Predictors of dementia and mortality in Down’s syndrome

Down’s syndrome (DS) is a common genetic disorder affecting around 1 in 800 live births in the human population. The syndrome was first described by Down in 1866, in which he marked a collection of symptoms observed in 10% of the children with intellectual disability1. In 1959 Lejeune, Gautier and Turpin discovered the relation between DS and the triplication of chromosome 212. The diagnosis of DS is made by chromosome analysis, which can be initiated prenatally or postnatally based on the characteristic appearance of the newborn child. Down syndrome is in 95% of the cases caused by the presence of an entire extra copy of chromosome 21. A small number, 4% of the cases, have a partial trisomy, resulting from a translocation, and the attachment of an extra long arm of chromosome 21 to chromosome 14, 21 or 22. These infrequent cases have allowed the definition of the Down Syndrome Critical Region (DSCR) of chromosome 21 within the q22 region (about 5.4Mb in length)3 that includes a subset of genes that, when present in three copies, results in the major phenotypic features of DS, including the characteristic facial appearance, congenital heart disease, and intellectual disability4. Less than 1% of the cases are caused by mosaicisme, where some, but not all cells are trisomic.

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