Down syndrome (DS), or trisomy 21, is a common disorder associated with several complex clinical phenotypes. Although several hypotheses have been put forward, it is unclear as to whether particular gene loci on chromosome 21 (HSA21) are sufficient to cause DS and its associated features. Here we present a high-resolution genetic map of DS phenotypes based on an analysis of 30 subjects carrying rare segmental trisomies of various regions of HSA21. By using state-ofthe-art genomics technologies we mapped segmental trisomies at exon-level resolution and identified discrete regions of 1.8 -16.3 Mb likely to be involved in the development of 8 DS phenotypes, 4 of which are congenital malformations, including acute megakaryocytic leukemia, transient myeloproliferative disorder, Hirschsprung disease, duodenal stenosis, imperforate anus, severe mental retardation, DS-Alzheimer Disease, and DS-specific congenital heart disease (DSCHD). Our DS-phenotypic maps located DSCHD to a <2-Mb interval. Furthermore, the map enabled us to present evidence against the necessary involvement of other loci as well as specific hypotheses that have been put forward in relation to the etiology of DS-i.e., the presence of a single DS consensus region and the sufficiency of DSCR1 and DYRK1A, or APP, in causing several severe DS phenotypes. Our study demonstrates the value of combining advanced genomics with cohorts of rare patients for studying DS, a prototype for the role of copy-number variation in complex disease. copy number variants ͉ genomic structural variation ͉ human genome ͉ congenital heart disease ͉ leukemia F or over two decades trisomy 21 has represented a prototype disorder for the study of human aneuploidy and copy-number variation (1, 2), but the genes responsible for most Down syndrome (DS) phenotypes are still unknown. The analysis of several overlapping segmental trisomies 21 has led to the suggestion that dosage alteration through duplication of an extended region on chromosome 21 (HSA21) is associated with DS features (2-5, 42). However, humans with segmental trisomy 21 are rare, and thus humanbased DS-phenotypic maps have been of low resolution, far beyond the level of few or single genes, or even exons. Consequently, gene-disease links have often been based on indirect evidence from cellular or animal models (6, 7). Moreover, current hypotheses argue for the existence of a critical region, the DS consensus region (DSCR), responsible for most severe DS features (6, 8, 9), or presume the causative role of a small set of genes including DSCR1 and DYRK1A, or APP, for these phenotypes (6, 7).By using state-of-the-art genomics together with a large panel of partially trisomic individuals, we present the highest resolution DS phenotype map to date and identify distinct genomic regions that likely contribute to the manifestation of 8 DS features. Four of these phenotypes have never been associated with a particular region of HSA21. The map also enables us to rule out the necessary contribution of other HSA21 regions, thus pr...

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Down syndrome (DS) is characterized by increased mortality rates, both during early and later stages of life, and age-specific mortality risk remains higher in adults with DS compared with the overall population of people with mental retardation and with typically developing populations. Causes of increased mortality rates early in life are primarily due to the increased incidence of congenital heart disease and leukemia, while causes of higher mortality rates later in life may be due to a number of factors, two of which are an increased risk for Alzheimer's disease (AD) and an apparent tendency toward premature aging. In this article, we describe the increase in lifespan for people with DS that has occurred over the past 100 years, as well as advances in the understanding of the occurrence of AD in adults with DS. Aspects of the neurobiology of AD, including the role of amyloid, oxidative stress, Cu/ZN dismutase (SOD-1), as well as advances in neuroimaging are presented. The function of risk factors in the observed heterogeneity in the expression of AD dementia in adults with DS, as well as the need for sensitive and specific biomarkers of the clinical and pathological progressing of AD in adults with DS is considered.

In the United States, estimates indicate there are between 250,000 and 400,000 individuals with Down syndrome (DS), and nearly all will develop Alzheimer's disease (AD) pathology starting in their 30s. With the current lifespan being 55 to 60 years, approximately 70% will develop dementia, and if their life expectancy continues to increase, the number of individuals developing AD will concomitantly increase. Pathogenic and mechanistic links between DS and Alzheimer's prompted the Alzheimer's Association to partner with the Linda Crnic Institute for Down Syndrome and the Global Down Syndrome Foundation at a workshop of AD and DS experts to discuss similarities and differences, challenges, and future directions for this field. The workshop articulated a set of research priorities: (1) target identification and drug development, (2) clinical and pathological staging, (3) cognitive assessment and clinical trials, and (4) partnerships and collaborations with the ultimate goal to deliver effective disease-modifying treatments.