Editing Down syndrome (section)

==Epidemiology==
[[File:Down risk by maternal age from jk morris.png|thumb|upright=1.5|The risk of having a Down syndrome pregnancy in relation to a [[Advanced maternal age|mother's age]]<ref name=Mor2002>{{cite journal | vauthors = Morris JK, Mutton DE, Alberman E | title = Revised estimates of the maternal age specific live birth prevalence of Down's syndrome | journal = Journal of Medical Screening | volume = 9 | issue = 1 | pages = 2–6 | year = 2002 | pmid = 11943789 | doi = 10.1136/jms.9.1.2 | doi-access = free }}</ref>]]
Down syndrome is the most common chromosomal abnormality in humans.<ref name="Malt2013" /> Globally, {{as of|2010|lc=y}}, Down syndrome occurs in about 1 per 1,000 births<ref name=Wei2010/> and results in about 17,000 deaths.<ref name=Loz2012>{{cite journal | vauthors = Lozano R, Naghavi M, Foreman K, Lim S, Shibuya K, Aboyans V, Abraham J, Adair T, Aggarwal R, Ahn SY, Alvarado M, Anderson HR, Anderson LM, Andrews KG, Atkinson C, Baddour LM, Barker-Collo S, Bartels DH, Bell ML, Benjamin EJ, Bennett D, Bhalla K, Bikbov B, Bin Abdulhak A, Birbeck G, Blyth F, Bolliger I, Boufous S, Bucello C, Burch M, Burney P, Carapetis J, Chen H, Chou D, Chugh SS, Coffeng LE, Colan SD, Colquhoun S, Colson KE, Condon J, Connor MD, Cooper LT, Corriere M, Cortinovis M, de Vaccaro KC, Couser W, Cowie BC, Criqui MH, Cross M, Dabhadkar KC, Dahodwala N, De Leo D, Degenhardt L, Delossantos A, Denenberg J, Des Jarlais DC, Dharmaratne SD, Dorsey ER, Driscoll T, Duber H, Ebel B, Erwin PJ, Espindola P, Ezzati M, Feigin V, Flaxman AD, Forouzanfar MH, Fowkes FG, Franklin R, Fransen M, Freeman MK, Gabriel SE, Gakidou E, Gaspari F, Gillum RF, Gonzalez-Medina D, Halasa YA, Haring D, Harrison JE, Havmoeller R, Hay RJ, Hoen B, Hotez PJ, Hoy D, Jacobsen KH, James SL, Jasrasaria R, Jayaraman S, Johns N, Karthikeyan G, Kassebaum N, Keren A, Khoo JP, Knowlton LM, Kobusingye O, Koranteng A, Krishnamurthi R, Lipnick M, Lipshultz SE, Ohno SL, Mabweijano J, MacIntyre MF, Mallinger L, March L, Marks GB, Marks R, Matsumori A, Matzopoulos R, Mayosi BM, McAnulty JH, McDermott MM, McGrath J, Mensah GA, Merriman TR, Michaud C, Miller M, Miller TR, Mock C, Mocumbi AO, Mokdad AA, Moran A, Mulholland K, Nair MN, Naldi L, Narayan KM, Nasseri K, Norman P, O'Donnell M, Omer SB, Ortblad K, Osborne R, Ozgediz D, Pahari B, Pandian JD, Rivero AP, Padilla RP, Perez-Ruiz F, Perico N, Phillips D, Pierce K, Pope CA, Porrini E, Pourmalek F, Raju M, Ranganathan D, Rehm JT, Rein DB, Remuzzi G, Rivara FP, Roberts T, De León FR, Rosenfeld LC, Rushton L, Sacco RL, Salomon JA, Sampson U, Sanman E, Schwebel DC, Segui-Gomez M, Shepard DS, Singh D, Singleton J, Sliwa K, Smith E, Steer A, Taylor JA, Thomas B, Tleyjeh IM, Towbin JA, Truelsen T, Undurraga EA, Venketasubramanian N, Vijayakumar L, Vos T, Wagner GR, Wang M, Wang W, Watt K, Weinstock MA, Weintraub R, Wilkinson JD, Woolf AD, Wulf S, Yeh PH, Yip P, Zabetian A, Zheng ZJ, Lopez AD, Murray CJ, AlMazroa MA, Memish ZA | display-authors = 6 | title = Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010 | journal = Lancet | volume = 380 | issue = 9859 | pages = 2095–2128 | date = December 2012 | pmid = 23245604 | pmc = 10790329 | doi = 10.1016/S0140-6736(12)61728-0 | hdl-access = free | s2cid = 1541253 | hdl = 10536/DRO/DU:30050819 }}</ref> More children are born with Down syndrome in countries where abortion is not allowed and in countries where pregnancy more commonly occurs at a later age.<ref name=Wei2010/> About 1.4 per 1,000 live births in the United States<ref name=Parker2010>{{cite journal | vauthors = Parker SE, Mai CT, Canfield MA, Rickard R, Wang Y, Meyer RE, Anderson P, Mason CA, Collins JS, Kirby RS, Correa A | display-authors = 6 | title = Updated National Birth Prevalence estimates for selected birth defects in the United States, 2004-2006 | journal = Birth Defects Research. Part A, Clinical and Molecular Teratology | volume = 88 | issue = 12 | pages = 1008–1016 | date = December 2010 | pmid = 20878909 | doi = 10.1002/bdra.20735 }}</ref> and 1.1 per 1,000 live births in Norway are affected.<ref name=Malt2013/> In the 1950s, in the United States, it occurred in 2 per 1,000 live births with the decrease since then due to prenatal screening and abortions.<ref name=Menk2006>{{cite book| vauthors = Menkes JH, Sarnat HB |title=Child neurology|year=2005|publisher=Lippincott Williams & Wilkins|location=Philadelphia, PA|isbn=978-0-7817-5104-9|page=228|url=https://books.google.com/books?id=gnjMX_jtvYoC&pg=PA228|edition=7th|url-status=live|archive-url=https://web.archive.org/web/20170123082801/https://books.google.com/books?id=gnjMX_jtvYoC&pg=PA228|archive-date=2017-01-23}}</ref> The number of pregnancies with Down syndrome is more than two times greater with many spontaneously aborting.<ref name=Nelson2011/> It is the cause of 8% of all [[congenital disorders]].<ref name=Wei2010/>

[[Maternal age effect|Maternal age]] affects the chances of having a pregnancy with Down syndrome.<ref name=Mor2002/> At age 20, the chance is 1 in 1,441; at age 30, it is 1 in 959; at age 40, it is 1 in 84; and at age 50 it is 1 in 44.<ref name=Mor2002/> Although the probability increases with maternal age, 70% of children with Down syndrome are born to women 35 years of age and younger, because younger people have more children.<ref name=Mor2002/> The [[Paternal age effect|father's older age]] is also a risk factor in women older than 35, but not in women younger than 35, and may partly explain the increase in risk as women age.<ref name=Doug2013>{{cite book | vauthors = Fisch H | chapter = The male biological clock |title=Paternal influences on human reproductive success|year=2013|publisher=Cambridge University Press|isbn=978-1-107-02448-9|page=65| chapter-url = https://books.google.com/books?id=O4Px3Q7f34QC&pg=PA65| veditors = Carrell DT |url-status=live|archive-url=https://web.archive.org/web/20170123082733/https://books.google.com/books?id=O4Px3Q7f34QC&pg=PA65|archive-date=2017-01-23}}</ref>