Down's syndrome

Down's syndrome (DS) is the most common genetic cause of intellectual disability, occurring in 1 in 800 births worldwide.[1]Bull MJ. Down syndrome. N Engl J Med. 2020 Jun 11;382(24):2344-52. http://www.ncbi.nlm.nih.gov/pubmed/32521135?tool=bestpractice.com In the US, DS has an incidence of 1 in 792 live births, or about 5300 of the 4 million infants born yearly.[3]de Graaf G, Buckley F, Skotko BG. Estimates of the live births, natural losses, and elective terminations with Down syndrome in the United States. Am J Med Genet A. 2015 Apr;167A(4):756-67. https://www.doi.org/10.1002/ajmg.a.37001 http://www.ncbi.nlm.nih.gov/pubmed/25822844?tool=bestpractice.com Population estimates suggest that, as of 2010, the prevalence of DS in the US was approximately 6.7 per 10,000 individuals.[4]de Graaf G, Buckley F, Skotko BG. Estimation of the number of people with Down syndrome in the United States. Genet Med. 2017 Apr;19(4):439-47. https://www.gimjournal.org/article/S1098-3600(21)02433-3/fulltext http://www.ncbi.nlm.nih.gov/pubmed/27608174?tool=bestpractice.com

DS occurs in all ethnic groups, socioeconomic levels, and geographical regions. Standard trisomy 21, the presence of an extra chromosome 21, is caused by chromosome non-disjunction and occurs in 95% of cases. In about 4% to 5% of individuals with DS, the trisomy results from a chromosome translocation, and the remaining 1% of cases of DS are mosaic with a combination of typical and trisomic cells.[5]Hunter AGW. Down syndrome. In: Cassidy SB, Allanson JE, eds. Management of genetic syndromes, 2nd ed. Hoboken, NJ: Wiley-Liss; 2005:191-210.