> This chromosome duplication occurs during germ cell formation, when both copies of chromosome 21 end up in the same [[Cell division|daughter cell]] in either the mother or father, and this mutant germ cell participates in fertilization of the zygote.<ref name=":3">{{cite journal | vauthors = Chandley AC | title = On the parental origin of de novo mutation in man | journal = Journal of Medical Genetics | volume = 28 | issue = 4 | pages = 217–23 | date = April 1991 | pmid = 1677423 | doi = 10.1136/jmg.28.4.217 | pmc=1016821}}</ref> Another, more common way this can occur is during the first cell division event after the formation of the zygote.<ref name=":3" /> The risk of Trisomy 21 increases with maternal age with the risk being 1/2000 (0.05%) at age 20 increasing to 1/100 (1%) at age 40.<ref>{{cite journal |last1=Hook |first1=EB |title=Rates of chromosome abnormalities at different maternal ages |journal=Obstetrics and Gynecology | date = September 1981 |volume=27 |issue=1 |pages=282–5 |doi=10.1016/0091-2182(82)90145-8 |pmid=6455611 }}</ref> This disease can be detected by non-invasive as well as invasive procedures prenatally. Non-invasive procedures include scanning for [[fetal DNA]] through maternal plasma via a blood sample.<ref>{{cite journal |last1=Ghanta |first1=Sujana |title=Non-Invasive Prenatal Detection of Trisomy 21 Using Tandem Single Nucleotide Polymorphisms |journal=PLOS ONE | date = October 2010 |volume=5 |issue=10 |pages=e13184 |doi=10.1371/journal.pone.0013184 |pmid=20949031 |pmc=2951898 |bibcode=2010PLoSO...513184G |doi-access=free }}</ref>